write a term paper on digestion and absorption of lipids

Digestion and Absorption of Lipids

Lipid digestion and absorption pose some special challenges. Triglycerides are large molecules, and unlike carbohydrates and proteins, they’re not water-soluble. Because of this, they like to cluster together in large droplets when they’re in a watery environment like the digestive tract. The digestive process has to break those large droplets of fat into smaller droplets and then enzymatically digest lipid molecules using enzymes called lipases . The mouth and stomach play a small role in this process, but most enzymatic digestion of lipids happens in the small intestine. From there, the products of lipid digestion are absorbed into circulation and transported around the body, which again requires some special handling since lipids are not water-soluble and do not mix with the watery blood.

5 middle-aged women eating ice cream, dressed in running clothes

Let’s start at the beginning to learn more about the path of lipids through the digestive tract.

1. Lipid Digestion in the Mouth

A few things happen in the mouth that start the process of lipid digestion. Chewing mechanically breaks food into smaller particles and mixes them with saliva. An enzyme called lingual lipase is produced by cells on the tongue (“lingual” means relating to the tongue) and begins some enzymatic digestion of triglycerides, cleaving individual fatty acids from the glycerol backbone.

2. Lipid Digestion in the Stomach

In the stomach, mixing and churning helps to disperse food particles and fat molecules. Cells in the stomach produce another lipase, called gastric lipase (“gastric” means relating to the stomach) that also contributes to enzymatic digestion of triglycerides. Lingual lipase swallowed with food and saliva also remains active in the stomach. But together, these two lipases play only a minor role in fat digestion (except in the case of infants, as explained below), and most enzymatic digestion happens in the small intestine.

Cartoon diagram showing the organs of the gastrointestinal tract and the steps of lipid digestion that occur in each organ. In the mouth: mechanical digestion, mixing with saliva, and limited enzymatic digestion (lingual lipase). In the stomach: mixing/churning, limited enzymatic digestion (gastric lipase). In the small intestine: emulsification (bile), enzymatic digestion (pancreatic lipases), micelles help with absorption.

Figure 5.21. Overview of lipid digestion in the human gastrointestinal tract.

3. Lipid Digestion in the Small Intestine

As the stomach contents enter the small intestine, most of the dietary lipids are undigested and clustered in large droplets. Bile , which is made in the liver and stored in the gallbladder, is released into the duodenum, the first section of the small intestine. Bile salts have both a hydrophobic and a hydrophilic side, so they are attracted to both fats and water. This makes them effective emulsifiers, meaning that they break large fat globules into smaller droplets. Emulsification makes lipids more accessible to digestive enzymes by increasing the surface area for them to act (see Fig. 5.22 below).

The pancreas secretes pancreatic lipases into the small intestine to enzymatically digest triglycerides. Triglycerides are broken down to fatty acids, monoglycerides (glycerol backbone with one fatty acid still attached), and some free glycerol. Cholesterol and fat-soluble vitamins do not need to be enzymatically digested (see Fig. 5.22 below).

4. Lipid Absorption from the Small Intestine

Next, those products of fat digestion (fatty acids, monoglycerides, glycerol, cholesterol, and fat-soluble vitamins) need to enter into the circulation so that they can be used by cells around the body. Again, bile helps with this process. Bile salts cluster around the products of fat digestion to form structures called micelles , which help the fats get close enough to the microvilli of intestinal cells so that they can be absorbed. The products of fat digestion diffuse across the membrane of the intestinal cells, and bile salts are recycled back to do more work emulsifying fat and forming micelles.

A cartoon diagram summarizes the steps of emulsification, enzymatic digestion, and absorption of lipids in the small intestine. The diagram shows large fat droplets being emulsified to smaller droplets, then being incorporated into micelles in order to bring them to the edge of the enterocytes. Then, fatty acids are absorbed into the enterocytes and incorporated into chylomicrons in the golgi of the cell, finally being absorbed into the lacteal to enter the lymph.

Figure 5.22. Lipid digestion and absorption in the small intestine.

Once inside the intestinal cell, short- and medium-chain fatty acids and glycerol can be directly absorbed into the bloodstream, but larger lipids such as long-chain fatty acids, monoglycerides, fat-soluble vitamins, and cholesterol need help with absorption and transport to the bloodstream. Long-chain fatty acids and monoglycerides reassemble into triglycerides within the intestinal cell, and along with cholesterol and fat-soluble vitamins, are then incorporated into transport vehicles called chylomicrons. Chylomicrons are large structures with a core of triglycerides and cholesterol and an outer membrane made up of phospholipids, interspersed with proteins (called apolipoproteins) and cholesterol. This outer membrane makes them water-soluble so that they can travel in the aqueous environment of the body. Chylomicrons from the small intestine travel first into lymph vessels, which then deliver them to the bloodstream.

Chylomicrons are one type of lipoprotein—transport vehicles for lipids in blood and lymph. We’ll learn more about other types of lipoproteins on the next page.

Cartoon diagram showing the structure of a chylomicron. The interior is stuffed with triglycerides, shown in light yellow. The exterior is made up of phospholipids, shown in white and oriented with their fatty tails towards the inside of the chylomicron, and dotted with embedded apolipoproteins, shown in blue.

Figure 5.23. Structure of a chylomicron. Cholesterol is not shown in this figure, but chylomicrons contain cholesterol in both the lipid core and embedded on the surface of the structure.

VIDEO: “Lipids —Digestion and Absorption,” by Alice Callahan, YouTube (November, 17, 2019), 8:49 minutes.

Special Adaptations for Lipid Digestion in Infants

Lipids are an important part of an infant’s diet. Breast milk contains about 4 percent fat, similar to whole cow’s milk. Whether breastfed or formula-fed, fat provides about half of an infant’s calories, and it serves an important role in brain development. Yet, infants are born with low levels of bile and pancreatic enzyme secretion, which are essential contributors to lipid digestion in older children and adults. So, how do babies digest all of the fat in their diet?

Infants have a few special adaptations that allow them to digest fat effectively. First, they have plenty of lingual and gastric lipases right from birth. These enzymes play a much more important role in infants than they do in adults. Second, breast milk actually contains lipase enzymes that are activated in the baby’s small intestine. In other words, the mother makes lipases and sends them in breast milk to help her baby digest the milk fats. Amazing, right? Between increased activity of lingual and gastric lipases and the lipases contained in breast milk, young infants can efficiently digest fat and reap its nutritional value for growth and brain development. Studies show that fat digestion is more efficient in premature infants fed breast milk compared with those fed formula. Even pasteurized breast milk, as is used when breast milk is donated for feeding babies in the hospital, is a little harder to digest, because heat denatures the lipases. (Infants can still digest pasteurized breast milk and formula; they’re just less efficient at doing so and absorb less of the products of triglyceride digestion.) 1

A mother is shown lying comfortably on her side, head propped up by a pillow, with her baby lying next to her and breastfeeding. Mother and baby are making eye contact.

Self-Check:

References:

Lindshield, B. L. Kansas State University Human Nutrition (FNDH 400) Flexbook. goo.gl/vOAnR
OpenStax, Anatomy and Physiology. OpenStax CNX. Aug 28, 2019 http://cnx.org/contents/[email protected] .
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program, “Digestion and Absorption of Lipids ,” CC BY-NC 4.0
1 American Academy of Pediatrics Committee on Nutrition, 2014. Chapter 2: Development of Gastrointestinal Function. In: Kleinman RE, Greer FR, eds. Pediatric Nutrition. 7th ed. Elk Grove Village, IL: American Academy of Pediatrics.

Image Credits:

“all eating ice cream” by salem elizabeth is licensed under CC BY 2.0
Figure 5.21. “Overview of lipid digestion” by Alice Callahan is licensed under CC BY 4.0 ; edited from “Digestive system diagram edit” by Mariana Ruiz, edited by Joaquim Alves Gaspar, Jmarchn is in the Public Domain
Figure 5.22. “Lipid digestion and absorption in the small intestine” by Alice Callahan is licensed under CC BY 4.0 ; edited from “Lipid Absorption” by OpenStax is licensed under CC BY 4.0
Figure 5.23. “Chylomicrons Contain Triglycerides Cholesterol Molecules and Other Lipids” by OpenStax College, Anatomy & Physiology, Connexions Web site is licensed under CC BY 3.0
“IMGP1686” (breastfeeding baby) by Celeste Burke is licensed under CC BY 2.0

A group of enzymes that facilitate the chemical breakdown of triglycerides.

An enzyme produced by cells on the tongue; begins the chemical breakdown of triglycerides.

An enzyme produced by cells of the stomach; aids in the chemical breakdown of triglycerides.

A chemical made by the liver and stored in the gallbladder; acts as an emulsifier, which allows fat droplets to mix with the watery digestive juices in the small intestine.

Enzymes produced by the pancreas; chemically break down triglycerides in the small intestine.

Structures that consist of bile salts clustered around the products of fat digestion; aid in absorption of fats into enterocytes.

A type of lipoprotein that serves as a transport vehicle for lipids absorbed from the small intestine into lymph and blood.

Nutrition: Science and Everyday Application, v. 1.0 Copyright © 2020 by Alice Callahan, PhD; Heather Leonard, MEd, RDN; and Tamberly Powell, MS, RDN is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Digestion and Absorption of Lipids

First Online: 30 December 2018

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write a term paper on digestion and absorption of lipids

Anil Gupta 2

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Lipids are important source of energy for living organisms. A healthy adult person requires around 2800 calories per day. It is recommended that around 20–35% of daily calories should be furnished by dietary lipids. Calorific value of fats is (9 calories/g). An adult person should consume around 60–90 g of fats per day. Intake of calories from saturated fatty acids and trans fatty acids should be <10% and 2% of total calories, respectively, per day.

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Department of Physiology and Biochemistry, Eklavya Dental College and Hospital, Kotputli, Rajasthan, India

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Gupta, A. (2019). Digestion and Absorption of Lipids. In: Comprehensive Biochemistry for Dentistry. Springer, Singapore. https://doi.org/10.1007/978-981-13-1035-5_16

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Unit 5 – Lipids: Fats, Oils, and Cholesterol

5.5 Digestion and Absorption of Lipids

Let’s start at the beginning to learn more about the path of lipids through the digestive tract.

1. Lipid Digestion in the Mouth

Chewing mechanically breaks food into smaller particles and mixes them with saliva. An enzyme called lingual lipase is produced by cells on the tongue (“lingual” means relating to the tongue) and begins some enzymatic digestion of triglycerides, cleaving individual fatty acids from the glycerol backbone.

2. Lipid Digestion in the Stomach

In the stomach, mixing and churning helps disperse food particles and fat molecules. Cells in the stomach produce another lipase, called gastric lipase (“gastric” means relating to the stomach) that also contributes to enzymatic digestion of triglycerides. Lingual lipase swallowed with food and saliva also remains active in the stomach. But together, these two lipases play only a minor role in fat digestion (except in the case of infants, as explained below), and most enzymatic digestion happens in the small intestine.

3. Lipid Digestion in the Small Intestine

4. Lipid Absorption from the Small Intestine

Chylomicrons are large structures with a core of triglycerides and cholesterol and an outer membrane made up of phospholipids, interspersed with proteins (called apolipoproteins) and cholesterol. This outer membrane makes them water-soluble so that they can travel in the aqueous environment of the body. Chylomicrons from the small intestine travel first into lymph vessels, which then deliver them to the bloodstream.

Chylomicrons are one type of lipoprotein—transport vehicles for lipids in blood and lymph. We’ll learn more about other types of lipoproteins on the next page.

VIDEO: “Lipids —Digestion and Absorption,” by Alice Callahan, YouTube (November, 17, 2019), 8:49 minutes.

Special Adaptations for Lipid Digestion in Infants

Review Questions

Attributions:.

Lane Community College’s Nutrition: Science and Everyday Application “ Classification of Nutrients ” CC BY-NC 4.0

References:

Lindshield, B. L. Kansas State University Human Nutrition (FNDH 400) Flexbook. goo.gl/vOAnR
OpenStax, Anatomy and Physiology. OpenStax CNX. Aug 28, 2019 http://cnx.org/contents/[email protected] .
University of Hawai‘i at Mānoa Food Science and Human Nutrition Program, “Digestion and Absorption of Lipids ,” CC BY-NC 4.0
1 American Academy of Pediatrics Committee on Nutrition, 2014. Chapter 2: Development of Gastrointestinal Function. In: Kleinman RE, Greer FR, eds. Pediatric Nutrition. 7th ed. Elk Grove Village, IL: American Academy of Pediatrics.

Image Credits:

“all eating ice cream” by salem elizabeth is licensed under CC BY 2.0
Figure 5.21. “Overview of lipid digestion” by Alice Callahan is licensed under CC BY 4.0 ; edited from “Digestive system diagram edit” by Mariana Ruiz, edited by Joaquim Alves Gaspar, Jmarchn is in the Public Domain
Figure 5.22. “Lipid digestion and absorption in the small intestine” by Alice Callahan is licensed under CC BY 4.0 ; edited from “Lipid Absorption” by OpenStax is licensed under CC BY 4.0
Figure 5.23. “Chylomicrons Contain Triglycerides Cholesterol Molecules and Other Lipids” by OpenStax College, Anatomy & Physiology, Connexions Web site is licensed under CC BY 3.0
“IMGP1686” (breastfeeding baby) by Celeste Burke is licensed under CC BY 2.0

Introduction to Nutrition and Wellness Copyright © 2022 by Janet Colson; Sandra Poirier; and Yvonne Dadson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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6.3 Lipid Digestion, Absorption, and Transport

Lipids are large molecules and generally are not water-soluble. Like carbohydrates, lipids are broken into small components for absorption. The main goal of lipid digestion is to remove fatty acids from the glycerol backbone using the enzyme lipase. However, lipid digestion is more complicated than carbohydrate digestion because most of our digestive tract and digestive enzymes are water based. Figure 6.13 shows a general overview of what happens to lipids at each part of the digestive tract. Each step is described in more detail below.

Figure 6.13 Overview of Lipid Digestion, Absorption, and Transport

Diagram showing the organs of the digestive system and their functions for lipid digestion.

From the Mouth to the Stomach

The first step in the digestion of triglycerides and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components.

In the stomach, gastric lipase starts to break down triglycerides into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triglycerides are converted to diglycerides and fatty acids. The stomach’s churning and contractions help to disperse the fat molecules, while the diglycerides derived in this process act as further emulsifiers. However, even amid all of this activity, very little fat digestion occurs in the stomach.

Entering the Bloodstream

As stomach contents enter the small intestine, the digestive system sets out to manage a small hurdle, namely, to combine the separated fats with its own watery fluids. The solution to this hurdle is bile. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier. It attracts and holds onto fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them more accessible to the digestive enzymes.

Once the stomach contents have been emulsified, fat-breaking enzymes work on the triglycerides and diglycerides to sever fatty acids from their glycerol backbones. As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucus that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal cells. Here, the fat components are released and disseminated into the cells of the digestive tract lining.

Just as lipids require special handling in the digestive tract to move within a water-based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triglycerides. Triglycerides, cholesterol, and phospholipids form lipoproteins when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triglycerides and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron, which is a large lipoprotein that now enters the lymphatic system and will soon be released into the bloodstream. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues.

Understanding Blood Cholesterol

You may have heard of the abbreviations LDL and HDL with respect to heart health. These abbreviations refer to low-density lipoprotein (LDL) and high-density lipoprotein (HDL), respectively. Lipoproteins are characterized by size, density, and composition. As the size of the lipoprotein increases, the density decreases. This means that HDL is smaller than LDL.

Major Lipoproteins

Chylomicrons . These lipoproteins are made in the small intestine cells after the digestion and absorption of fat from the foods that you eat. They primarily transport exogenous, or dietary, triglycerides from the gut to the cells of the body although they also carry dietary cholesterol and fat soluble vitamins. Chylomicrons are too large to be transported in the hepatic portal vein to the liver with the water soluble nutrients. Instead they enter the lymphatic system and are deposited directly into the bloodstream via the subclavian vein. They circulate throughout the body, delivering triglycerides to the body’s cells, especially adipose and muscle tissue, where the triglyceride can be used for energy or stored for later use. The remaining part of the chylomicron, or remnant, is delivered back to the liver for disposal.
Very low density lipoproteins (VLDLs) . Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport endogenous triglycerides from the liver to various tissues in the body. As the VLDLs travel through the circulatory system, the lipoprotein lipase strips the VLDL of triglycerides. As triglyceride removal persists, the VLDLs becomes smaller and more dense.
Low density lipoproteins (LDLs) . The remnants of VLDLs are converted to LDLs. LDLs are commonly known as the “bad cholesterol” and it is imperative that we understand their function in the body so as to make healthy dietary and lifestyle choices. LDLs carry cholesterol and other lipids from the liver to tissues throughout the body. LDLs are comprised of very small amounts of triglycerides, and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the LDLs deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with LDLs. Circulating LDLs in the bloodstream bind to these LDL receptors and are consumed. Once inside the cell, the LDL is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the LDLs. A deficiency of these LDL binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can build up in the arteries as oxidized plaques and lead to heart disease or atherosclerosis. Diets rich in saturated fats will inhibit the LDL receptors which are critical for regulating cholesterol levels.
High density lipoproteins (HDLs) . High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. This is also known as reverse cholesterol transport. HDLs have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Hence, these high-density lipoproteins are commonly called “good cholesterol.”

Blood Cholesterol Recommendations

For healthy total blood cholesterol, the desired range you would want to maintain is under 200 mg/dL. More specifically, when looking at individual lipid profiles, a low amount of LDL and a high amount of HDL prevents excess buildup of cholesterol in the arteries and wards off potential health hazards. An LDL level of less than 100 milligrams per deciliter is ideal while an LDL level above 160 mg/dL would be considered high. In contrast, a low value of HDL is a telltale sign that a person is living with major risks for disease. Values of less than 40 mg/dL for men and 50 mg/dL for women mark a risk factor for developing heart disease. In short, elevated LDL blood lipid profiles indicate an increased risk of heart attack, while elevated HDL blood lipid profiles indicate a reduced risk.

Current guidelines recommend testing for anyone over age twenty. If there is a family history of high cholesterol, your healthcare provider may suggest a test sooner than this. Testing calls for a blood sample to be drawn after nine to twelve hours of fasting for an accurate reading. (By this time, most of the fats ingested from the previous meal have circulated through the body and the concentration of lipoproteins in the blood will be stabilized.)

According to the National Institutes of Health (NIH), the following total cholesterol values are used to target treatment:

Desirable: Less than 200 mg/dL
Borderline high: 200–240 mg/dL
High risk: Greater than 240 mg/dL

According to the NIH, the following desired values are used to measure an overall lipid profile :

LDL: Less than 160 mg/dL (if you have heart disease or diabetes, less than 100 mg/dL)
HDL: Greater than 40–60 mg/dL
Triglycerides: 10–150 mg/dL

If your blood cholesterol numbers are not ideal, Figure 6.14 provides some lifestyle modifications that can help improve your cholesterol. For some people, especially if you have a family history of high cholesterol, medication will be required. Please consult with your doctor.

Figure 6.14 Improving Your Blood Cholesterol

Infographic summarizing dietary and exercise modifications to improve blood cholesterol levels.

Media Attributions

Lipid Digestion and Absorption © Allison Calabrese is licensed under a CC BY (Attribution) license
Blood Cholesterol © Natalie Fox is licensed under a CC BY (Attribution) license

6.3 Lipid Digestion, Absorption, and Transport Copyright © 2022 by Angela Harter Alger is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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5.4: Digestion And Absorption Of Lipids

Learning objectives.

Summarize the steps in lipid digestion and absorption.
Explain how lipids are used for energy and stored in the body.

Lipids are large molecules and generally are not water-soluble. Like carbohydrates and protein, lipids are broken into small components for absorption. Since most of our digestive enzymes are water-based, how does the body break down fat and make it available for the various functions it must perform in the human body?

From the Mouth to the Stomach

The first step in the digestion of triacylglycerols and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components.

Figure 5.4.1 : Lipid Digestion

In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides and fatty acids. The stomach’s churning and contractions help to disperse the fat molecules, while the diglycerides derived in this process act as further emulsifiers. However, even amid all of this activity, very little fat digestion occurs in the stomach.

Going to the Bloodstream

As stomach contents enter the small intestine, the digestive system sets out to manage a small hurdle, namely, to combine the separated fats with its own watery fluids. The solution to this hurdle is bile. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier. It attracts and holds on to fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them more accessible to the digestive enzymes.

Once the stomach contents have been emulsified, fat-breaking enzymes work on the triacylglycerols and diglycerides to sever fatty acids from their glycerol foundations. As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucous that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal microvillus. Here, the fat components are released and disseminated into the cells of the digestive tract lining.

Figure 5.4.2 : Fats can travel through the watery environment of the body due to the process of emulsion.

Just as lipids require special handling in the digestive tract to move within a water-based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triacylglycerols. Triacylglycerols, cholesterol, and phospholipids form lipoproteins when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triacylglycerols and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron, which is a large lipoprotein that now enters the lymphatic system and will soon be released into the bloodstream via the jugular vein in the neck. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues.

Cholesterols are poorly absorbed when compared to phospholipids and triacylglycerols. Cholesterol absorption is aided by an increase in dietary fat components and is hindered by high fiber content. This is the reason that a high intake of fiber is recommended to decrease blood cholesterol. Foods high in fiber such as fresh fruits, vegetables, and oats can bind bile salts and cholesterol, preventing their absorption and carrying them out of the colon.

If fats are not absorbed properly as is seen in some medical conditions, a person’s stool will contain high amounts of fat. If fat malabsorption persists the condition is known as steatorrhea. Steatorrhea can result from diseases that affect absorption, such as Crohn’s disease and cystic fibrosis.

The Truth about Storing and Using Body Fat

Before the prepackaged food industry, fitness centers, and weight-loss programs, our ancestors worked hard to even locate a meal. They made plans, not for losing those last ten pounds to fit into a bathing suit for vacation, but rather for finding food. Today, this is why we can go long periods without eating, whether we are sick with a vanished appetite, our physical activity level has increased, or there is simply no food available. Our bodies reserve fuel for a rainy day.

One way the body stores fat involves the body transforms carbohydrates into glycogen that is in turn stored in the muscles for energy. When the muscles reach their capacity for glycogen storage, the excess is returned to the liver, where it is converted into triacylglycerols and then stored as fat.

In a similar manner, much of the triacylglycerols the body receives from food is transported to fat storehouses within the body if not used for producing energy. The chylomicrons are responsible for shuttling the triacylglycerols to various locations such as the muscles, breasts, external layers under the skin, and internal fat layers of the abdomen, thighs, and buttocks where they are stored by the body in adipose tissue for future use. How is this accomplished? Recall that chylomicrons are large lipoproteins that contain a triacylglycerol and fatty-acid core. Capillary walls contain an enzyme called lipoprotein-lipase that dismantles the triacylglycerols in the lipoproteins into fatty acids and glycerol, thus enabling these to enter into the adipose cells. Once inside the adipose cells, the fatty acids and glycerol are reassembled into triacylglycerols and stored for later use. Muscle cells may also take up the fatty acids and use them for muscular work and generating energy. When a person’s energy requirements exceed the amount of available fuel presented from a recent meal or extended physical activity has exhausted glycogen energy reserves, fat reserves are retrieved for energy utilization.

As the body calls for additional energy, the adipose tissue responds by dismantling its triacylglycerols and dispensing glycerol and fatty acids directly into the blood. Upon receipt of these substances the energy-hungry cells break them down further into tiny fragments. These fragments go through a series of chemical reactions that yield energy, carbon dioxide, and water.

Key Takeaways

In the stomach fat is separated from other food substances. In the small intestines bile emulsifies fats while enzymes digest them. The intestinal cells absorb the fats.
Long-chain fatty acids form a large lipoprotein structure called a chylomicron that transports fats through the lymph system.
Chylomicrons are formed in the intestinal cells and carry lipids from the digestive tract into circulation.
Short- and medium-fatty chains can be absorbed directly into the bloodstream from the intestinal microvillus because they are water-soluble.
Cholesterol absorption is hindered by foods high in fiber.
When energy supplies are low the body utilizes its stored fat reserves for energy.

Discussion Starters

Explain the role of emulsifiers in fat digestion.
Name the part of the digestive system where most fat digestion and absorption occurs.
Describe the role of bile salts in the digestion of triacylglycerols and phospholipids.
Define chylomicron.
Explain how fiber-rich foods affect cholesterol absorption.
Discuss the body’s processes for using energy.
Digestion and Absorption of Lipids. Authored by : Medical LibreTexts Contributors. Provided by : LibreTexts. Located at : https://med.libretexts.org/Courses/Sacramento_City_College/SCC%3A_Nutri_300_(Coppola)/Chapters/05%3A_Lipids/5.4%3A_Digestion_and_Absorption_of_Lipids . License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

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Chapter 7: Lipids

7.6 Digestion and Absorption of Lipids

University of Hawai‘i at Mānoa Food Science and Human Nutrition Program

Lipids are large molecules and generally are not water-soluble. Like carbohydrates and protein, lipids are broken into small components for absorption . Since our digestive enzymes are secreted in a watery solution, how does the body break down fat and make it available for the various functions it must perform in the human body?

From the Mouth to the Stomach

The first step in the digestion of triglycerides and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase , along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components.

Bile in the Small Intestine

The majority of lipid digestion and absorption occurs in the small intestine. As stomach contents enter the small intestine, the digestive system must combine the separated fats with its own watery fluids. The solution to this hurdle is bile . Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier. It attracts and holds onto fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them much more accessible to the digestive enzymes.

Once the stomach contents have been emulsified, fat-breaking enzymes work on the triglycerides and diglycerides to sever fatty acids from their glycerol foundations. As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucus that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal microvillus. Here, the fat components are released and disseminated into the cells of the digestive tract lining.

Chylomicrons are too large to fit through the pores in capillaries, but they can fit through the larger openings in lacteals. Therefore, most dietary fat is absorbed into lacteals and circulates through the lymphatic system before being returned to the blood.

Cholesterols are poorly absorbed when compared to phospholipids and triglycerides. Cholesterol absorption is aided by an increase in dietary fat components and is hindered by high fiber content. This is the reason that a high intake of fiber is recommended to decrease blood cholesterol. Foods high in fiber such as fresh fruits, vegetables, and oats can bind bile salts and cholesterol, preventing their absorption and carrying them out of the colon.

The Truth about Storing and Using Body Fat

One way the body stores fat was previously touched upon in the Carbohydrates chapter. The body transforms carbohydrates into glycogen that is in turn stored in the muscles for energy. When the muscles reach their capacity for glycogen storage, the excess is returned to the liver, where it is converted into triglycerides and then stored as fat.

In a similar manner, much of the triglycerides the body receives from food is transported to fat storehouses within the body if not used for producing energy. The chylomicrons are responsible for shuttling the triglycerides to various locations such as the muscles, breasts, external layers under the skin, and internal fat layers of the abdomen, thighs, and buttocks where they are stored by the body in adipose tissue for future use. How is this accomplished? Recall that chylomicrons are large lipoproteins that contain a triglyceride and fatty-acid core. Capillary walls contain an enzyme called lipoprotein-lipase that dismantles the triglycerides in the lipoproteins into fatty acids and glycerol, thus enabling these to enter into the adipose cells. Once inside the adipose cells, the fatty acids and glycerol are reassembled into triglycerides and stored for later use. Muscle cells may also take up the fatty acids and use them for muscular work and generating energy. When a person’s energy requirements exceed the amount of available fuel presented from a recent meal or extended physical activity has exhausted glycogen energy reserves, fat reserves are retrieved for energy utilization.

As the body calls for additional energy, the adipose tissue responds by dismantling its triglycerides and dispensing glycerol and fatty acids directly into the blood. Upon receipt of these substances the energy-hungry cells break them down further into tiny fragments. These fragments go through a series of chemical reactions that yield energy, carbon dioxide, and water.

Understanding Blood Cholesterol

Major Lipoproteins

Recall that chylomicrons are transporters of fats throughout the watery environment within the body. After about ten hours of circulating throughout the body, chylomicrons gradually release their triglycerides until all that is left of their composition is cholesterol-rich remnants. These remnants are used as raw materials by the liver to formulate specific lipoproteins. Following is a list of the various lipoproteins and their functions:

VLDLs . Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport triglycerides from the liver to various tissues in the body. As the VLDLs travel through the circulatory system, the lipoprotein lipase strips the VLDL of triglycerides. As triglyceride removal persists, the VLDLs become intermediate-density lipoproteins.
IDLs . Intermediate-density lipoproteins transport a variety of fats and cholesterol in the bloodstream and are a little under half triglyceride in composition. While travelling in the bloodstream, cholesterol is gained from other lipoproteins while circulating enzymes strip its phospholipid component. When IDLs return to the liver, they are transformed into low-density lipoprotein.
LDLs . As low-density lipoproteins are commonly known as the “bad cholesterol” it is imperative that we understand their function in the body so as to make healthy dietary and lifestyle choices. LDLs carry cholesterol and other lipids from the liver to tissue throughout the body. LDLs are comprised of very small amounts of triglycerides, and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the LDLs deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with LDLs. Circulating LDLs in the bloodstream bind to these LDL receptors and are consumed. Once inside the cell, the LDL is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the LDLs. A deficiency of these LDL binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can lead to heart disease or atherosclerosis . Diets rich in saturated fats will prohibit the LDL receptors which, are critical for regulating cholesterol levels.
HDLs . High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. HDLs have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Hence, these high-density lipoproteins are commonly called “good cholesterol.”

Blood Cholesterol Recommendations

It is suggested that people consume omega-3 fatty acids such as alpha-linolenic acid in their diets regularly. Polyunsaturated fatty acids are especially beneficial to consume because they both lower LDL and elevate HDL, thus contributing to healthy blood cholesterol levels. The study also reveals that saturated and trans fatty acids serve as catalysts for the increase of LDL cholesterol. Additionally, trans fatty acids decrease HDL levels, which can impact negatively on total blood cholesterol.

Omega-3 fatty acids. University of Maryland Medical Center. http://www.umm.edu/altmed/articles/omega-3-000316.htm . Updated August 5, 2015. Accessed September 28, 2017. ↵

Absorption is the process of getting nutrients from the digestive tract into the blood or lymph.

Emulsifiers can keep oil and water mixed. Emulsions are mixtures of two liquids that do not mix.

Lingual lipase is a lipid-digesting enzyme in the mouth. It has a small role in digestion in adults, but may be important for infants to help break down triglycerides in breast milk.

Bile is produced in the liver and takes part in fat digestion. Bile acts as an emulsifier, or detergent. It, along with phospholipids, breaks the large triglyceride droplets into smaller triglyceride droplets that increase the surface area accessible for digestive enzymes.

Micelles are droplets with a fatty acid (hydrophobic) core and a water-soluble (hydrophilic) exterior. Bile salts in the digestive tract envelop fatty acids and monoglycerides to form micelles.

Chylomicrons are lipoproteins formed by the merging of a protein carrier, triglycerides, cholesterol, and phospholipids.

Atherosclerosis is a condition that occurs when too much plaque builds up in your arteries, causing them to narrow.

7.6 Digestion and Absorption of Lipids Copyright © by University of Hawai‘i at Mānoa Food Science and Human Nutrition Program is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Digestion and Absorption of Lipids

From the Mouth to the Stomach

Going to the Bloodstream

Just as lipids require special handling in the digestive tract to move within a water-based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triglycerides. Triglycerides, cholesterol, and phospholipids form lipoproteins when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triglycerides and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron, which is a large lipoprotein that now enters the lymphatic system and will soon be released into the bloodstream via the jugular vein in the neck. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues.

The Truth about Storing and Using Body Fat

Understanding Blood Cholesterol

Major Lipoproteins

VLDLs. Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport triglycerides from the liver to various tissues in the body. As the VLDLs travel through the circulatory system, the lipoprotein lipase strips the VLDL of triglycerides. As triglyceride removal persists, the VLDLs become intermediate-density lipoproteins.
IDLs. Intermediate-density lipoproteins transport a variety of fats and cholesterol in the bloodstream and are a little under half triglyceride in composition. While travelling in the bloodstream, cholesterol is gained from other lipoproteins while circulating enzymes strip its phospholipid component. When IDLs return to the liver, they are transformed into low-density lipoprotein.
LDLs. As low-density lipoproteins are commonly known as the “bad cholesterol” it is imperative that we understand their function in the body so as to make healthy dietary and lifestyle choices. LDLs carry cholesterol and other lipids from the liver to tissue throughout the body. LDLs are comprised of very small amounts of triglycerides, and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the LDLs deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with LDLs. Circulating LDLs in the bloodstream bind to these LDL receptors and are consumed. Once inside the cell, the LDL is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the LDLs. A deficiency of these LDL binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can lead to heart disease or atherosclerosis. Diets rich in saturated fats will prohibit the LDL receptors which, are critical for regulating cholesterol levels.
HDLs. High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. HDLs have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Hence, these high-density lipoproteins are commonly called “good cholesterol.”

Blood Cholesterol Recommendations

Chapter Attribution

Chapter 6.5 in Human Nutrition in a Canadian Context by Karine Hamm published by BCcampus in 2021 under a CC BY License.

Omega-3 fatty acids. University of Maryland Medical Center. http://www.umm.edu/altmed/articles/omega-3-000316.htm. Updated August 5, 2015. ↵

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4.4: Digestion and Absorption of Lipids

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Learning Objectives

Summarize the steps in lipid digestion and absorption.
Explain how lipids are used for energy and stored in the body.

From the Mouth to the Stomach

The first step in the digestion of triacylglycerols and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion and starts the breakdown of triacylglycerides. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components.

Going to the Bloodstream

As stomach contents enter the small intestine, the digestive system sets out to manage a small hurdle, namely, to combine the separated fats with its own watery fluids. The solution to this hurdle is bile. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier. It attracts and holds on to fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them more accessible to the digestive enzymes.

Once the stomach contents have been emulsified, fat-breaking enzymes work on the triacylglycerols and diglycerides to severe fatty acids from their glycerol foundations. As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucus that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal microvillus. Here, the fat components are released and disseminated into the cells of the digestive tract lining.

Just as lipids require special handling in the digestive tract to move within a water-based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triacylglycerols. Triacylglycerols, cholesterol, and phospholipids form lipoproteins when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triacylglycerols and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron, which is a large lipoprotein that now enters the lymphatic system, bypassing the liver, and will soon be released into the bloodstream via the jugular vein in the neck. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues. Entrance into the bloodstream can last up to 14 hours with the peak 30 to 3 hours post-meal.

Brief Overview of Triacylglyceride Metabolism

Fat cells are located in special depots in your body and there are many different locations, for example, abdominal (belly fat) or the hips. Also, a small amount of fat is stored in skeletal muscle too. See Figure 4.4.3 to see an adipocyte in skeletal muscle.

Once stored in the adipocyte (fat cell), the fat will remain there until it is needed to produce energy. Lipolysis is the process by which the triacylglyceride is removed from the lipid droplet with the fat cells, broken into 3 fatty acids and glycerol. The glycerol is secreted from the cells along with some but not all of the fatty acids. These are transported to the liver where the glycerol may be converted to glucose. The fatty acids may be converted to ketones or transported to other cells and burn to produce ATP.

The Truth about Storing and Using Body Fat

In a similar manner, much of the triacylglycerols the body receives from food is transported to fat storehouses within the body if not used for producing energy. The chylomicrons are responsible for shuttling the triacylglycerols to various locations such as the muscles, breasts, external layers under the skin, and internal fat layers of the abdomen, thighs, and buttocks where they are stored by the body in adipose tissue for future use. How is this accomplished? Recall that chylomicrons are large lipoproteins that contain a triacylglycerol and fatty-acid core. Capillary walls contain an enzyme called lipoprotein-lipase that dismantles the triacylglycerols in the lipoproteins into fatty acids and glycerol, thus enabling these to enter into the adipose cells. Once inside the adipose cells, the fatty acids and glycerol are reassembled into triacylglycerols and stored for later use. Muscle cells may also take up the fatty acids and use them for muscular work and for generating energy. When a person’s energy requirements exceed the amount of available fuel presented from a recent meal or extended physical activity has exhausted glycogen energy reserves, fat reserves are retrieved for energy utilization.

As the body calls for additional energy, the adipose tissue responds by dismantling its triacylglycerols and dispensing glycerol and fatty acids directly into the blood. Upon receipt of these substances, the energy-hungry cells break them down further into tiny fragments. These fragments go through a series of chemical reactions that yield energy, carbon dioxide, and water.

Key Takeaways

In the stomach fat is separated from other food substances. In the small intestines, bile emulsifies fats while enzymes digest them. The intestinal cells absorb the fats.
Long-chain fatty acids form a large lipoprotein structure called a chylomicron that transports fats through the lymph system.
Chylomicrons are formed in the intestinal cells and carry lipids from the digestive tract into circulation.
Short- and medium-fatty chains can be absorbed directly into the bloodstream via the portal system from the intestinal microvillus because they are water-soluble.
Cholesterol absorption is hindered by foods high in fiber.
When energy supplies are low the body utilizes its stored fat reserves for energy.

Discussion Starters

Explain the role of emulsifiers in fat digestion.
Name the part of the digestive system where most fat digestion and absorption occurs.
Describe the role of bile salts in the digestion of triacylglycerols and phospholipids.
Define chylomicron.
Explain how fiber-rich foods affect cholesterol absorption.
Discuss the body’s processes for using energy.

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Chapter 6. Lipids

Digestion and Absorption of Lipids

From the Mouth to the Stomach

Figure 6.10 Lipid Digestion and Absorption

Going to the Bloodstream

Figure 6.11 Micelle Formation

Figure 6.12 Schematic Diagram Of A Chylomicron

Just as lipids require special handling in the digestive tract to move within a water-based environment, they require similar handling to travel in the bloodstream. Inside the intestinal cells, the monoglycerides and fatty acids reassemble themselves into triglycerides. Triglycerides, cholesterol, and phospholipids form lipoproteins when joined with a protein carrier. Lipoproteins have an inner core that is primarily made up of triglycerides and cholesterol esters (a cholesterol ester is a cholesterol linked to a fatty acid). The outer envelope is made of phospholipids interspersed with proteins and cholesterol. Together they form a chylomicron, which is a large lipoprotein that now enters the lymphatic system and will soon be released into the bloodstream via the jugular vein in the neck. Chylomicrons transport food fats perfectly through the body’s water-based environment to specific destinations such as the liver and other body tissues.

Figure 6.13 Cholesterol and Soluble Fiber

The Truth about Storing and Using Body Fat

Figure 6.14 Storing and Using Fat

Understanding Blood Cholesterol

Major Lipoproteins

VLDLs. Very low-density lipoproteins are made in the liver from remnants of chylomicrons and transport triglycerides from the liver to various tissues in the body. As the VLDLs travel through the circulatory system, the lipoprotein lipase strips the VLDL of triglycerides. As triglyceride removal persists, the VLDLs become intermediate-density lipoproteins.
IDLs. Intermediate-density lipoproteins transport a variety of fats and cholesterol in the bloodstream and are a little under half triglyceride in composition. While travelling in the bloodstream, cholesterol is gained from other lipoproteins while circulating enzymes strip its phospholipid component. When IDLs return to the liver, they are transformed into low-density lipoprotein.
LDLs. As low-density lipoproteins are commonly known as the “bad cholesterol” it is imperative that we understand their function in the body so as to make healthy dietary and lifestyle choices. LDLs carry cholesterol and other lipids from the liver to tissue throughout the body. LDLs are comprised of very small amounts of triglycerides, and house over 50 percent cholesterol and cholesterol esters. How does the body receive the lipids contained therein? As the LDLs deliver cholesterol and other lipids to the cells, each cell’s surface has receptor systems specifically designed to bind with LDLs. Circulating LDLs in the bloodstream bind to these LDL receptors and are consumed. Once inside the cell, the LDL is taken apart and its cholesterol is released. In liver cells these receptor systems aid in controlling blood cholesterol levels as they bind the LDLs. A deficiency of these LDL binding mechanisms will leave a high quantity of cholesterol traveling in the bloodstream, which can lead to heart disease or atherosclerosis. Diets rich in saturated fats will prohibit the LDL receptors which, are critical for regulating cholesterol levels.
HDLs. High-density lipoproteins are responsible for carrying cholesterol out of the bloodstream and into the liver, where it is either reused or removed from the body with bile. HDLs have a very large protein composition coupled with low cholesterol content (20 to 30 percent) compared to the other lipoproteins. Hence, these high-density lipoproteins are commonly called “good cholesterol.”

Figure 6.15 Lipoprotein Classes

The classification of the major types of lipoproteins are based on their densities. Density range is shown as well as lipid (red) and protein (blue) content. ( Diagram not to scale) / CC BY 3.0

Blood Cholesterol Recommendations

Omega-3 fatty acids. University of Maryland Medical Center. http://www.umm.edu/altmed/articles/omega-3-000316.htm. Updated August 5, 2015. Accessed September 28, 2017. ↵

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Digestion and absorption of lipids

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Digestion and Absorption of Lipids
The products of fat digestion diffuse across the membrane of the intestinal cells, and bile salts are recycled back to do more work emulsifying fat and forming micelles. Figure 5.22. Lipid digestion and absorption in the small intestine. Once inside the intestinal cell, short- and medium-chain fatty acids and glycerol can be directly absorbed ...
5.4: Digestion and Absorption of Lipids
These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components. Figure 5.4.1 5.4. 1: Lipid Digestion. In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids.
5.6: Digestion and Absorption of Lipids
From the Mouth to the Stomach. The first step in the digestion of triglycerides and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an ...
Intestinal lipid absorption
Digestion and absorption of TAGs. TAG is digested primarily by pancreatic lipase in the upper segment of the jejunum. This process generates a liquid-crystalline interface at the surface of the emulsion particles (13, 161).The activity of pancreatic lipase on the sn-1 and sn-3 positions of the TAG molecule results in the release of 2-monoacylglycerol (2-MAG) and free fatty acids (FFAs) (122 ...
Digestion and absorption of lipids
Abstract: Digestion and absorption of dietary lipids is a very complex multi-step process, starting in the stomach, and ending in the small intestine. Physicochemical remodelling and lipase-catalysed hydrolysis are key events enabling efficient lipid assimilation. It results in transient marked postprandial changes in plasma lipoprotein ...
Intestinal lipid absorption
Digestion and absorption of TAGs. TAG is digested primarily by pancreatic lipase in the upper segment of the jejunum. This process generates a liquid-crystalline interface at the surface of the emulsion particles (13, 161).The activity of pancreatic lipase on the sn-1 and sn-3 positions of the TAG molecule results in the release of 2-monoacylglycerol (2-MAG) and free fatty acids (FFAs) (122 ...
Digestion and Absorption of Lipids
From the Mouth to the Stomach. The first step in the digestion of triglycerides and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an ...
Digestion and Absorption of Lipids
An adult person should consume around 60-90 g of fats per day. Intake of calories from saturated fatty acids and trans fatty acids should be <10% and 2% of total calories, respectively, per day. Lipids are important source of energy for living organisms. A healthy adult person requires around 2800 calories per day.
5.6: Digestion and Absorption of Lipids
The enzyme lingual lipase, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components. Figure \(\PageIndex{1}\): Lipid Digestion and Absorption.
5.5 Digestion and Absorption of Lipids
The digestive process has to break those large droplets of fat into smaller droplets and then enzymatically digest lipid molecules using enzymes called lipases. The mouth and stomach play a small role in this process, but most enzymatic digestion of lipids happens in the small intestine. From there, the products of lipid digestion are absorbed ...
Digestion and absorption of lipids
Abstract: Digestion and absorption of dietary lipids is a very complex multi-step process, starting in the stomach, and ending in the small intestine. Physicochemical remodelling and lipase-catalysed hydrolysis are key events enabling efficient lipid assimilation. It results in transient marked postprandial changes in plasma lipoprotein ...
6.3 Lipid Digestion, Absorption, and Transport
However, lipid digestion is more complicated than carbohydrate digestion because most of our digestive tract and digestive enzymes are water based. Figure 6.13 shows a general overview of what happens to lipids at each part of the digestive tract. Each step is described in more detail below. Figure 6.13 Overview of Lipid Digestion, Absorption ...
5.4: Digestion And Absorption Of Lipids
Figure 5.4.1: Lipid Digestion. In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides and fatty acids. The stomach's churning and contractions help to disperse the fat ...
Digestion and Absorption of Lipids
Figure 5.11 Lipid Digestion and Absorption. In the stomach, gastric lipase starts to break down triglycerides into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triglycerides are converted to diglycerides and fatty acids.
5.2: Digestion and Absorption of Lipids
Figure 5.2.1 5.2. 1: Lipid Digestion ( CC BY-NC-SA 4.0 ; LibreTexts An Introduction to Nutrition (Zimmerman)) In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids (Figure 5.2.1 5.2. 1 ). Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to ...
7.6 Digestion and Absorption of Lipids
The majority of lipid digestion and absorption occurs in the small intestine. As stomach contents enter the small intestine, the digestive system must combine the separated fats with its own watery fluids. The solution to this hurdle is bile. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier ...
5.4: Digestion and Absorption of Lipids
As a result, the fats become tiny droplets and separate from the watery components. Figure 5.4.1 5.4. 1: Lipid Digestion. In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides ...
5.3: Digestion and Absorption of Lipids
Discuss the body's processes for using energy. 5.3: Digestion and Absorption of Lipids is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts. Lipids are large molecules and generally are not water-soluble. Like carbohydrates and protein, lipids are broken into small components for absorption.
Digestion and Absorption of Lipids
The enzyme lingual lipase, along with a small amount of phospholipid as an emulsifier, initiates the process of digestion. These actions cause the fats to become more accessible to the digestive enzymes. As a result, the fats become tiny droplets and separate from the watery components. Lipid Digestion and Absorption by Calabrese, A., via CC BY 4.0
4.4: Digestion and Absorption of Lipids
Figure 4.4.1 4.4. 1: Lipid Digestion. In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides and fatty acids.
Digestion and Absorption of Lipids
From the Mouth to the Stomach. The first step in the digestion of triglycerides and phospholipids begins in the mouth as lipids encounter saliva. Next, the physical action of chewing coupled with the action of emulsifiers enables the digestive enzymes to do their tasks. The enzyme lingual lipase, along with a small amount of phospholipid as an ...

Digestion and Absorption of Lipids

1. Lipid Digestion in the Mouth

2. Lipid Digestion in the Stomach

3. Lipid Digestion in the Small Intestine

4. Lipid Absorption from the Small Intestine

Special Adaptations for Lipid Digestion in Infants

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5.5 Digestion and Absorption of Lipids

1. Lipid Digestion in the Mouth

2. Lipid Digestion in the Stomach

3. Lipid Digestion in the Small Intestine

4. Lipid Absorption from the Small Intestine

Special Adaptations for Lipid Digestion in Infants

Review Questions

References:

Image Credits:

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6.3 Lipid Digestion, Absorption, and Transport

From the Mouth to the Stomach

Entering the Bloodstream

Understanding Blood Cholesterol

Major Lipoproteins

Blood Cholesterol Recommendations

Media Attributions

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5.4: Digestion And Absorption Of Lipids

From the Mouth to the Stomach

Going to the Bloodstream

The Truth about Storing and Using Body Fat

Key Takeaways

Discussion Starters

7.6 Digestion and Absorption of Lipids

From the Mouth to the Stomach

Bile in the Small Intestine

The Truth about Storing and Using Body Fat

Understanding Blood Cholesterol

Major Lipoproteins

Blood Cholesterol Recommendations

Digestion and Absorption of Lipids

From the Mouth to the Stomach

Going to the Bloodstream

The Truth about Storing and Using Body Fat

Understanding Blood Cholesterol

Major Lipoproteins

Blood Cholesterol Recommendations

Chapter Attribution

Share This Book

4.4: Digestion and Absorption of Lipids

From the Mouth to the Stomach

Going to the Bloodstream

Brief Overview of Triacylglyceride Metabolism

The Truth about Storing and Using Body Fat

Key Takeaways

Discussion Starters

Digestion and Absorption of Lipids

From the Mouth to the Stomach

Going to the Bloodstream

The Truth about Storing and Using Body Fat

Understanding Blood Cholesterol

Major Lipoproteins

Blood Cholesterol Recommendations

Share This Book

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VIDEO

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