research paper on animal nutrition

Recent Advances in Animal Nutrition and Metabolism

• © 2022
• Guoyao Wu 0

Department of Animal Science, Texas A&M University, College Station, USA

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• Covers hot topics in the nutrition and metabolism of terrestrial and aquatic animals
• Addresses the use of new genome-editing biotechnologies to generate animals as bioreactors
• Highlights the use of animals as models in biomedical research to prevent and treat human diseases

Part of the book series: Advances in Experimental Medicine and Biology (AEMB, volume 1354)

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Table of contents (17 chapters)

Front matter, nutrition and metabolism: foundations for animal growth, development, reproduction, and health, insights into the regulation of implantation and placentation in humans, rodents, sheep, and pigs.

• Claire Stenhouse, Heewon Seo, Guoyao Wu, Gregory A. Johnson, Fuller W. Bazer

A Role for Fructose Metabolism in Development of Sheep and Pig Conceptuses

• Robyn M. Moses, Avery C. Kramer, Heewon Seo, Guoyao Wu, Gregory A. Johnson, Fuller W. Bazer

Nutritional Regulation of Embryonic Survival, Growth, and Development

• Lawrence P. Reynolds, Kyle J. McLean, Kacie L. McCarthy, Wellison J. S. Diniz, Ana Clara B. Menezes, J. Chris Forcherio et al.

Phosphate, Calcium, and Vitamin D: Key Regulators of Fetal and Placental Development in Mammals

• Claire Stenhouse, Larry J. Suva, Dana Gaddy, Guoyao Wu, Fuller W. Bazer

Nutritional and Physiological Regulation of Water Transport in the Conceptus

• Cui Zhu, Zongyong Jiang, Gregory A. Johnson, Robert C. Burghardt, Fuller W. Bazer, Guoyao Wu

Amino Acids in Microbial Metabolism and Function

• Zhaolai Dai, Zhenlong Wu, Weiyun Zhu, Guoyao Wu

Potential Replacements for Antibiotic Growth Promoters in Poultry: Interactions at the Gut Level and Their Impact on Host Immunity

• Christina L. Swaggerty, Cristiano Bortoluzzi, Annah Lee, Cinthia Eyng, Gabriela Dal Pont, Michael H. Kogut

Microbiomes in the Intestine of Developing Pigs: Implications for Nutrition and Health

• Chunlong Mu, Yu Pi, Chuanjian Zhang, Weiyun Zhu

L-Arginine Nutrition and Metabolism in Ruminants

• Guoyao Wu, Fuller W. Bazer, M. Carey Satterfield, Kyler R. Gilbreath, Erin A. Posey, Yuxiang Sun

Hepatic Glucose Metabolism and Its Disorders in Fish

• Xinyu Li, Tao Han, Shixuan Zheng, Guoyao Wu

Protein-Sourced Feedstuffs for Aquatic Animals in Nutrition Research and Aquaculture

• Sichao Jia, Xinyu Li, Wenliang He, Guoyao Wu

Functional Molecules of Intestinal Mucosal Products and Peptones in Animal Nutrition and Health

• Peng Li, Guoyao Wu

Use of Genome Editing Techniques to Produce Transgenic Farm Animals

• Alayna N. Hay, Kayla Farrell, Caroline M. Leeth, Kiho Lee

Cows as Bioreactors for the Production of Nutritionally and Biomedically Significant Proteins

• P. S. Monzani, P. R. Adona, S. A. Long, M. B. Wheeler

Use of Agriculturally Important Animals as Models in Biomedical Research

• Brandon I. Smith, Kristen E. Govoni

Pigs ( Sus Scrofa ) in Biomedical Research

• Werner G. Bergen

Back Matter

• Animal Production

About this book

This book covers hot topics in the nutrition and metabolism of terrestrial and aquatic animals, including the interorgan transport and utilization of water, minerals, amino acids, glucose, and fructose; the development of alternatives to in-feed antibiotics for animals (e.g., swine and poultry); and metabolic disorders (or diseases) resulting from nutrient deficiencies. It enables readers to understand the crucial roles of nutrients in the nutrition, growth, development, and health of animals. Such knowledge has important implications for humans.  

Readers will also learn from well-written chapters about the use of new genome-editing biotechnologies to generate animals (e.g., cows and swine) as bioreactors that can produce large amounts of pharmaceutical proteins and other molecules to improve the health and well-being of humans and other animals, as well as the growth and productivity of farm animals. Furthermore, the book provides usefulinformation on the use of animals (e.g., cattle, swine, sheep, chickens, and fish) as models in biomedical research to prevent and treat human diseases, develop infant formulas, and improve the cardiovascular and metabolic health of offspring with prenatal growth restriction. 

Editor of this book is an internationally recognized expert in nutrition and metabolisms. He has about 40 years of experience with research and teaching at world-class universities in the subject matters. He has published more than 660 papers in peer-reviewed journals, 90 chapters in books, and authored two text/reference books, with a very high H-index of 127 and more than 66,000 citations in Google Scholar. 

This publication is a useful reference for nutrition and biomedical professionals, as well as undergraduate and graduate students in animal science, aquaculture, zoology, wildlife, veterinary medicine, biology, biochemistry, food science, nutrition, pharmacology, physiology, toxicology, and other related disciplines. In addition, all chapters provide general and specific references to nutrition and metabolism for researchers and practitioners in animal agriculture (including aquaculture), dietitians, animal and human medicines, and for government policy makers.

Editors and Affiliations

Department of animal science, texas a&m university, college station, usa, about the editor.

Guoyao Wu is Distinguished Professor, University Faculty Fellow, and AgriLife Research Senior Faculty Fellow in the Department of Animal Science. He also holds appointments with the Graduate Faculty of Nutrition, the Departments of Systems Biology and Translational Medicine and Veterinary Integrative Biosciences. 

Dr. Wu teaches graduate courses in protein metabolism and nutritional biochemistry. He conducts research in protein and amino acid metabolism at molecular, cellular, andwhole body levels . The animal models used in his research include cattle, chicks, pigs, rats, mice, fish, shrimp, and sheep. 

Professional memberships include the American Society of Animal Science, the American Society for Nutritional Sciences, Society for Study of Reproduction, American Association for the Advancement of Sciences, and American Heart Association. Dr. Wu currently serves on the Editorial Board of the Journal of Nutritional Biochemistry. He is Editor of “Amino Acids” and “Frontiers in Bioscience.”

Bibliographic Information

Book Title : Recent Advances in Animal Nutrition and Metabolism

Editors : Guoyao Wu

Series Title : Advances in Experimental Medicine and Biology

DOI : https://doi.org/10.1007/978-3-030-85686-1

Publisher : Springer Cham

eBook Packages : Biomedical and Life Sciences , Biomedical and Life Sciences (R0)

Copyright Information : The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022

Hardcover ISBN : 978-3-030-85685-4 Published: 23 November 2021

Softcover ISBN : 978-3-030-85688-5 Published: 24 November 2022

eBook ISBN : 978-3-030-85686-1 Published: 22 November 2021

Series ISSN : 0065-2598

Series E-ISSN : 2214-8019

Edition Number : 1

Number of Pages : VI, 346

Number of Illustrations : 16 b/w illustrations, 27 illustrations in colour

Topics : Biomedical Engineering/Biotechnology , Biochemistry, general , Animal Physiology , Agriculture

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Article Contents

Introduction, regulatory definitions of natural, natural beyond the regulatory definitions, impact on pet health, the future of natural pet nutrition, literature cited.

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Natural pet food: A review of natural diets and their impact on canine and feline physiology

• Article contents
• Figures & tables
• Supplementary Data

P. R. Buff, R. A. Carter, J. E. Bauer, J. H. Kersey, Natural pet food: A review of natural diets and their impact on canine and feline physiology, Journal of Animal Science , Volume 92, Issue 9, September 2014, Pages 3781–3791, https://doi.org/10.2527/jas.2014-7789

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The purpose of this review is to clarify the definition of “natural” as it pertains to commercial pet food and to summarize the scientific findings related to natural ingredients in pet foods and natural diets on the impact of pet health and physiology. The term “natural,” when used to market commercial pet foods or pet food ingredients in the United States, has been defined by the Association of American Feed Control Officials and requires, at minimum, that the pet food be preserved with natural preservatives. However, pet owners may consider natural as something different than the regulatory definition. The natural pet food trend has focused on the inclusion of whole ingredients, including meats, fruits, and vegetables; avoiding ingredients perceived as heavily processed, including refined grains, fiber sources, and byproducts; and feeding according to ancestral or instinctual nutritional philosophies. Current scientific evidence supporting nutritional benefits of natural pet food products is limited to evaluations of dietary macronutrient profiles, fractionation of ingredients, and the processing of ingredients and final product. Domestic cats select a macronutrient profile (52% of ME from protein) similar to the diet of wild cats. Dogs have evolved much differently in their ability to metabolize carbohydrates and select a diet lower in protein (30% of ME from protein) than the diet of wild wolves. The inclusion of whole food ingredients in natural pet foods as opposed to fractionated ingredients may result in higher nutrient concentrations, including phytonutrients. Additionally, the processing of commercial pet food can impact digestibility, nutrient bioavailability, and safety, which are particularly important considerations with new product formats in the natural pet food category. Future opportunities exist to better understand the effect of natural diets on health and nutrition outcomes and to better integrate sustainable practices in the production of natural pet foods.

Throughout history, humans have associated with dogs and cats in various ways, including protection, rodent control, hunting, and companionship. Diets of dogs and cats have shifted, as a result of domestication, from hunting and scavenging to diets formulated for their specific nutritional requirements. Changes in human diets through the development of agricultural practices have fostered this shift. In the United States, 63% of pet owners consider their pets to be family members ( AVMA, 2012b ). Anthropomorphism of dogs and cats has resulted in pet owner preference for pet foods containing ingredients that they find in their own diet and processed in a way to maintain the nutritional integrity of the ingredients and ensure food safety. Contemporary trends in human diets in developed regions of the world are including more fresh fruits and vegetables ( Barnard, 2010 ) and whole grains ( Griffiths, 2010 ). This paradigm has resulted in the emergence of the natural pet food segment. The natural pet food segment in the United States has grown steadily, from US$2.0 billion in 2008 to $3.9 billion in 2012 ( Lummis, 2012 ).

The expansion of the natural pet food segment has led to a wide spectrum of products with different nutritional strategies applied across brands and introducing unique philosophies on what defines a natural pet food product ( Lummis, 2012 ). This variability has led to confusion and disagreement as to the true definition of natural pet foods and natural pet nutrition. Additionally, the application of human food trends often is used to support functional health benefits of natural pet food products despite limited scientific evidence supporting the benefits in companion animals. Therefore, the purpose of this review is to clarify the definition of natural as it pertains to commercially manufactured pet foods and summarize the scientific findings regarding natural ingredients used regarding their impact on pet health and physiology. It should be noted, however, that although home-prepared diets may meet certain definitions of natural, they will not be discussed here because these are not officially recognized by any regulatory agency.

Pet food manufacturers must meet the regulatory definition of natural to market a pet food as natural. The definition of natural applies to both pet food ingredients and pet food products. However, regulatory agencies internationally disagree on the definition of natural. Consider, for example, differences that exist between the United States and European definitions of natural as it applies to pet food ingredients or products. In the United States, the regulatory definition of natural has been developed by the Association of American Feed Control Officials ( AAFCO ), a voluntary membership association of state feed officials charged with developing model regulations to be adopted by states to regulate animal feeds and animal drug remedies. The AAFCO definition of natural states the following:

…A feed or ingredient derived solely from plant, animal or mined sources, either in its unprocessed state or having been subject to physical processing, heat processing, rendering, purification, extraction, hydrolysis, enzymolysis or fermentation, but not having been produced by or subject to a chemically synthetic process and not containing any additives or processing aids that are chemically synthetic except in amounts as might occur unavoidably in good manufacturing practices. ( AAFCO, 2013 )

Synthetic trace nutrients are allowed by the AAFCO in natural pet foods as long as they have nutritive value. In this case, a disclaimer on the package is used to inform the consumer that the vitamins, minerals, or other trace nutrients are not natural ( AAFCO, 2013 ). This enables the formulation of complete and balanced natural pet food products. A complete and balanced diet should have all essential nutrients in the proper amount and proportions based on authoritative recommendations, such as the NRC ( NRC, 2006 ). Guidelines for nutrient profiles for both dogs and cats by which a food may be considered complete and balanced are provided by the AAFCO (2013) . The complete and balanced statement on the label indicates the formula provides all the essential nutrients necessary to maintain life (except water) when fed as the sole source of energy in the diet.

The European Union use of the term natural is defined by The European Pet Food Industry Federation ( FEDIAF ) and states

The term “natural” should be used only to describe pet food components (derived from plant, animal, microorganism or minerals) to which nothing has been added and which have been subjected only to such physical processing as to make them suitable for pet food production and maintaining the natural composition. ( FEDIAF, 2011 )

Processing of components including freezing, concentration, extraction (without chemicals), drying, pasteurization, or smoking (without chemicals) is acceptable as far as is maintains the natural composition. Microbiological and enzymatic processes, hydrolysis, or natural fermentation processes (without the use of genetically modified organisms) are acceptable with the use of the term natural ( FEDIAF, 2011 ). Similar to the AAFCO definition, the FEDIAF definition allows the use of synthetic vitamins and minerals with an appropriate disclaimer. Additionally, guidelines for nutrient profiles for both dogs and cats by which a food may be considered complete and balanced are provided by the FEDIAF (2011) .

Given the above definitions, it is noteworthy that there are distinct differences between the AAFCO and FEDIAF approaches to defining natural. While both allow many of the same processes, the FEDIAF definition excludes the use of chemical processing aids and requires that processing does not change the natural composition of the ingredient. For example, under the AAFCO definition, hexane-extracted soybean oil is considered a natural pet food ingredient since the hexane is not present in the final ingredient except in amounts as might occur unavoidably in good manufacturing practices. However, according to the FEDIAF definition, hexane-extracted oil would not be considered natural since it uses chemical extraction. Conversely, cold pressed oil would be considered natural according to the FEDIAF definition because it does not use chemical extraction. An example of an instance where the natural composition of an ingredient is not maintained is carrot pulp from which carotene has been extracted. According to the FEDIAF definition, this would not be considered a natural ingredient because the natural composition has changed; however, this may be considered a natural ingredient according to the AAFCO definition. Another difference in regulatory definitions is that the use of genetically modified ingredients in natural products is currently not addressed in the AAFCO definition of natural but is excluded by the FEDIAF definition. The difference between these definitions is instrumental to defining natural ingredients in today's global marketplace and underscores both the functional and regulatory characterizations of natural pet foods for dogs and cats. As such, it presents an ongoing challenge for natural pet food product formulation because it necessitates a different approach to product formulation in different regions of the world.

Inconsistencies in the definition of natural among international regulatory agencies and the lack of visibility and understanding of regulatory definitions by pet owners have contributed to misperceptions about natural pet food products. Therefore, many natural pet food consumers seek out products or ingredients with claims of human-grade, organic, holistic, ancestral, or instinctual and avoid ingredients perceived as fillers or byproducts ( Shmalberg, 2013 ); however, these terms are not addressed in the current regulatory definitions of natural.

Each step of the manufacturing process of pet food can positively or negatively affect the naturalness of the final product, including crop and livestock production activities, ingredient processing and preservation, and kibble extrusion or canning of final product ( Fig. 1 ). Consequently, various steps of the manufacturing process are considered by pet owners, manufacturers, nutritionists, or regulatory agencies when determining if an ingredient or product is natural. For example, the AAFCO definition of natural primarily considers ingredient processing, whereas consumers may impose additional selection criteria based on opinions and beliefs, such as exclusion of ingredients perceived as having low nutritional value. On the other hand, consumers, nutritionists, or manufacturers that determine a natural diet based on pet physiology or pet preference may consider nutrient composition, food format, or ingredient origin (e.g., plant vs. animal).

Pet food manufacturing process steps considered by different entities for defining “natural.” Labels within a circle represent the regulatory consideration of the Association of American Feed Control Officials definition of natural, consumer perspectives of natural, and natural pet nutrition concepts based on pet physiology and preferences.

Differences in natural ingredient processing highlight the difficulties in classifying ingredients or pet food products as natural. Therefore, identifying natural ingredients is a complex process in which it is critical to have a thorough understanding of ingredients through their production, preparation, processing, and preservation. Even within ingredient processing techniques, there is a continuum of what may be considered more or less natural ( Fig. 2 ). For example, an identical raw material can be processed either as a whole ingredient, fractionated to isolate specific parts of the ingredient, or stabilized by adding synthetic preservatives. According to the AAFCO definition of natural, the whole cooked ingredient and fractionated ingredients would be considered natural but the synthetically preserved ingredient would not. However, from a consumer standpoint the defining of the ingredient as natural may not be as clear-cut. Many consumers would consider the whole cooked ingredient as natural but not the fractionated or synthetically preserved ingredient.

The continuum of natural ingredients. The Association of American Feed Control Officials (AAFCO) and The European Pet Food Industry Federation (FEDIAF) regulatory definitions of natural are highlighted along the continuum. Examples of pet food ingredients are given for each step of the continuum. GM = Genetically Modified.

Natural Diets

Natural diets, including instinctual or ancestral diets, are based on feeding pets according to their physiological capabilities or preferences, rather than simply meeting the regulatory definition of a natural pet food product. Instinctual diets are based on the philosophy of feeding pets according to their innate preferences, with the assumption that animals will self-select foods to meet their nutritional needs. Ancestral diets are based on the philosophy of feeding pets a diet similar to evolutionary ancestors, with the assumption that such a diet aligns with the physiological needs and metabolic capabilities of companion animals. Regardless of philosophical basis, both instinctual and ancestral diets typically contain higher protein and lower carbohydrate concentrations than the majority of dry pet foods on the market. There are no regulatory definitions of instinctual or ancestral diets; therefore, the nutrient composition of commercial pet food products may not accurately apply to instinctual or ancestral nutritional philosophies.

Instinctual Diets.

Recent research using nutritional geometry in a controlled environment has demonstrated that dogs of various breeds select a macronutrient profile in which 30% of their ME comes from protein, 63% from fat, and 7% from carbohydrates ( Hewson-Hughes et al., 2013 ). Similar research in cats indicates they select 52% of their ME from protein, 36% from fat, and 12% from carbohydrates ( Hewson-Hughes et al., 2011 ). Given their strict carnivorous nature, it is not surprising that cats show a preference for higher protein diets compared to omnivorous dogs. By contrast, dogs apparently find dietary fat particularly palatable, which is consistent with minimal adverse health effects of high fat diets in healthy populations of dogs ( Bauer, 2006 ). However, it is unknown whether the above distributions of macronutrients would provide optimal nutrition, given that the preferred macronutrient levels are substantially different than minimal requirements or recommended allowances outlined by the NRC ( NRC, 2006 ).

Ancestral Diets.

It is recognized that domesticated dogs evolved from wolves ( Canis lupus lupus ; Serpell, 1995 ). From archeological evidence, it is believed dogs were the first animal to be domesticated by humans around 14,000 yr ago ( Clutton-Brock, 1995 ). Domestication of cats is more recent than dogs, as remains of cats dating back 6,000 yr ago have been found in Cyprus ( Serpell, 2000 ). Consequently, some natural dog foods are marketed based on high meat and protein formulations believed suitable for wolves due to their evolutionary connection and genetic similarities. However, domesticated dogs are no longer wolves because domestication as Canis lupus familiaris has modified not only their social and cognitive attributes but also the types of foodstuffs that are suitable for them ( Hemmer, 1990 ). Recent evidence has been reported in which candidate mutations in key genes of dogs compared to wolves provide functional support for increased capability for starch digestion ( Axelsson et al., 2013 ) compared to the carnivorous wolf diet ( Stahler et al., 2006 ). This supports a previous report by Serpell (1995) that dogs descended from a subset of wolves that had been more socially adapted to human contact. These data help explain the omnivorous nature of domestic dogs versus carnivorous wolves.

In nature, it appears the primary component of the canine diet is animal protein, but as noted above, domestic canines can obtain nutritional requirements from plant sources as well. Feral dogs are known to hunt in packs, similar to wild canines, and eat a wide variety of foods. The diet of wolves consists primarily of animal protein and they typically hunt larger prey, such as elk, eating the nutrient-dense organs first followed by muscle tissue ( Stahler et al., 2006 ). Analysis of 50 diets consumed by wolves revealed average nutrient intake of 35.5 g protein, 13.2 g fat, and 0.8 g carbohydrate per MJ ME, which reflects a macronutrient profile of 52% ME from protein, 47% ME from fat, and 1% ME from carbohydrate ( Hendriks, 2013 ). Feral dogs typically hunt small prey and forage on berries and some plants ( Boitani and Ciucci, 1995 ). Jackals ( Canis aureus ) often raid stores of cultivated fruit and consume large quantities of grass ( Ewer, 1973 ). Wild canines and feral dogs must exert a considerable amount of energy to acquire food and therefore consume foods that are more easily available in the environment in which they live. This evidence supports the hypothesis that canine species are highly adaptable to various diets, and the diet they choose is dictated by the environment in which they live.

Through mitochondrial DNA analysis, it has been reported that the domestic cat ( Felis catus ) is most closely related to the European wildcat ( Felis silvestris ), the African wildcat ( Felis libyca ), and the sand cat ( Felis nigripes ; Johnson and O'Brien, 1997 ). These species of wild cats closely resemble the domestic cat in appearance, and African wildcats have been kept as pets ( Smithers, 1968 ). Many of the behavioral signs observed in domestic cats, such as purring, meowing, hissing, and spitting, have been observed in most wild species ( Serpell, 2000 ).

The natural diet of feral cats consists primarily of small mammals, birds, fish, reptiles, and invertebrates, with a macronutrient profile of 52% ME from protein, 46% ME from fat, and 2% ME from carbohydrate ( Plantinga et al., 2011 ). Studies on the preferred macronutrient profile of domestic cats indicate the instinctual dietary preference of domestic cats closely resembles the nutrient composition of cats in the wild ( Hewson-Hughes et al., 2011 ). Studies have been conducted comparing the digestibility of various raw meat based diets of captive exotic felids to domestic cats. Vester et al. (2010) reported apparent total tract digestibility in cheetahs ( Acinonyx jubatus ), jaguars ( Panthera onca ), Malayan tigers ( Panthera tigris corbetti ), Amur tigers ( Panthera tigris altaica ), and domestic short hair cats ( F. catus ) consuming 2 different raw meat based diets. These investigators found no differences in digestibility measure between the captive exotic felids. Differences between domestic cats and jaguars were observed for DM, CP, fat, and GE digestibilities ( P < 0.05). Differences were also observed between domestic cats and Amur tigers for DM, OM, CP, fat, and GE digestibility ( P < 0.05). Additionally, differences were observed between domestic cats and Malayan tigers for CP, fat, and GE digestibilities ( P < 0.05). No differences were observed between domestic cats and cheetahs. A later report from the same laboratory ( Kerr et al., 2013 ) compared total tract digestibility of domestic cats, African wildcats ( Felis silvestris tritrami ), jaguars, and Malayan tigers fed meat based raw diets. In this study, there were no observed differences between species for total tract DM, OM, and GE digestibilities. However, they did find differences between apparent total tract CP digestibility between domestic cats and Malayan tigers, but no differences in CP digestibility were observed between domestic cats and other species in this study. Unlike the evolution of dogs, cats appear to have retained much of the dietary preference, behavioral attributes, and physiological digestive function as the wild species. More research needs to be conducted to determine impact of ancestral diets on health of pets.

Pet Physiology and Metabolism.

The basis behind feeding natural diets, including instinctual and ancestral diets, is to meet nutritional needs and align with physiological and metabolic capabilities to promote health in companion animals. Therefore, to better evaluate the extent to which such diets are appropriate for companion animals, some appreciation of both dog and cat digestive physiology is important.

Both dogs and cats have the ability enzymatically (maltase, sucrose, and lactase) to digest carbohydrates ( Hore and Messer, 1968 ). Morris et al. (1977) showed cats are able to efficiently digest glucose, sucrose, lactose, dextrin, and starch (apparent digestibility 94–100%). Additionally, cats have been reported to have lower enzymatic activities for carbohydrate digestion compared to other species ( Kienzle, 1993a , b , c , d ) and physiologic responses differ by carbohydrate type and thermal processing ( Kienzle, 1994 ). These results indicate that although cats have the ability to efficiently digest carbohydrates, their capacity for carbohydrate digestion may be limited, as evidenced by digestive disorders, such as diarrhea, flatulence, and bloating, when high concentrations of carbohydrates (>5 g/kg BW) are fed ( Kienzle, 1993b ).

Relative to humans, dogs have an increased capacity for fat oxidation, generating twice the amount of energy from fat oxidation at rest and during exercise ( McClelland et al., 1994 ). However, dogs have responses similar to humans in carbohydrate metabolism following a meal, with carbohydrate amount and type dictating glycemic response ( Nguyen et al., 1998 ; Carciofi et al., 2008 ; Elliott et al., 2012 ). For example, when 12 working hounds were fed a high protein (49%), low carbohydrate (13%) diet they had a delayed peak glucose concentration and sustained glucose response compared to when fed a lower protein (22%), higher carbohydrate (45%) diet ( Hill et al., 2009 ).

The metabolism of cats is adapted for gluconeogenesis rather than glucose clearance, including no detectable hepatic glucokinase activity and higher activities of pyruvate carboxylase, fructose-1,6-biphosphatase, and glucose-6-phosphatase in feline compared to canine livers ( Washizu et al., 1999 ; Tanaka et al., 2005 ). However, there is currently limited evidence to suggest that moderate concentrations of carbohydrates in the diet are detrimental to the metabolism or health of cats ( Verbrugghe et al., 2012 ). For example, both high (47% energy from carbohydrate compared to 26–27%) or low (7% energy from carbohydrate compared to 25–29%) concentrations of dietary carbohydrate reduce insulin sensitivity in cats ( Farrow et al., 2002 ; Verbrugghe et al., 2010 ). Additionally, while protein intake of 48 versus 28% energy from protein does not affect insulin sensitivity ( Leray et al., 2006 ), high concentrations of dietary fat (51% energy from fat compared to 33%) reduces glucose tolerance in cats ( Thiess et al., 2004 ).

Although protein or essential AA intakes beyond the recommended allowance ( NRC, 2006 ) have not been reported to provide added benefit for pets requiring maintenance nutrient needs, there is evidence to suggest a benefit during physiological states other than adult maintenance, such as obesity and athletic training. High protein diets (>100 g crude protein/1,000 kcal ME) have been shown to effectively facilitate weight loss in obese dogs while maintaining lean body mass ( Diez et al., 2002 ; Blanchard et al., 2004 ; German et al., 2010 ). Hoenig et al. (2007) investigated effects of a high-carbohydrate/low-protein (28% protein/38% carbohydrate) and a high-protein/low-carbohydrate (45% protein/25% carbohydrate) diet during weight loss. Weight loss modified selected hormones and other metabolites independent of diet. These investigators also found that the high protein diet was beneficial in cats to maintain normal insulin sensitivity of fat metabolism during caloric restriction. It should be noted that studies showing beneficial effects of higher protein diets in overweight or obese companion animals also used caloric restriction and often lower fat concentrations than natural diets to achieve these benefits.

Diets high in protein (>30% ME from protein) or fat (>50% ME from fat) have been shown to have a beneficial effect on exercise performance in dogs. Fat adaptation to greater than 50% of ME from fat was found to improve aerobic performance ( Downey et al., 1980 ) and to spare glycogen utilization in dogs ( Reynolds et al., 1995 ). Beagles ran for 20 miles (140 min) when fed high fat (53–67% of energy) diets but became exhausted after only 15 miles (100 min) when fed a moderate fat (29% of energy) diet ( Downey et al., 1980 ). A high carbohydrate (60% ME from carbohydrate), low fat (15% ME from fat) diet fed to sled dogs resulted in higher ( P < 0.05) resting muscle glycogen concentrations compared with a high fat (60% ME from fat), low carbohydrate (15% ME from carbohydrate) diet, but the rate of glycogen utilization was greater ( P < 0.05) during an anaerobic exercise bout; therefore, the final muscle glycogen concentration was unchanged ( Reynolds et al., 1995 ). In racing sled dogs, protein concentration is also important, given there is progressive development of stress anemia below 32% ME from protein ( Kronfeld et al., 1994 ). Conversely, moderate protein and fat (24% ME from protein, 33% ME from fat, and 43% ME from carbohydrate) has been shown to be more beneficial for sprint performance in dogs, as indicated by faster racing times (32.43 ± 0.48 vs. 32.61 ± 0.50 s; P < 0.05) over a 500-m distance ( Hill et al., 2001 ).

The studies described above support the premise that canine and feline physiological and metabolic capabilities align with the preferred macronutrient levels of instinctual nutrition, which is particularly evident under physiological conditions of stress, such as aerobic exercise training. For cats, this also aligns with the macronutrient concentrations of ancestral nutrition. However, for dogs, ancestral nutrition specified by the diets of wolves is higher in protein and lower in fat and carbohydrates than preferences or physiology.

Further evidence is needed to support health benefits of natural diets for healthy, adult companion animals with maintenance requirements. There is a wide range of nutrient concentrations that may support optimal nutrition ( Kronfeld et al., 1994 ). When the effect of increasing a selected nutrient on some specific performance measure is determined, an optimal plateau is often observed before declining at yet higher concentrations. Furthermore, the optimal range of a nutrient is broader during undemanding physiological states, such as maintenance, but becomes narrower during states of physiological stress, such as growth or exercise training. This is evident in dogs' and cats' ability to effectively and safely use a wide range of macronutrient levels, including higher carbohydrate and lower fat or protein than those specified by instinctual or ancestral nutrition.

Adjusting macronutrient levels to provide optimal nutrition is particularly relevant considering modern pet lifestyles, in which companion animals live primarily indoors and are less active than their wild predecessors. Feeding management becomes a critical issue in feeding natural diets high in protein and fat to sedentary pets, given the substantial evidence for negative health effects of weight gain ( Lund et al., 2005 , 2006 ). Additionally, feeding foods containing high concentrations of animal based protein negatively impacts the environmental sustainability of a diet ( Reijnders and Soret, 2003 ). Including carbohydrate in pet foods aligns with the concept of nutritional sustainability by reducing the environmental impact of pet foods while supporting pet health and nutritional needs (for a complete review of this topic see Swanson et al., 2013 ). Partially meeting energy needs from carbohydrates while still meeting AA and fatty acid requirements allows for the moderate inclusion of more environmentally and economically costly protein and/or fat sources in a pet food, especially in cases where there is competition of certain sources for human food ingredients. Therefore, the potential health benefits of feeding natural diets, specific to an individual pet's lifestyle and health status, should be weighed against the potential health and environmental concerns of feeding a natural diet high in protein and fat Finally, where pet food manufacture is concerned, owner lifestyle must be matched against pet nutritional needs and feeding management. For example, some pets may be indoors for lengthy periods of time while owners are away. Therefore, physiologic patterns of defecation and urination may, of necessity, be different depending on a food's nutrient composition.

Whole Ingredients

Pet foods have historically been formulated based on nutrient content, given that animals have specific requirements for nutrients and not ingredients. However, in the natural pet food segment, there is an increased focus by consumers and pet food manufacturers on ingredients, especially whole ingredients. As it pertains to pet food ingredients, “whole” is defined as a physical form that is “complete, entire” ( AAFCO, 2013 ). Consequently, a growing trend for natural pet foods to contain more whole ingredients, such as meat instead of meat meals, whole grains instead of refined grains, and fruit and vegetable inclusions, has emerged ( Lummis, 2012 ).

The theory behind the beneficial health effects of whole ingredients is described by the concept of food synergy. Food synergy is based on the proposition that the action of the food matrix (i.e., the composite of naturally occurring food components) on biological systems is greater than or different from the corresponding actions of the individual food components ( Jacobs et al., 2009 ). It stems from the idea that we do not have complete knowledge of food composition and some health effects may result from unidentified or underappreciated components. In this way, whole ingredients may provide health benefits that the individual fractionated ingredients or single nutrients cannot provide. Although the term food synergy may not be well known by consumers, the concept of whole ingredients providing health benefits has likely contributed to the interest in natural pet foods by pet owners and hence the increased market demand for whole ingredients in pet foods.

The health benefit in humans of phytonutrients from fruits and vegetables is an example of food synergy. Epidemiological studies in humans indicate associations between fruit and vegetable intake with lower risk of cardiovascular disease in women ( Liu et al., 2000 ). In a human population study, consumption of foods rich in phytonutrients as measured by phytonutrient index has been shown to decrease weight gain and adiposity ( Mirmiran et al., 2012 ) and risk for metabolic syndrome ( Bahadoran et al., 2012 ). Rodent and in vitro models have shown positive effects of food synergy from fruits on antiproliferative and anticarcinogenic activities ( Jacobs et al., 2009 ). Drug-induced mammary tumor incidence in rats was reduced more by using the whole apple than only the flesh without the skin ( Liu et al., 2005 ). Similarly, whole pomegranates had greater in vitro antiproliferative effects than did some of their individual constituents ( Seeram et al., 2005 ). Importantly, as fruits and vegetables and their constituents are incorporated in pet foods, additional research is needed to understand the potential impact on pet health and well-being and the effect of processing on phytonutrient stability ( Tiwari and Cummins, 2013 ).

Whole grains are added to pet food formulations to provide digestible carbohydrates and dietary fiber ( de Godoy et al., 2013 ). The effects of whole grains as they relate to pet health and well-being have not been thoroughly evaluated. Of interest is that whole grains have greater concentrations of many nutrients, including fiber, vitamins, minerals, and phytonutrients, compared to refined grains ( Okarter and Liu, 2010 ; Jonnalagadda et al., 2011 ). For example, nutrient analysis of whole brown rice and brewers' rice used in pet food revealed higher ( P < 0.05) concentrations of ether extract fat, crude fiber, phosphorus, and potassium in whole brown rice compared to brewers' rice ( Table 1 ). This may seem irrelevant given that the dietary formulation of pet foods is intended to account for total nutrient needs especially when similar nutrient concentrations in can be achieved with supplemental fiber and synthetic vitamins and mineral source. However, as in fruits and vegetables, grains contain many unique phytonutrients. Recent studies by Forster et al. (2012a) demonstrated excellent digestibility and acceptability in dogs fed a dry-extruded diet when substituting some wheat and corn with 25% cooked navy bean powder while controlling both macronutrient and micronutrient contents. In addition, these workers also observed similar whole dry cooked bean powder containing diets to provide nutritional weight loss therapy while regulating serum lipids and biochemical analytes in overweight and obese dogs ( Forster et al., 2012b ). In humans, whole grain consumption has been associated with lower risk of certain cancers such as colon cancer. Phytonutrients, such as ferulic acid, have been implicated in the mechanism behind this lower risk ( Jonnalagadda et al., 2011 ). To date, this is an unexplored area for pet nutrition and additional studies are needed

Nutrient analysis (mean ± SD) of brewers' rice and whole brown rice

1 Independent t test.

The trend to include more whole ingredients in natural pet foods has also led to an increase in the inclusion of raw animal protein products as opposed to rendered animal protein products. Rendered products can have a wide range of nutritional variability, which is dependent on byproduct inclusion and processing of the product. For example, feed-grade poultry byproduct meal inclusive of feathers and heads had more variable nutrient content than pet-food grade poultry byproduct meal that did not contain feathers or heads ( Dozier et al., 2003 ). In a study using roosters to measure true AA digestibility, rendered animal meals generally had lower AA digestibility than raw animal products, with lamb meal having the poorest AA digestibility and pork livers (raw animal product) having the greatest AA digestibility ( Cramer et al., 2007 ). In a separate study, rendering of poultry, but not beef, seemed to have a slight negative influence on ileal, but not total tract, digestibility by dogs ( Murray et al., 1997 ). It should be noted, however, that handling, processing, and preservation by an ingredient supplier is a large contributor to the variability in nutritional value of animal products ( Parsons et al., 1997 ), and therefore ingredient supplier practices may be more important than ingredient type (i.e., raw vs. rendered) when assessing quality or nutritional value of animal products.

Ingredient and Product Processing

Processing can have either a positive or negative effect on nutritional value, depending on the processing method and outcomes measured. For example, the degree of gelatinization of wheat starch is positively associated with in vitro digestibility and plasma glucose and insulin responses in rats ( Holm et al., 1988 ), indicating increased digestible carbohydrate bioavailability with processing. Additionally, starch gelatinization degree and reactive lysine in a canine diet increased with increasing extrusion temperatures up to 150°C compared to untreated control ( Lankhorst et al., 2007 ). Conversely, increasing time of heat treatment during canning of cat food was associated with a decrease in true ileal AA digestibility in rats ( Hendriks et al., 1999 ). Higher drying temperatures (200°C) of an extruded canine diet resulted in lower lysine, reactive lysine, reactive to total lysine ratio, linolenic acid, and linoleic acid concentrations compared to lower drying temperatures (≤160°C) in 4 mm kibbles ( Tran et al., 2011 ). These examples of processing influencing the quality and nutritional value of an ingredient or final product highlight the importance of quality control outcomes in ingredient selection and final product processing.

Processing method also influences nutritional value by affecting the moisture content of the final product. From a nutritional perspective, foods with moisture content similar to animal prey would better align with a natural pet nutrition philosophy compared to dry foods. While there is limited evidence to demonstrate a health benefit of high dietary moisture intake in dogs, there have been demonstrated effects in cats on urinary tract health and weight management. Feeding diets containing 73% moisture reduced ( P < 0.05) the calcium oxalate relative super saturation from 1.14 ± 0.21 compared with the 6 (2.29 ± 0.21) and 53% (2.06 ± 0.21) moisture diets and reduced ( P < 0.001) specific gravity from 1.036 ± 0.002 compared with the 6, 25, and 53% moisture diets (1.052–1.054 ± 0.002) while increasing ( P < 0.001) total water intake of cats to 144.7 ± 5.2 mL compared with diets containing 6, 25, or 53% moisture (98.6–104.7 ± 5.3 mL; Buckley et al., 2011 ). Another study found that ad libitum ingestion of a 40% hydrated diet compared to a dry diet with 12% moisture following weight loss caused cats to eat less (77 ± 10.8 vs. 86 ± 18.4 g/d; P < 0.05), with a trend to gain less BW (312 ± 95.9 g vs. 368 ± 120.7 g; P = 0.28), and increased their activity level ( P < 0.001; Cameron et al., 2011 ). Although these findings may be specific to the diets evaluated, given the ubiquitous nature of urinary related syndromes in cats, the potential health benefits of feeding pet food with higher moisture content (e.g., pasteurized/refrigerated, raw, frozen, or canned) that typically contain 70 to 85% moisture should be noted.

There are reports in the literature evaluating the digestibility of raw diets in feline species that have been discussed above. However, Kerr et al. (2012) evaluated the performance of extruded cat food versus a beef based diet fed either raw or cooked. These investigators found the apparent total tract digestibility to be greater ( P < 0.001) in both the raw and cooked form of the beef based diet than the extruded diet. There were no differences in apparent digestibility between the raw and cooked beef based diet. The differences observed in this study could be due to the ingredient composition as well as processing method. Given the level of ingredient processing required before extrusion, it would be difficult to design a study using ingredients in the same physical form with and without extrusion.

Processing method is also an important influencer of food safety. With respect to food processing, unpasteurized raw foods would most closely match wild prey and therefore align with a natural pet nutrition philosophy. However, there are safety concerns with the pathogenic bacteria found in many raw meats. Studies have demonstrated that raw or undercooked animal-source protein may be contaminated with a variety of pathogenic organisms, including Salmonella spp., Campylobacter spp., Clostridium spp., Escherichia coli , Listeria monocytogenes , and enterotoxigenic Staphylococcus aureus ( Freeman and Michel, 2001 ; LeJeune and Hancock, 2001 ; Joffe and Schlesinger, 2002 ; Stiver et al., 2003 ; Weese et al., 2005 ; Finley et al., 2006 ). In a cohort of 200 therapy dogs, the incidence rate of Salmonella shedding in the raw meat-fed dogs was 0.61 cases/dog–year, compared with 0.08 cases/dog–year in dogs that were not fed raw meat ( P < 0.001; Lefebvre et al., 2008 ). This poses a risk of foodborne illness to the pets eating the contaminated food and of secondary transmission to humans, especially children, older persons, and immunocompromised individuals ( LeJeune and Hancock, 2001 ; Joffe and Schlesinger, 2002 ). Given these health risks, the American Veterinary Medical Association, American Animal Hospital Association, and U.S. Food and Drug Administration have issued statements on the avoidance and safe handling practices of raw foods ( AAHA, 2011 ; AVMA, 2012a ; FDA, 2013 ). The American College of Veterinary Nutrition also has endorsed a publication on the potential risks vs. benefits of pets consuming raw meat based diets ( Freeman et al., 2013 ). Furthermore, raw food diets can pose risk for metabolic disease depending on the parts of the animal used in the diet. For example, clinical cases of dietary hyperthyroidism have been reported in dogs fed bone and raw food diets, which was reversed by feeding commercial pet food ( Kohler et al., 2012 ). To reduce safety concerns, minimal processing may be applied, such as pasteurization of raw animal products, or comprehensive microbiological testing of product may be used.

The natural segment of manufactured pet food has grown in recent years driven by consumer demand. The increased demand for these products has centered on the consumer belief that these products are of high quality and safe, made from ingredients that fit an individual's concept of natural, and provide functional health benefits. Different regulatory definitions have been described by the AAFCO and FEDIAF for natural pet food ingredients and products; however, most consumers have their own perceptions of what should be considered natural based on personal experiences, biases, or preferences. In the absence of data on the impact of natural pet food on pet health, some pet food companies target diet formulation and ingredients based on teleological reasoning that dogs and cats should eat a diet resembling that of related wild species. Many opportunities exist for research involving natural pet foods and natural diets to understand their effects on growth and performance, nutrient availability, digestibility, and product safety among other health and nutrition parameters. Future opportunities also include the integration of sustainability with natural pet foods ( Swanson et al., 2013 ). The challenge is to match consumer demand and provide natural nutrition to pets while reducing impact on the environment. With the increasing trend of anthropomorphism of pets and interest in ancestral or instinctual diets, challenges of particular interest to the natural pet food segment include competition with the human food chain and the high use of animal protein sources.

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Nutrition, Food and Diet in Health and Longevity: We Eat What We Are

Suresh i. s. rattan.

1 Department of Molecular Biology and Genetics, Aarhus University, 8000 Aarhus, Denmark

Gurcharan Kaur

2 Department of Biotechnology, Guru Nanak Dev University, Amritsar 143005, India

Associated Data

Not applicable.

Nutrition generally refers to the macro- and micro-nutrients essential for survival, but we do not simply eat nutrition. Instead, we eat animal- and plant-based foods without always being conscious of its nutritional value. Furthermore, various cultural factors influence and shape our taste, preferences, taboos and practices towards preparing and consuming food as a meal and diet. Biogerontological understanding of ageing has identified food as one of the three foundational pillars of health and survival. Here we address the issues of nutrition, food and diet by analyzing the biological importance of macro- and micro-nutrients including hormetins, discussing the health claims for various types of food, and by reviewing the general principles of healthy dietary patterns, including meal timing, caloric restriction, and intermittent fasting. We also present our views about the need for refining our approaches and strategies for future research on nutrition, food and diet by incorporating the molecular, physiological, cultural and personal aspects of this crucial pillar of health, healthy ageing and longevity.

1. Introduction

The terms nutrition, food and diet are often used interchangeably. However, whereas nutrition generally refers to the macro- and micro-nutrients essential for survival, we do not simply eat nutrition, which could, in principle, be done in the form of a pill. Instead, we eat food which normally originates from animal- and plant-based sources, without us being aware of or conscious of its nutritional value. Even more importantly, various cultural factors influence and shape our taste, preferences, taboos and practices towards preparing and consuming food as a meal and diet [ 1 ]. Furthermore, geo-political-economic factors, such as governmental policies that oversee the production and consumption of genetically modified foods, geological/climatic challenges of growing such crops in different countries, and the economic affordability of different populations for such foods, also influence dietary habits and practices [ 2 , 3 ]. On top of all this lurks the social evolutionary history of our species, previously moving towards agriculture-based societies from the hunter-gatherer lifestyle, now becoming the consumers of industrially processed food products that affect our general state of health, the emergence of diseases, and overall lifespan [ 1 , 4 ]. The aim of this article is to provide a commentary and perspective on nutrition, food and diet in the context of health, healthy ageing and longevity.

Biogerontological understanding of ageing has identified food as one of the three foundational pillars of health and survival. The other two pillars, especially in the case of human beings, are physical exercise and socio-mental engagement [ 5 , 6 , 7 ]. A huge body of scientific and evidence-based information has been amassed with respect to the qualitative and quantitative nature of optimal nutrition for human health and survival. Furthermore, a lot more knowledge has developed regarding how different types of foods provide different kinds of nutrition to different extents, and how different dietary practices have either health-beneficial or health-harming effects.

Here we endeavor to address these issues of nutrition, food and diet by analyzing the biological importance of macro- and micro-nutrients, and by discussing the health-claims about animal-based versus plant-based foods, fermented foods, anti-inflammatory foods, functional foods, foods for brain health, and so on. Finally, we discuss the general principles of healthy dietary patterns, including the importance of circadian rhythms, meal timing, chronic caloric restriction (CR), and intermittent fasting for healthy ageing and extended lifespan [ 8 , 9 ]. We also present our views about the need for refining our approaches and strategies for future research on nutrition, food and diet by incorporating the molecular, physiological, cultural and personal aspects of this crucial pillar of health, healthy ageing and longevity.

2. Nutrition for Healthy Ageing

The science of nutrition or the “nutritional science” is a highly advanced field of study, and numerous excellent books, journals and other resources are available for fundamental information about all nutritional components [ 10 ]. Briefly, the three essential macronutrients which provide the basic materials for building biological structures and for producing energy required for all physiological and biochemical processes are proteins, carbohydrates and lipids. Additionally, about 18 micronutrients, comprised of minerals and vitamins, facilitate the optimal utilization of macronutrients via their role in the catalysis of numerous biochemical processes, in the enhancement of their bioavailability and absorption, and in the balancing of the microbiome. Scientific literature is full of information about almost all nutritional components with respect to their importance and role in basic metabolism for survival and health throughout one’s life [ 10 ].

In the context of ageing, a major challenge to maintain health in old age is the imbalanced nutritional intake resulting into nutritional deficiency or malnutrition [ 11 , 12 ]. Among the various reasons for such a condition is the age-related decline in the digestive and metabolic activities, exacerbated by a reduced sense of taste and smell and worsening oral health, including the ability to chew and swallow [ 13 , 14 ]. Furthermore, an increased dependency of the older persons on medications for the management or treatment of various chronic conditions can be antagonistic to certain essential nutrients. For example, long term use of metformin, which is the most frequently prescribed drug against Type 2 diabetes, reduces the levels of vitamin B12 and folate in the body [ 15 , 16 ]. Some other well-known examples of the drugs used for the management or treatment of age-related conditions are cholesterol-lowering medicine statin which can cause coenzyme Q10 levels to be too low; various diuretics (water pills) can cause potassium levels to be too low; and antacids can decrease the levels of vitamin B12, calcium, magnesium and other minerals [ 15 , 16 ]. Thus, medications used in the treatment of chronic diseases in old age can also be “nutrient wasting” or “anti-nutrient” and may cause a decrease in the absorption, bioavailability and utilization of essential micronutrients and may have deleterious effects to health [ 11 ]. In contrast, many nutritional components have the potential to interact with various drugs leading to reduced therapeutic efficacy of the drug or increased adverse effects of the drug, which can have serious health consequences. For example, calcium in dairy products like milk, cheese and yoghurt can inhibit the absorption of antibiotics in the tetracycline and quinolone class, thus compromising their ability to treat infection effectively. Some other well-known examples of food sources which can alter the pharmacokinetics and pharmacodynamics of various drugs are grape fruits, bananas, apple juice, orange juice, soybean flour, walnuts and high-fiber foods (see: https://www.aarp.org/health/drugs-supplements/info-2022/food-medication-interaction.html (accessed on 13 November 2022)).

It is also known that the nutritional requirements of older persons differ both qualitatively and quantitatively from young adults [ 11 ]. This is mainly attributed to the age-related decline in the bioavailability of nutrients, reduced appetite, also known as ‘anorexia of ageing,’ as well as energy expenditure [ 12 , 17 , 18 ]. Therefore, in order to maintain a healthy energy balance, the daily uptake of total calories may need to be curtailed without adversely affecting the nutritional balance. This may be achieved by using nutritional supplements with various vitamins, minerals and other micronutrients, without adding to the burden of total calories [ 12 , 17 , 18 ]. More recently, the science of nutrigenomics (how various nutrients affect gene expression), and the science of nutrigenetics (how individual genetic variations respond to different nutrients) are generating novel and important information on the role of nutrients in health, survival and longevity.

3. Food for Healthy Ageing

The concept of healthy ageing is still being debated among biogerontologists, social-gerontologists and medical practioners. It is generally agreed that an adequate physical and mental independence in the activities of daily living can be a pragmatic definition of health in old age [ 7 ]. Thus, healthy ageing can be understood as a state of maintaining, recovering and enhancing health in old age, and the foods and dietary practices which facilitate achieving this state can be termed as healthy foods and diets.

From this perspective, although nutritional requirements for a healthy and long life could be, in principle, fulfilled by simply taking macro- and micro-nutrients in their pure chemical forms, that is not realistic, practical, attractive or acceptable to most people. In practice, nutrition is obtained by consuming animals and plants as sources of proteins, carbohydrates, fats and micronutrients. There is a plethora of tested and reliable information available about various food sources with respect to the types and proportion of various nutrients present in them. However, there are still ongoing discussions and debates as to what food sources are best for human health and longevity [ 19 , 20 ]. Often such discussions are emotionally highly charged with arguments based on faith, traditions, economy and, more recently, on political views with respect to the present global climate crisis and sustainability.

Scientifically, there is no ideal food for health and longevity. Varying agricultural and food production practices affect the nutritional composition, durability and health beneficial values of various foods. Furthermore, the highly complex “science of cooking” [ 21 ], evolved globally during thousands of years of human cultural evolution, has discovered the pros and cons of food preparation methods such as soaking, boiling, frying, roasting, fermenting and other modes of extracting, all with respect to how best to use these food sources for increasing the digestibility and bioavailability of various nutrients, as well as how to eliminate the dangers and toxic effects of other chemicals present in the food.

The science of food preparation and utilization has also discovered some paradoxical uses of natural compounds, especially the phytochemicals such as polyphenols, flavonoids, terpenoids and others. Most of these compounds are produced by plants as toxins in response to various stresses, and as defenses against microbial infections [ 22 , 23 ]. However, humans have discovered, mostly by trial and error, that numerous such toxic compounds present in algae, fungi, herbs and other sources can be used in small doses as spices and condiments with potential benefits of food preservation, taste enhancement and health promotion [ 23 ].

The phenomenon of “physiological hormesis” [ 24 ] is a special example of the health beneficial effects of phytotoxins. According to the concept of hormesis, a deliberate and repeated use of low doses of natural or synthetic toxins in the food can induce one or more stress responses in cells and tissues, followed by the stimulation of numerous defensive repair and maintenance processes [ 25 , 26 ]. Such hormesis-inducing compounds and other conditions are known as hormetins, categorized as nutritional, physical, biological and mental hormetins [ 27 , 28 , 29 ]. Of these, nutritional hormetins, present naturally in the food or as synthetic hormetins to be used as food supplements, are attracting great attention from food-researchers and the nutraceutical and cosmeceutical industry [ 27 , 30 ]. Other food supplements being tested and promoted for health and longevity are various prebiotics and probiotics strengthening and balancing our gut microbiota [ 31 , 32 , 33 ].

Recently, food corporations in pursuit of both exploiting and creating a market for healthy ageing products, have taken many initiatives in producing new products under the flagship of nutraceuticals, super-foods, functional foods, etc. Such products are claimed and marketed not only for their nutritional value, but also for their therapeutic potentials [ 10 ]. Often the claims for such foods are hyped and endorsed as, for example, anti-inflammatory foods, food for the brain, food for physical endurance, complete foods, anti-ageing foods and so on [ 34 , 35 , 36 ]. Traditional foods enriched with a variety of minerals, vitamins and hormetins are generally promoted as “functional foods” [ 37 ]. Even in the case of milk and dairy products, novel and innovative formulations are claimed to improve their functionality and health promotional abilities [ 38 ]. However, there is yet a lot to be discovered and understood about such reformulated, fortified and redesigned foods with respect to their short- and long-term effects on physiology, microbiota balance and metabolic disorders in the context of health and longevity.

4. Diet and Culture for Healthy and Long Life

What elevates food to become diet and a meal is the manner and the context in which that food is consumed [ 4 ]. Numerous traditional and socio-cultural facets of dietary habits can be even more significant than their molecular, biochemical, and physiological concerns regarding their nutritional ingredients and composition. For example, various well-known diets, such as the paleo, the ketogenic, the Chinese, the Ayurvedic, the Mediterranean, the kosher, the halal, the vegetarian, and more recently, the vegan diet, are some of the diverse expressions of such cultural, social, and political practices [ 1 ]. The consequent health-related claims of such varied dietary patterns have influenced their acceptance and adaptation globally and cross-culturally.

Furthermore, our rapidly developing understanding about how biological daily rhythms affect and regulate nutritional needs, termed “chrono-nutrition”, has become a crucial aspect of optimal and healthy eating habits [ 39 , 40 ]. A similar situation is the so-called “nutrient timing” that involves consuming food at strategic times for achieving certain specific outcomes, such as weight reduction, muscle strength, and athletic performance. The meal-timing and dietary patterns are more anticipatory of health-related outcomes than any specific foods or nutrients by themselves [ 41 , 42 , 43 , 44 ]. However, encouraging people to adopt healthy dietary patterns and meal-timing requires both the availability, accessibility and affordability of food, and the intentional, cultural and behavioral preferences of the people.

Looking back at the widely varying and constantly changing cultural history of human dietary practices, one realizes that elaborate social practices, rituals and normative behaviors for obtaining, preparing and consuming food, are often more critical aspects of health-preservation and health-promotion than just the right combination of nutrients. Therefore, one cannot decide on a universal food composition and consumption pattern ignoring the history and the cultural practices and preferences of the consumers. After all, “we eat what we are”, and not, as the old adage says, “we are what we eat”.

5. Conclusions and Perspectives

Food is certainly one of the foundational pillars of good and sustained health. Directed and selective evolution through agricultural practices and experimental manipulation and modification of food components have been among the primary targets for improving food quality. This is further authenticated by extensive research performed, mainly on experimental animal and cell culture model systems, demonstrating the health-promoting effects of individual nutritional components and biological extracts in the regulation, inhibition or stimulation of different molecular pathways with reference to healthy ageing and longevity [ 45 ]. Similarly, individual nutrients or a combination of a few nutrients are being tested for their potential use as calorie restriction mimetics, hormetins and senolytics [ 46 , 47 , 48 ]. However, most commonly, these therapeutic strategies follow the traditional “one target, one missile” pharmaceutical-like approach, and consider ageing as a treatable disease. Based on the results obtained from such experimental studies, the claims and promises made which can often be either naïve extrapolations from experimental model systems to human applications, or exaggerated claims and even false promises [ 49 ].

Other innovative, and possibly holistic, food- and diet-based interventional strategies for healthy ageing are adopting regimens such as caloric- and dietary-restriction, as well as time-restricted eating (TRE). Intermittent fasting (IF), the regimen based on manipulating the eating/fasting timing, is another promising interventional strategy for healthy ageing. Chrono-nutrition, which denotes the link between circadian rhythms and nutrient-sensing pathways, is a novel concept illustrating how meal timings alignment with the inherent molecular clocks of the cells functions to preserve metabolic health. TRE, which is a variant of the IF regimen, claims that food intake timing in alignment with the circadian rhythm is more beneficial for health and longevity [ 39 , 40 , 41 , 50 ]. Moreover, TRE has translational benefits and is easy to complete in the long term as it only requires limiting the eating time to 8–10 h during the day and the fasting window of 12–16 h without restricting the amount of calories consumed. Some pilot studies on the TRE regimen have reported improvement in glucose tolerance and the management of body weight and blood pressure in obese adults as well as men at risk of T2D. Meta-analyses of several pilot scale studies in human subjects suggest and support the beneficial effects of a TRE regimen on several health indicators [ 39 , 50 ]. Several other practical recommendations, based on human clinical trials have also been recommended for meeting the optimal requirements of nutrition in old age, and for preventing or slowing down the progression of metabolic syndromes [ 39 , 40 , 41 , 50 ].

What we have earlier discussed in detail [ 4 ] is supported by the following quote: “…food is more than just being one of the three pillars of health. Food is both the foundation and the scaffolding for the building and survival of an organism on a daily basis. Scientific research on the macro- and micro-nutrient components of food has developed deep understanding of their molecular, biochemical and physiological roles and modes of action. Various recommendations are repeatedly made and modified for some optimal daily requirements of nutrients for maintaining and enhancing health, and for the prevention and treatment of diseases. Can we envisage developing a “nutrition pill” for perfect health, which could be used globally, across cultures, and at all ages? We don’t think so” [ 4 ].

Our present knowledge about the need and significance of nutrients is mostly gathered from the experimental studies using individual active components isolated from various food sources. In reality, however, these nutritional components co-exist interactively with numerous other compounds, and often become chemically modified through the process of cooking and preservation, affecting their stability and bioavailability. There is still a lot to be understood about how the combination of foods, cooking methods and dietary practices affect health-related outcomes, especially with respect to ageing and healthspan.

An abundance of folk knowledge in all cultures about food-related ‘dos and don’ts’ requires scientific verification and validation. We also need to reconsider and change our present scientific protocols for nutritional research, which seem to be impractical for food and dietary research at the level of the population. It is a great scientific achievement that we have amassed a body of information with respect to the nature of nutritional components required for health and survival, the foods which can provide those nutritional components and the variety of dietary and eating practices which seem to be optimal for healthy survival and longevity.

Finally, whereas abundant availability of and accessibility to food in some parts of the world has led to over-consumption and consequent life-style-induced metabolic diseases and obesity, in many other parts of the world food scarcity and economic disparity continue to perpetuate starvation, malnutrition, poor health and shortened lifespan. Often, it is not a lack of knowledge about the optimal nutrition, food and diet that leads to making bad choices; rather, it is either our inability to access and afford healthy foods or our gullibility to fall prey to the exaggerated claims in the commercial interests of food producing and marketing companies. We must continue to gather more scientific information and knowledge about the biochemical, physiological and cultural aspects of nutrition, food and diet, which should then be recommended and applied wisely and globally, incorporating the social, cultural and environmental needs of all. After all, “we eat what we are”, and not merely “we are what we eat”!

Funding Statement

One of the authors, GK, was funded by the Department of Science & Technology (DST) under Cognitive Science Research Initiative (CSRI), Government of India, grant (DST/CSRI/2018/99). This funding agency has no role in study design, manuscript writing, and data interpretation.

Author Contributions

Both authors (S.I.S.R. and G.K.) conceptualized and wrote the paper equally. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Informed consent statement, data availability statement, conflicts of interest.

The authors declare no conflict of interest.

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