• Lipids
Chapter 4
• Lipids
• Low-fat diets do not always mean weight loss
• “Good” (unsaturated)
– Eat in moderation
• “Bad” (saturated fat and trans fats)
– Limited
• 3 classes of lipids
– Triglycerides (fats and oils)
– Phospholipids (e.g., lecithin)
– Sterols (e.g., cholesterol)
– Triglycerides
• Approximately 98% of the fat in foods
• Made of the same elements as carbohydrates
– Carbon, hydrogen, and oxygen
– Proportionately more carbon and hydrogen atoms to oxygen atoms, triglycerides yield more calories per gram than carbohydrates
• Triglycerides (cont’d)
• Fatty acids
– Basically chains of carbon atoms with hydrogen atoms attached
– Vary in the length of their carbon chain and in the degree of unsaturation
– Carbon chain length o Almost all fatty acids have an even number of carbon atoms in their chain o Long-chain fatty acids o Medium- and short-chain fatty acids

• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation o When all the carbon atoms in a fatty acid have four single bonds each, the fatty acid is said to be “saturated” with hydrogen atoms o An “unsaturated” fatty acid does not have all the hydrogen atoms it can potentially hold; therefore, one or more double bonds form between carbon atoms in the chain
 Monounsaturated
 Polyunsaturated
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Fatty acids can attach to glycerol molecules o Types and proportions of fatty acids present influence the sensory and functional properties of the food fat o All food fats contain a mixture of saturated, monounsaturated, and polyunsaturated fatty acids
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Saturated fats
 Tend to be solid at room temperature
• Triglycerides (cont’d)
• Fatty acids (cont’d)
 Animal fats provide approximately 60% of fat in American diet
 The only vegetable fats that are saturated are palm oil, palm kernel oil, and coconut oil

– Degree of saturation (cont’d) o Saturated fats (cont’d)
 Commonly known as a “bad” fat because it raises blood cholesterol levels
 Raises total and LDL cholesterol levels
 As levels rise, risk of coronary heart disease rises
 May also make the inner lining of arteries more prone to inflammation and the buildup of fatty plaques by interfering with the normal protective action of HDL-cholesterol
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats
 Liquid at room temperature
 Monounsaturated fats are the predominant fat in olives, olive oil, canola oil, peanut oil, avocado, cashews, almonds, and most other nuts
 Polyunsaturated fats are the predominant fat in corn, soybean, safflower, and cottonseeds oils, and also in fish
 Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Commonly known as “good fats” because when they are eaten in place of saturated fats they lower LDL-cholesterol and raise HDL-cholesterol
 Position of the double bond
 Part of an unsaturated fatty acid’s identity is determined by the location of the first or only double bond along the carbon chain
 Location of first double bond significant

 Determines essentiality of fatty acid
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Linoleic acid
 The essential n-6 fatty acid
 Especially abundant in plant oils
 Alpha-linolenic acid
 The essential n-3 fatty acid
 Found in flaxseed, canola, soybean, and walnut oils; and in nuts, especially walnuts
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Alpha-linolenic acid (cont’d)
 Can convert alpha-linolenic acid to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the body
 Commonly referred to as “fish oils”
 Stability of fats
 Degree of unsaturation influences the stability of fats
 Polyunsaturated fats are most susceptible to rancidity
– Food manufacturers may add antioxidants or hydrogenate to prolong shelf life
• Triglycerides (cont’d)
• Fatty acids (cont’d)

– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Hydrogenation and trans fats
 Hydrogenation is a process that adds hydrogen atoms to hearthealthy polyunsaturated oils to saturate some of the double bonds so that the resulting product is less susceptible to rancidity and has improved function
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Hydrogenation and trans fats (cont’d)
 1970s
 Process of hydrogenation changes the placement of the hydrogen atoms
 Most trans fat in a typical American diet comes from partially hydrogenated oils and foods made with partially hydrogenated oils
• Triglycerides (cont’d)
• Fatty acids (cont’d)
– Degree of saturation (cont’d) o Unsaturated fats (cont’d)
 Hydrogenation and trans fats (cont’d)
 Trans fats, like saturated fat, raise LDL-cholesterol and lower
HDL-cholesterol
 Ounce for ounce, trans fats are more unhealthy than saturated fats
 FDA labeling must include trans fats
 Trans fats being eliminated from commercial use

• Triglycerides (cont’d)
• Functions of triglycerides in the body
– Primary function of fat is to fuel the body
– Other important functions in the body: o Insulate and cushion internal organs o Help to regulate body temperature o Facilitate the absorption of the fat-soluble vitamins A, D, E, and K when consumed at the same meal
• Triglycerides (cont’d)
• Functions of triglycerides in the body (cont’d)
– Essential fatty acids have specific functions in the body
– Much interest in fish oils o Results of research inconclusive
• Other Lipids

Phospholipids
– Phospholipids have a glycerol backbone with fatty acids attached like triglycerides o Difference is phosphate group replaces one of the fatty acids
– Both fat-soluble (because of the fatty acids) and water-soluble (because of the phosphate group) o Enables them to act as emulsifiers
– Structural components of cell membranes that facilitate the transport of fat-soluble substances across cell membranes
• Other Lipids (cont’d)
• Phospholipids (cont’d)
– Precursors to prostaglandins
– Lecithin is the best-known phospholipid o Supplements unnecessary

o Not an essential nutrient
• Other Lipids (cont’d)

Cholesterol
– A sterol o Waxy substance whose carbon, hydrogen, and oxygen molecules are arranged in a ring
– Occurs in the tissues of all animals o Found in all cell membranes and in myelin
– Found exclusively in animals o Liver and egg yolks are the richest sources
• Other Lipids (cont’d)
• Cholesterol (cont’d)
– “Good” and “bad” cholesterol refer to the lipoprotein packages that move cholesterol through the blood
– Not an essential nutrient
– Dietary cholesterol increases total and LDL-cholesterol
• How the Body Handles Fat
• Digestion
– Minimal amount of chemical digestion of fat occurs in the mouth and stomach through the action of lingual lipase and gastric lipases respectively
– Duodenum o Stimulates the release of the hormone cholecystokinin
 Stimulates the gallbladder to release bile
 Prepares fat for digestion
• How the Body Handles Fat (cont’d)
• Digestion (cont’d)
– Most fat digestion occurs in the small intestine

– End products of digestion are absorbed into intestinal cells
– Small amount is excreted in feces
– Digestion of phospholipids is similar
– Cholesterol does not undergo digestion; it is absorbed as is
• How the Body Handles Fat (cont’d)
• Absorption
– About 95% of consumed fat is absorbed
– Small fat particles are absorbed directly through the mucosal cells into capillaries
– Absorption of larger fat particles, namely monoglycerides and long-chain fatty acids, is more complex o Micelles o Recombine into triglycerides o Chylomicrons distribute dietary lipids throughout the body
• How the Body Handles Fat (cont’d)
• Fat catabolism
– Catabolism of fatty acids increases when: o Carbohydrate intake is inadequate (e.g., while on a very low-calorie diet) o Or catabolism of fatty acids is unavailable (e.g., in the case of uncontrolled diabetes)
– Fatty acids cannot be reassembled to make glucose
– Inefficient choice of fuel for glucose-dependent brain cells, nerve cells, and red blood cells
– How the Body Handles Fat (cont’d)
• Fat anabolism
– Most newly absorbed fatty acids recombine with glycerol to form triglycerides that end up stored in adipose tissue

– Fat stored in adipose tissue represents the body’s largest and most efficient energy reserve
– Adipose cells have a virtually limitless capacity to store fat
– Fat reserves
• Fat in Foods o 1 pound of fat provides 3,500 calories
• Vital functions of fat
– Imparts its own flavor, from the mild taste of canola oil and corn oil to the distinctive tastes of peanut oil and olive oil
– Transfers heat to rapidly cook food, as in the case of frying
– Absorbs flavors and aromas of ingredients to improve overall taste
– Adds juiciness to meats
• Fat in Foods (cont’d)
• Vital functions of fat (cont’d)
– Creates a creamy and smooth “mouth feel” in items such as ice cream, desserts, and cream soups
– Adds texture or body to many foods, such as flakiness, tenderness, elasticity, and viscosity; for example, milk is watery and cheese is rubbery when fat is removed
– Imparts tenderness and moisture in baked goods, such as cookies, pies, and cakes, and delays staling
– Is insoluble in water, thus providing a unique flavor and texture to foods such as salad dressings
• Fat in Foods (cont’d)
• Fat content in MyPyramid varies greatly among groups and between selections within each group
– Generally, three MyPyramid food groups provide little or no fat o Grains naturally contain very little fat o Unadulterated vegetables contain little or no fat

o Fruits, with the exception of avocado, coconut, and olives, are naturally fat-free
• Fat in Foods (cont’d)
• Milk
– Classified into one of 3 subgroups: full fat, reduced fat, and fat free o Fat in dairy products is predominately saturated and full-fat products have more cholesterol than in the lower-fat options o Fat-free varieties of milk, yogurt, and cheese provide virtually no fat o The midrange is reserved for reduced-fat items—they have some of the fat and cholesterol removed yet retain some of the “mouth feel” characteristic of whole milk
• Fat in Foods (cont’d)
• Meat and beans
– 4 subgroups based on fat content
– Details worth noting: o The 1-oz. size cited in MyPyramid is simply a reference, not a serving size or a portion size; typically, a serving size (amount recommended for a meal) is 3 to 4 oz., and a portion size (amount actually eaten at one time) may be much larger o Fat added during cooking, such as frying or basting with fat, increases the overall fat content and counts as choices from the Oils group; it is recommended that meats be prepared by methods that do not add fat, such as baking, roasting, broiling, grilling, poaching, or boiling
• Fat in Foods (cont’d)
• Meats and fat content
– Untrimmed meats are higher in fat than lean-only portions
– “Red meats,” namely beef, pork, and lamb, are higher in saturated fat than the “white meats” of poultry and seafood
– White poultry meat is lower in fat than dark meat; removing poultry skin removes significant fat
– Fat content varies among different cuts of meat. The leanest cuts are beef loin and round; veal and lamb from the loin or leg; and pork tenderloin or center loin chop.

• Fat in Foods (cont’d)
• Meats and fat content (cont’d):
– Beef grades can be used as a guide to fat content because grades are based largely on the amount of marbling
– Shellfish are very low in fat but have considerable cholesterol
– Most wild game is very lean; the fat content in bison, venison, elk, ostrich, pheasant
(without skin), rabbit, and squirrel ranges from 2 to 5 g per 3-oz. serving
– Processed meats, such as sausage and hot dogs, may provide more fat calories than protein calories
• Fat in Foods (cont’d)
• Nuts and fat content:
– Nuts have many healthy attributes; they contain plant protein, fiber, vitamin E, selenium, magnesium, zinc, phosphorus, and potassium, in a low–saturated-fat, cholesterol-free package o Nuts’ high-fat content of 13 to 20 g/oz. comes mostly from monounsaturated fats and polyunsaturated fats; walnuts are a rich source of alpha-linolenic acid
• Fat in Foods (cont’d)
• Cholesterol in foods
– Egg yolks have approximately 213 mg of cholesterol. The cholesterol content of typical cuts of beef, pork, lamb, and poultry is generally around 70 mg/3 oz. Veal averages slightly more at about 90 mg/3 oz. The exceptions are organ meats, which are very high in cholesterol. Egg whites, dried peas and beans, are nuts are cholesterol-free.
• Fat in Foods (cont’d)
• Oils
– Allowances are small
– Some items on the oils list actually are included in other groups also
• Dietary Reference Intakes
• The issue of how much of each particular type of fat is needed, how much is optimal, and how much is too much is complex and in some cases controversial

• Total fat
– Neither an AI or RDA is set for total fat due to insufficient data
– An acceptable macronutrient distribution range (AMDR) is estimated to be 20% to 35% of total calories for adults
• Dietary Reference Intakes (cont’d)
• Saturated and trans fat
– Additional macronutrient recommendation issued for both of these fats is that intake should be as low as possible within the context of a nutritionally adequate diet
– Neither of these fats needs to be consumed in the diet
• Dietary Reference Intakes (cont’d)
• Essential fatty acids
– Both an acceptable macronutrient distribution range and adequate intakes have been set for the essential fatty acids linoleic acid and alpha-linolenic acid
– AI should not be confused with recommended dietary allowance
– Essential fatty acid deficiency o Body cannot make essential fatty acids o Symptoms of essential fatty acid deficiency include growth failure, reproductive failure, scaly dermatitis, and kidney and liver disorders
• Dietary Reference Intakes (cont’d)
• Cholesterol
– The additional macronutrient recommendation issued for cholesterol is that intake be as low as possible
– Fat in Health Promotion
• Message to eat less fat was too simplistic
• Type of fat in the diet can affect serum lipids more than the total amount of fat
• Eat less saturated fat and keep trans fat consumption as low as possible
– To cut saturated fat intake, experts recommend:

o Limiting meat intake, especially red meat, and choosing lean varieties o Reduced- or no-fat dairy products o Hydrogenated fats should be avoided
• Fat in Health Promotion (cont’d)
• Limit total fat and go for unsaturated fats
– Most effective way to limit total and saturated fat and increase unsaturated fats may be with a plant-based diet
• Limit cholesterol
– Cholesterol intake becomes less important when saturated fat intake is low
• What about “fish oils?”
– American Heart Association suggests healthy people eat at least 2 servings of fish per week
– Fish oil pills are an alternative source of omega-3 fats