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Jamie Pope, Steven Nizielski, and Alison McCook

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1 Jamie Pope, Steven Nizielski, and Alison McCook
NUTRITION for a Changing World FIRST EDITION Chapter 6 The Lipids The Skinny on Fat My class period is 1 hour and 40 minutes. If your class period is shorter, you may wish to divide these 60 slides. I suggest a break after slide 41. © 2016 by W. H. Freeman and Company & Scientific American

2 Chapter 6 Objectives Identify the four major categories of dietary lipids Describe the structural differences between saturated, monounsaturated, and polyunsaturated fats Identify the types of foods that are rich in monounsaturated fat, polyunsaturated fat, and saturated fat Identify dietary sources of cholesterol Name two roles of phospholipids in the body Describe the process of lipid digestion and explain how emulsification assists in the process List the four major lipoproteins and describe their functions in the transport of lipids Identify the two essential fatty acids, their primary structural difference, and food sources of each in the diet  Describe how to use a Nutrition Facts Panel to evaluate a food’s fat content

3 All contain the same calories
Which of these sources of dietary fat contain the fewest calories per tablespoon? Butter Canola oil Coconut oil Margarine (stick) Margarine spread) Olive oil All contain the same calories I use the next few polling slides as an adaption of the chapter’s Bring It Home to open the class. They illustrate several misconceptions before the lecture begins. Students say that olive oil has the fewest calories! I hand out packages, containers, or bottles of each of the listed fats to students and have them share. I’ll say, “Okay, butter, how may calories per tablespoon?” and so on.

4 Which of these sources of dietary fat is most saturated?
Butter Canola oil Coconut oil Margarine (stick) Margarine (spread) Olive oil All the same They never guess coconut oil! Before class that is….

5 Which of these dietary fat sources contains the most monounsaturated fat?
Butter Canola oil Coconut oil Margarine (stick) Margarine (spread) Olive oil All the same Students usually get this one correct.

6 Which of these sources of dietary fat contain the most trans fatty acids?
Butter Canola oil Coconut oil Margarine (stick) Margarine (spread) Olive oil All the same Many say butter has the most trans fat, so this is a good opportunity to introduce different types of fatty acids. The correct answer is margarine stick (if you use a package, I suggest a generic brand that contains trans fat for illustration).

7 Which of these sources of dietary fat contain cholesterol?
Butter Canola oil Coconut oil Margarine (stick) Margarine (spread) Olive oil They all contain cholesterol. Most students choose #7 (that they all contain cholesterol), but the correct answer, of course, is butter.

8 Image from Bring It Home activity

9 The relationship between dietary fats and heart disease is complicated…
How did native Greenlanders with a diet high in fat show the world that not all lipids are created equal? In 1970 a young doctor, Jorn Dyerberg, visited native Greenlanders, known as the Inuit. Living in one of the coldest places on Earth, the Inuit eat a high-fat diet rich in seal blubber and fatty fish; yet unlike people in Denmark and the United States, they have much less heart disease. He found that even though their diet’s were high in fat, they did not have a corresponding high blood cholesterol. So, we know that different lipids affect health differently.

10 Lipids include fatty acids, triglycerides, sterols, and phospholipids.
Structurally diverse group of molecules Contain carbon, hydrogen, and oxygen Generally insoluble in water (don’t dissolve in water)

11 Lipids have important functions in the body.
Component of cell membranes Give cell membranes flexibility and integrity Fats supply a concentrated source of energy and fat-soluble nutrients 9 calories per gram Essential fatty acids (linoleic acid and alpha-linolenic acid) Fat-soluble vitamins A, D, E, and K Facilitate the transport of nutrients Enhance the absorption of fat-soluble vitamins

12 Lipids have important roles in the body and in food.
It is the primary source of the body’s energy reserves (stored in adipose tissue). The adipose tissue cushions, protects, and insulates the body’s organs. Fats contribute to the sensation of feeling full Fats stay in the stomach longer. Fats are absorbed over a longer period of time. Fats increase the flavor and palatability of foods. Fats contribute to the texture and aroma of foods.

13 The four primary classes of lipids are diverse in structure and function.

14 Fatty acids are the primary components of triglycerides and phospholipids.
Consist of a chain of carbon atoms with hydrogen atoms attached to each carbon Differ in chain length and saturation Determines their function and role in health and disease Saturation = how many hydrogen atoms fill the available carbon bonds Fatty acids differ in length, and so they are categorized by the length of their hydro-carbon chains, as well as in their degree of saturation (how many hydrogen atoms fill the available bonds with carbon). Short-chain fatty acids have fewer than six carbons; medium-chain fatty acids have 6 to 12 carbons, and long-chain fatty acids have more than 12 carbons. Both properties (degree of saturation and chain length) determine their function in the body and role in health and disease.

15

16 Fatty acids differ in their degree of saturation.
Saturated fatty acids Fully hydrogenated All carbons “saturated” with hydrogen No double bonds Food sources Tend to be solid at room temperature Animal origin Tropical oils Hydrogenated atoms fill every possible bond of the carbon atoms. See how they stack tightly and lay compactly. This makes them more solid. Food sources include animal fats since animals can make saturated fatty acids. Such food sources include pork, beef, chicken, egg yolk, milk, dairy, lard, and beef tallow. Some vegetable sources are also highly saturated. If you have ever seen palm or coconut oil in the bottle, you will notice they are also solid at room temperature. Saturated fatty acids are thought to raise blood cholesterol, which we will discuss more in the next chapter on heart disease.

17 Fatty acids differ in their degree of saturation.
Unsaturated fatty acids Fewer hydrogen atoms Contain one or more double bonds Tend to be liquid at room temperature You can see that monounsaturated fatty acids are missing some hydrogens, causing a kink in the straight fatty acid chain and not allowing the fatty acids to stack tightly. This allows for the fat to be more liquid at room temperature than a more saturated fat. Monounsaturated fatty acids are rich in olives, olive and canola oils, and avocados, as well as many nuts, like almonds and peanuts. These fatty acids raise blood cholesterol less. We will talk more about them when we discuss heart disease in the next chapter.

18 Unsaturated fats differ in the number of double bonds present.
Monounsaturated fatty acids One double bond or point of unsaturation Food sources Olives, avocados, and some nuts, like peanuts and almonds You can see that monounsaturated fatty acids are missing some hydrogens, causing a kink in the straight fatty acid chain and not allowing the fatty acids to stack tightly. This allows for the fat to be more liquid at room temperature than a more saturated fat. Monounsaturated fatty acids are rich in olives, olive and canola oils, and avocados, as well as many nuts, like almonds and peanuts. These fatty acids raise blood cholesterol less. We will talk more about them when we discuss heart disease in the next chapter.

19 Unsaturated fats differ in the number of double bonds present.
Polyunsaturated fatty acids More than one point of unsaturation or more than one double bond Food sources Most vegetable oils As you can see, there are many bends in polyunsaturated fatty acids and the structures do not pack tightly; therefore, these fats are usually very liquid at room temperature. Unfortunately because of the many double bonds, they are also less stable and more prone to rancidity and spoiling compared to other fats. Polyunsaturated fatty acids are rich in vegetables oils such as sesame, sunflower, soy, and corn oils. These fatty acids don’t raise blood cholesterol but tend to become rancid, or spoil, the fastest since the double bonds make them less stable to free radicals or oxidation.

20 Food sources of fatty acids are blends of saturated and unsaturated fats. No fat or oil is completely saturated or unsaturated. Point out examples.

21 Saturated Fats Are found only in foods of animal origin
Increase risk of heart disease significantly more than trans fats Include no more than one double bond Are usually solid at room temperature Review question. Correct answer is D.

22 Triglycerides are commonly called “fats.”
Three-carbon glycerol molecule with three fatty acids attached Make up 95% of lipids in our food and 99% of the stored fat in our bodies The types of fatty acids that attach to triglycerides give them their characteristics in food. If they are mostly saturated, then they will be a solid fat at room temperature, such as butter. If they are mostly unsaturated, they will be liquid, like vegetable oils. Since triglycerides have three fatty acids attached to each glycerol molecule, they will have a mixture of saturated and unsaturated fatty acids, but the majority will give the fat its properties. Triglycerides are a primary form of lipid in food and a primary form of fat stored in the body.

23 Sterols are complex lipids.
Sterols have four interconnected carbon rings, with an oxygen and a hydrocarbon side chain. Cholesterol is a sterol produced by the liver. The most common sterol is cholesterol. It is a component of cell membranes and a precursor for the synthesis of bile acids, vitamin D, and steroid hormones, such as estrogen and testosterone.

24 Cholesterol is only found in animal foods.
The presence of cholesterol in cell membranes is a distinguishing characteristic between plant and animal cells. Cholesterol is only found in animal foods. It is not an essential nutrient as the liver produces sufficient amounts to meet the body’s needs. Cholesterol is synthesized in nearly every tissue in the body, but in particularly large quantities by the liver. Approximately 75% of the cholesterol in blood is made in our body, which provides all the cholesterol needed for body functions. Although a dietary source of cholesterol is not required, we consume cholesterol in animal foods, such as meats and dairy products. Indeed, the presence of cholesterol in cell membranes is one distinguishing characteristic between plant and animal cells, thus dietary cholesterol is found only in foods of animal origin. Plants synthesize other types of sterols (and the closely related stanols), but these types are poorly absorbed by the body and can actually interfere with and lower cholesterol absorption. For this reason, some spreads and other food products are fortified with plant sterols or stanols to help lower cholesterol levels in the body. Chapter 7 further explores the relationship of cholesterol and other dietary fats on blood cholesterol.

25 Cholesterol has varied functions in the body.
Critical component of cell membranes Not present in cell membranes of plants Precursor for the synthesis of bile acids, vitamin D, and steroid hormones Does not provide calories

26 Cholesterol Is found in all hydrogenated fats
Is found in every cell of our bodies Contains 9 calories per gram Is supplied primarily through our diets Review question. Correct answer is B.

27 Phospholipids can be produced by the body.
Three-carbon glycerol molecule with two fatty acids and a phosphate group on the third carbon Unlike other lipids, the unique structural arrangement allows phospholipids to suspend fat in water Explain the properties of phospholipids and how the phosphate group is water soluble, giving it a “head group” that likes water and the fatty acid tail that attracts lipids, allowing for its unique function in cell membranes and lipoproteins.

28 Phospholipids have varied roles in the body and in food.
Primary component of cell membranes Component of lipoproteins that transport lipids in the blood Lecithin is a phospholipid found in the body as well as in food products Can be found in egg yolks, liver, and some plant foods Not an essential nutrient Functions as an emulsifier which keeps water and lipids from separating Explain the properties of phospholipids and how the phosphate group is water soluble, giving it a “head group” that likes water and the fatty acid tail that attracts lipids, allowing for its unique function in cell membranes and lipoproteins.

29 Most lipid digestion occurs in the small intestine.
Limited amount of lipid digestion in mouth and stomach by lipases Digestion in small intestine facilitated by: Bile acids Emulsification Lipases Little digestion of lipids occurs in the mouth and stomach; most occurs in the small intestine. There is some lingual lipase added to food in the mouth and some gastric lipase in gastric juices added to food in the stomach, starting lipid digestion. If we bypass the mouth and stomach, we can still digest and absorb fat, as there is lipase in the intestine from the pancreas as well. In the small intestine, we are able to add bile that was produced in the liver from cholesterol and heme and stored in the gall bladder to be released when signaled. This then mixes with lipids in the small intestine and emulsifies. Now it is mixed and can be acted on by lipase released with other digestive enzymes from the pancreas into the small intestine.

30 The process of emulsification aids digestion by allowing fats to mix with water.
Bile acids make emulsification possible. Emulsified lipids facilitate action of lipases. Fats cannot mix with water because lipids are not water soluble; the fat tends to clump together in the intestine’s watery environment. The body’s solution to that problem is emulsification. Emulsification aids digestion by breaking up large fat globules into smaller droplets so that fat-digesting enzymes can operate efficiently. Bile acids produced in the liver make emulsification possible. Bile acids have a water-soluble and fat-soluble “face.” These two-faced molecules attach to lipids, so that the lipids remain suspended in water instead of clumping together.

31 Lipids are not soluble in water and thus require a carrier for transport.
[Insert infographic 6.6 ] Dietary lipids incorporated into transport particles for absorption Absorbed initially into lymphatic system which delivers to bloodstream Bile is made in the liver from cholesterol and heme and then stored in the gallbladder to be released when stimulated by food entering. The bile coats the lipid, emulsifying it and allowing it to mix and be acted on by pancreatic lipase. Once the fatty acids are cleaved from the glycerol molecule by lipase, the enzyme that digests triglyceride, they can be absorbed into the enterocytes, cells of the intestine.

32 Bile is made in the liver from cholesterol and heme and then stored in the gallbladder to be released when stimulated by food entering. The bile coats the lipid, emulsifying it and allowing it to mix and be acted on by pancreatic lipase. Once the fatty acids are cleaved from the glycerol molecule by lipase, the enzyme that digests triglyceride, they can be absorbed into the enterocytes, cells of the intestine.

33 Bile is made in the liver from cholesterol and heme and then stored in the gallbladder to be released when stimulated by food entering. The bile coats the lipid, emulsifying it and allowing it to mix and be acted on by pancreatic lipase. Once the fatty acids are cleaved from the glycerol molecule by lipase, the enzyme that digests triglyceride, they can be absorbed into the enterocytes, cells of the intestine.

34 Lipids do not travel freely in the blood.
Lipoproteins are the primary carriers. Lipids are not water soluble, so they will separate out if put directly into the blood. Therefore they must be packaged into “trucks” to transport or carry them around to the tissues. These trucks are called lipoproteins. Proteins and phospholipids are on the outside, and triglycerides and sterols are inside.

35 Lipoproteins are classified by their density and function.
Chylomicrons Very low–density lipoproteins (VLDLs) Low-density lipoproteins (LDLs) High-density lipoproteins (HDLs) Lipids are not water soluble, so they will separate out if put directly into the blood. Therefore they must be packaged into “trucks” to transport or carry them around to the tissues. These trucks are called lipoproteins. Proteins and phospholipids are on the outside, and triglycerides and sterols are inside.

36 Lipoproteins circulate lipids throughout the body.

37 Chylomicrons are the primary carrier of lipids in our diet.
Large lipoproteins made in intestinal cells Transport primarily triglycerides from the small intestine to adipose tissue, cardiac muscle and skeletal muscle via the lymph to the bloodstream The primary lipids in our diets are triglyceride chylomicrons. They primarily transport triglycerides into the body to tissues to use for energy and storage. Fat is very light; hence it floats in water. Chylomicrons are the least-dense lipoproteins, as they contain mostly fats/triglycerides.

38 Very low-density lipoproteins transport primarily triglycerides.
Very low–density lipoprotein (VLDL) Made in the liver Primary carrier of triglycerides from liver to muscle and adipose tissue Very low-density lipoproteins are made in the liver. The liver takes up chylomicron remnants which can be repackage into VLDL along with triglycerides made in the liver from energy. Very low-density lipoproteins transport triglycerides/fat made in the body to cells for storage and energy.

39 Low-density lipoprotein (LDL)
Low-density lipoproteins are the primary carrier of cholesterol to all cells. Low-density lipoprotein (LDL) Made in the liver Transports cholesterol from the liver to the cells of the body Elevated levels associated with increased risk of heart disease Often called “bad cholesterol” Low-density lipoproteins (LDL) are made in the liver. The liver makes cholesterol and triglycerides. Repackage very low-density lipoproteins. Low-density lipoproteins are the primary transporters of cholesterol to the cells that need cholesterol. They are commonly referred to as blood cholesterol. Cholesterol is very important; it is part of all cell membranes and the precursor to many hormones in the body. We can make all the cholesterol our body needs in our liver, so it is not essential to consume cholesterol in our diets. Too much cholesterol is associated with an increased risk of heart disease, as LDL is believed to deliver excess cholesterol into the arteries, causing increased blockage when elevated, which we will talk more about in the next chapter. But for this reason LDL cholesterol is sometimes called the “lousy” or bad cholesterol. A diet high in saturated fat and total fat is thought to raise a person’s LDL cholesterol.

40 High-density lipoproteins carry cholesterol from cells and tissues back to liver.
High-density lipoprotein (HDL) Contain higher proportion of protein “Reverse cholesterol transporter” High levels of HDL associated with lower heart disease risk Often called “good cholesterol” High-density lipoprotein (HDL) is made primarily in the liver; phospholipid and apoprotein A together form HDL. They are mostly made of protein and phospholipid. Since this lipoprotein is high in protein and phospholipids and low in actual lipids, it attracts cholesterol and triglycerides that cells don’t need and carries them back to the liver to be repackaged or made into bile, which can be excreted into the intestine. Since it helps to carry cholesterol out of areas with too much cholesterol, it is thought to help unclog arteries and reduce the risk of heart disease. This has led to it’s nickname as the “healthy” or good cholesterol. An increase in this blood cholesterol is associated with a reduced risk of heart disease. So, a blood lipid panel showing high LDL and low HDL is considered a risk factor for heart disease.

41 The concentrations of total cholesterol, HDL, LDL , and triglycerides in the blood affect risk of cardiovascular disease. From Chapter 7: I include this slide from Chapter 7 to illustrate the link with cardiovascular disease. If not teaching Chapter 7 (lipids and heart disease) specifically in your course (I don’t in my intro course but rather in another application course), then I suggest pulling in a few select slides from Chapter 7. I also include info on the Mediterranean diet from Chapter 9 with my chapter slides since, as with Chapter 7, I cover plant-based diets in the application course.

42 Essential fatty acids must be supplied through the diet.
The body cannot synthesize: Omega-6 fatty acids Linoleic acid Omega-3 fatty acids Linolenic acid Although our body can make many lipids, including cholesterol, saturated fat, and omega-9 fatty acids, it cannot make unsaturated fatty acids with the first double bond from the methyl end at the third or sixth carbon (omega-3 or omega-6 fatty acids). Therefore, linoleic acid and linolenic acid are fatty acids that our bodies cannot make, and they are required in our diet.

43 Linoleic acid is the most abundant polyunsaturated fat in the diet.
Omega-6 fatty acids—linoleic acid An essential fatty acid required for varied functions including: Growth Synthesis of hormone-like compounds (eicosanoids) Primary sources are cooking oils, salad dressings, nuts and seeds

44 Linolenic acid intake is low in the American diet.
Omega-3 fatty acids—(alpha)linolenic acid An essential fatty acid required for: Structural component of cell membranes Synthesis of hormone-like compounds (eicosanoids) EPA (Eicosaptenoic acid) DHA (docosahenxenoic acid) EPA and DHA are slowly produced from linolenic acid. Precursor for compounds that regulate blood pressure and clotting Found in walnuts, flaxseed, canola oil, soybeans, chia seeds Best sources are marine oils (cold water fish) due to content of DHA and EPA

45 Getting a proper balance of omega-6 and omega-3 fatty acids is important.
Americans consume a disportionate amount of linoleic acid (omega-6 fatty acids) in comparison to linolenic acid (omega-3 fatty acids) Omega-3 fatty acids are associated with decreased risk of heart disease and improved brain function. The U.S. diet is low in omega-3 fatty acids. The Inuits, with their high intake of fish, have high levels of EPA and DHA, which helps protect them against heart disease. Research has shown that eating the right amount of omega-3 fatty acids may reduce blood clotting, inflammation, and blood pressure and help eyesight and cognition. This helps explain why too much fat is never a good thing but too little of specific types of fats can be bad for our health, too. Our findings from the research in Greenland show the benefits of omega-3 fatty acids.

46 The U. S. diet is low in omega-3 fatty acids
The U.S. diet is low in omega-3 fatty acids. The Inuits, with their high intake of fish, have high levels of EPA and DHA, which helps protect them against heart disease. Research has shown that eating the right amount of omega-3 fatty acids may reduce blood clotting, inflammation, and blood pressure and help eyesight and cognition. This helps explain why too much fat is never a good thing but too little of specific types of fats can be bad for our health, too. Our findings from the research in Greenland show the benefits of omega-3 fatty acids.

47 How often do you eat fish?
Never Once a month Once a week Two or more times per week

48 DHA and EPA are omega-3 fatty acids found naturally in fish oils.
Highly unsaturated with 4 to 6 double bonds Fluid at cold temperatures DHA = docosahexanoic acid EPA = eicosapentaenoic acid Can also be produced from ALA (alpha-linolenic acid) Keep membranes and fat in fish flexible in cold water DHA and EPA form biologically active compounds to reduce blood pressure and tendency of blood to clot American Heart Association recommends 2 servings a week of omega-3 rich fish Unclear if fish oil supplementation has same benefit

49 Partial hydrogenation creates trans fatty acids
Much of the fat we consume has been hydrogenated, making unsaturated fat more solid and stable. Hydrogenation Adding hydrogen to an unsaturated fat makes it saturated (full of hydrogen) Can improve taste and texture Partial hydrogenation creates trans fatty acids Adding hydrogen to an unsaturated fat can alter the position of the double bonds Altering from natural “cis” to a “trans” chemical configuration No one likes to put liquid on their toast because it makes it soggy. Liquid oils, because they are unsaturated, are less stable and go rancid more quickly. Therefore, industry often hydrogenates oil to make it more stable and more solid; think of vegetable oil made into margarine or shortening, for example. However, this process repositions the hydrogens into new bonds, some of which will be trans double bonds. This creates trans fats, which are double bonds with hydrogens on opposite sides. With trans fats there is an increased risk of raising blood LDL cholesterol levels. Research shows that trans fats behave like saturated fats in the body and raise LDL cholesterol, increasing a person’s risk for heart disease.

50 Trans fatty acids increase risk of heart disease more than any other type of fat.
Raise “bad” cholesterol and lower “good” cholesterol No one likes to put liquid on their toast because it makes it soggy. Liquid oils, because they are unsaturated, are less stable and go rancid more quickly. Therefore, industry often hydrogenates oil to make it more stable and more solid; think of vegetable oil made into margarine or shortening, for example. However, this process repositions the hydrogens into new bonds, some of which will be trans double bonds. This creates trans fats, which are double bonds with hydrogens on opposite sides. With trans fats there is an increased risk of raising blood LDL cholesterol levels. Research shows that trans fats behave like saturated fats in the body and raise LDL cholesterol, increasing a person’s risk for heart disease.

51 The FDA has proposed a ban on the addition of trans fats to food products.
In 2006, mandatory part of Nutrition Facts Panel Products labeled “trans fat-free” must contain less than 0.5 grams As little as 1% of total calories from trans fat can increase risk of heart disease and stroke. Small amounts found naturally in full-fat dairy and beef Most comes from partially hydrogenated oils Found in commercial baked goods, packaged snacks, margarines, frozen pizzas, and fried potatoes As little as 1% or approximately 2.2 grams of total calories from trans fats can increase the risk of heart disease, stroke, and sudden death from these and other causes.

52 Current Fat Intake and Recommendations
Institutes of Medicine recommends AMDR total fat between 20% to 35% of total calories Most fat should come from unsaturated sources Eat as little saturated fat (<10%), trans fat, and cholesterol as possible Substitute healthier fats for unhealthy fats Caution substituting fat with simple or refined carbohydrates

53 Fat substitutes imitate the taste, texture, and cooking properties of fat.
Fewer calories Potential side effects Olestra (Olean) Cannot be digested or absorbed FDA mandates warning Many products are used as fat substitutes, such as gums and pectins, in fat-free products. These are all considered safe and present in other foods. Olean, or Olestra, is a sugar molecule with fatty acids attached, which the body cannot digest or absorb. Therefore it passes straight through the GI tract without being absorbed. This allows Olean to give the properties to food for taste and texture without adding fat to the body. However, it can also decrease the absorption of fat-soluble vitamins since they tend to stay near fat molecules. The FDA requires labeling to include: “Olestra may cause abdominal cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients.”

54 How do we determine the amounts and types of fats in the foods we eat
How do we determine the amounts and types of fats in the foods we eat? Read food labels.

55 Current Fat Intake and Recommendations

56

57 2015 Dietary Guidelines for Americans
DGAs recommend limiting saturated fat to < 10% of total calories. Strictly limit intake of trans fatty acids. In contrast to earlier editions, the 2015 guidelines do not establish specific limits for dietary cholesterol, but qualify that eating as little of it as possible is advisable within a healthy eating pattern.

58 Summary Lipids are composed of carbon, hydrogen, and a small amount of oxygen, and they are insoluble in water. Lipids are diverse in structure and function. Lipids serve many critical functions in the body. The four classes of lipids are fatty acids, triglycerides, phospholipids, and sterols. Fatty acids are the primary components of triglycerides and phospholipids. Fatty acids are either saturated or unsaturated, depending upon the number of hydrogen atoms filling their carbon bonds.

59 Summary (cont’d) Saturated fatty acids are fully hydrogenated and found in animal foods and tropical oils. Monounsaturated fatty acids have one double bond and are rich in foods like olives, nuts, and avocados. Polyunsaturated fats contain more than one double bond and are rich in most vegetable oils. Triglycerides are the primary source of lipid in our diet, the storage form of lipid in our body, and provide a concentrated energy source and essential fatty acids. Essential fatty acids include linoleic (an omega-6 fatty acid) and linolenic (an omega-3 fatty acid) acids, which are required for the synthesis and production of eicosanoids. Cholesterol is a sterol synthesized in the liver and consumed in the diet through foods of animal origin.

60 Summary (cont’d) Lipid digestion occurs primarily in the small intestine, facilitated by emulsification by bile acids to form micelles and the action of pancreatic lipase. The transport of lipids in the body occurs by protein-rich lipoproteins, including chylomicrons, very low-density lipoproteins, low-density lipoproteins, and high-density lipoproteins Recommended fat intake is 20% to 35% of the total calories. Recommendations to limit the intake of saturated fat and trans fat intake are given based on their ability to raise blood cholesterol and heart disease risk. Getting the right ratio of essential fatty acids is beneficial for health.


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