Role in Wellness

It may be time for a truce about the consumption of dietary fat. Since the 1970s consumption of fats gained a negative reputation as a possible source of diet-related disorders and a factor in the increasing waistlines of Americans. We are now recognizing that the types and amount of fats being consumed determine the impact on our bodies. Some dietary fats are essential, while others are not. Some actually confer additional benefits for health, and a few, when eaten in large amounts, may increase the risk of certain diseases. This chapter explores these issues.

Fat is valuable and necessary to health. It is important to learn about fat in food, what the fat we eat does in our bodies, and how it can be both helpful and harmful to our health. Individual preference for fat is developed either in infancy or early childhood; innate preferences for sweet taste are observed at birth.¹ Thus children learn to prefer tastes, flavors, and textures that are associated with foods that are rich in fat, sweet, or both. Aging may be associated with increasing acceptance of bitter tastes and consumption of more fruits, vegetables, and whole grains.¹ Nonetheless, decreasing fat consumption takes time and effort, perhaps because of food selection habits, symbolic meaning associated with certain foods, and sensory values of fats in foods.

The five dimensions of health provide ways to think about the effects of changing dietary fat consumption. Physical health is maintained by consuming dietary fats that are necessary for essential fatty acids, for energy, and for fat-soluble vitamins. Excessive intake of fats, though, may increase the risk of obesity and diet-related diseases. The intellectual health dimension encompasses the skills necessary to assess the type of dietary fat modification most appropriate for our clients’ and our own health needs. How we emotionally approach nutritional lifestyle changes for our clients and ourselves affects success, which reflects the emotional health dimension. Can these emotions be expressed, or are changes simply disregarded because they make us feel uncomfortable? The social dimension is tested as change is initiated. Are relationships of family and friends based on sharing high-fat meals? Can you or your clients refuse to take part in social situations without jeopardizing relationships or making others feel defensive? Can food preparation suggestions to lower the fat content be made without seeming overly critical? Some religions maintain that taking care of one’s body is necessary to achieve spiritual goals. Adopting a healthier fat intake supports these spiritual health dimension goals.

Fat actually refers to the chemical group called lipids. Lipids are divided into three classifications: fats (or triglycerides), and the fat-related substances of phospholipids and sterols. Triglycerides are the largest class of lipids and may be in the form of fats (somewhat solid) or oils (liquids). Approximately 95% of the lipids in foods and in our bodies are in the triglyceride form of fat. The other two lipid classifications are the fat-related substances of phospholipids and sterols. Lecithin is the best-known phospholipid; cholesterol is the best-known sterol. All are organic—composed of carbon, hydrogen, and oxygen—and cannot dissolve in water.

Functions

The functions of lipids may be divided into two categories: (1) specific characteristics of foods caused by lipids and (2) maintenance of the physiologic health of our bodies.

Food Functions

Source of Energy

Fat is the densest form of stored energy in food and our bodies. This means that gram for gram, food fat—in the form of triglycerides—can produce more than twice the energy in kcal as carbohydrate or protein. For example, a gram of nearly pure fat (9 kcal), such as butter, provides more than twice the kcal as a gram of nearly pure carbohydrate (4 kcal), such as sugar, or a gram of nearly pure protein (4 kcal) such as dried, lean fish.

Palatability

Fat makes food smell and taste good. Deep-fat fried potatoes outrank all other vegetable choices among North Americans. Whether it’s bread with butter (or margarine), salad with dressing, or desserts with cream, fat makes these foods taste pleasant for many people. For patients who are anorectic because of illness, strategically adding small amounts of fats to meals may increase their nutrient intake.

Satiety and Satiation

Fat helps prevent hunger between meals. Fat slows down digestion because of the hormones released in response to its presence in the gastrointestinal (GI) tract, causing us to feel full and satisfied; we call this feeling satiety. Satiation is another, different aspect of fat consumption that occurs during, not after, eating. In contrast to satiety, satiation tends to increase our desire to eat additional fatty foods, not less. The effect of fat on satiation is likely to be more important than its effect on satiety and may lead to overeating.² A situation that often occurs with the last slice of pizza provides a good example: You want it, you eat it, and half an hour later, you feel too full.

Food Processing

Certain qualities of lipids, besides their nutritional purposes, make them a valuable resource for the processing of foods. The use of processed hydrogenated fats helps keep the fat in food products from turning rancid. Lecithin, a phospholipid, has an extensive role as an emulsifier. An emulsifier is a substance that works by being soluble in water and fat at the same time. These functions, which will be described in more detail, also increase our overall intake of lipids by allowing their use in numerous processed foods.

Nutrient Source

Some fats contain or transport the fat-soluble nutrients of vitamins A, D, E, and K and the essential fatty acids of linoleic and linolenic fatty acids.

These essential fatty acids (EFAs), components of fat triglycerides, are polyunsaturated fatty acids that cannot be made in the body and must be consumed in the diet. EFAs are necessary materials for making compounds, such as prostaglandins, that regulate many body functions, including blood pressure, blood clotting through platelet aggregation, gastric acid secretions, and muscle secretions. The overall strength of cell membranes depends on EFAs.

Overt deficiency symptoms of EFAs include skin lesions and scaliness (eczema) caused by increased permeability, which leads to membrane breakdown throughout the body (Figure 5-1). Inflammation of epithelial tissue and increased susceptibility to infections throughout the body are also possible. Because the minimum amount of EFA required is contained in only about 2 teaspoons of polyunsaturated vegetable oil, deficiencies of EFAs were thought to be rare. However, deficiencies have been noted in (1) older patients with peripheral vascular disease (a potential complication of diabetes mellitus); (2) patients with fat malabsorption, such as cystic fibrosis; and (3) patients receiving treatment for protein malnutrition with low-fat, high-protein diets. Individuals recovering from serious accidents and burns are also at risk.³ It is possible that individuals who strive to achieve extremely low dietary fat intake for health reasons or from disordered eating could develop EFA deficiencies.

Triglyceride is the largest class of lipids found in food and body fat. Triglycerides are compounds consisting of three fatty acids and one glycerol molecule (Figure 5-2). The glycerol portion is derived from carbohydrate, but it is a small part compared with the fatty acids that may be alike or different from each other. Fatty acids can be made of long or short chains of carbon atoms. Each carbon atom has four bonding sites or imaginary arms where it can attach to other atoms. To form a carbon chain, one site on each side of the carbon bonds to a neighboring carbon, as if one arm on each side were outstretched to form a chain. Because these atoms have four arms, the two extra arms each attach to a hydrogen atom, which makes the chain saturated with hydrogen.

If a hydrogen atom is removed from two neighbor carbons, freeing the extra arm on each, the carbons are bonded to each other at two sites. The two arms on the same side both clasp the two arms of the neighboring carbon, forming a double bond. We call this an unsaturated carbon chain because there is a possibility that hydrogen could come along and saturate the chain by breaking one set of clasped arms and attaching to them. In foods, this is sometimes done artificially through the process of hydrogenation, which forces hydrogen atoms to break a double bond and attach to the carbons, creating a saturated fat (Figure 5-3). Hydrogenation is discussed in the section on processed fats.

All natural fats are mixtures of different types of fatty acids. Plants contain mostly polyunsaturated fats, but most plant oils contain some saturated fatty acids (Figure 5-4). Animal fats, though high in saturated fats, contain amounts of polyunsaturated fats. The predominant type of fat in a food determines its category.

A saturated fatty acid has a single-bonded carbon chain that is fully saturated because hydrogen atoms are attached to all available bonding sites. Palmitic acid (16 carbon atoms) (Figure 5-5, A), a saturated fatty acid, is contained in meats, butterfat, shortening, and vegetable oils. Other saturated fatty acids include stearic acid (18 carbon atoms), myristic acid (14 carbon atoms), and lauric acid (12 carbon atoms).² Additional food sources of saturated fatty acids are primarily animal, including beef, poultry, pork, lamb, luncheon meats, egg yolks, and dairy products (milk, butter, and cheeses); the only major plant sources are palm and coconut oils (often called tropical oils) and cocoa butter.

Unsaturated fatty acids have one or more unsaturated double bonds along the carbon chain. If a carbon chain has only one unsaturated double bond, it is a monounsaturated fatty acid. Oleic acid (see Figure 5-5, B) is the main monounsaturated fatty acid in foods. Dietary sources include olive oil, peanuts (peanut butter and peanut oil), and canola oil.

If a carbon chain has two or more unsaturated double bonds, it is a polyunsaturated fatty acid (PUFA). Food sources include vegetable oils (corn, safflower, wheat germ, canola, sesame, and sunflower), fish, and margarine.

PUFAs are categorized by the location of the unsaturation in the molecular structure of the fatty acid. Two categories of polyunsaturated fatty acids, omega-6 and omega-3, contain two fatty acids (linoleic and linolenic) that our bodies cannot manufacture; these acids are EFAs and must be provided by dietary intake. The characteristic that distinguishes them from other PUFAs is the position of the final double bond in relation to the end of the carbon chain. The final double bond is at the sixth carbon from the omega end of the chain in linoleic acid (see Figure 5-5, C), the main member of the omega-6 family. The first double bond is at the third carbon atom from the omega end in linolenic acid (see Figure 5-5, D), the main member of the omega-3 family.

Americans consume an abundance of linoleic acid from consumption of large amounts of vegetable oils, such as margarine and salad dressing, and large amounts of prepared foods. Another source of linoleic acid may be animal foods; for example, although poultry fat is predominantly saturated, it also contains some PUFA, including linoleic acid.

In contrast, American consumption of linolenic acid is not abundant at all. Linolenic acid is associated with fish consumption because that is how it was first recognized as important in health. A low incidence of heart disease among the native people of Greenland and Alaska, in spite of a very high-fat diet, was traced to the oils in deep-water fish, the staple in their diet.⁴ One of the main omega-3 fatty acids in fish is eicosapentaenoic acid (EPA), which is derived from linolenic acid. Fish are more efficient in this conversion of fatty acids than humans. Omega-3 fatty acids appear to lower the risk of heart disease by reducing the blood clotting process; clots can cause blockages in the arteries if plaques exist. Although consuming extra omega-3 fatty acids is likely to have little effect on blood cholesterol levels, it may reduce the risk of clots that may cause a myocardial infarction (heart attack) and possible sudden death.³ According to prospective studies, reduced risk of coronary artery disease (CAD), because of higher consumption of fish or omega-3 fatty acids, appears applicable to men and women.^3,4

Certain fish provide more omega-3 fatty acids than others. Good sources include tuna, salmon, bluefish, halibut, sardines, and rainbow trout. Table 5-1 lists additional sources. Eating fish twice a week or using canola oil, another source of linolenic acid, should provide an adequate balance between sources of omega-6 and omega-3 fatty acids, although the best balance is still unknown.

Inuits consume 4 to 5 g of EPAs daily,⁵ about the amount in 1.5 to 3 pounds of certain deep-water fish. Because it is unlikely that most Americans will consume this quantity of fish, fish oil supplements of these fatty acids are manufactured. However, questions about proper dosages, safety, and side effects are still being researched. Symptoms that may potentially occur from high intakes of omega-3 fatty acids include infections and increased bleeding time, and may affect blood glucose levels of individuals with diabetes.³ For now, the best approach is to increase consumption of foods containing these potentially important fatty acids, unless a health care professional prescribes fish oil supplements, indicating dose levels.

Phospholipids

Phospholipids are lipid compounds that form part of cell walls and act as a fat emulsifier. Similar to triglycerides, phospholipids contain fatty acids, but they have only two fatty acids; the third spot contains a phosphate group. The body manufactures phospholipids, found in every cell; therefore, they are not essential nutrients. Lecithin, the main phospholipid, contains two fatty acids, with the third spot filled by a molecule of chloline plus phosphorus (Figure 5-6). In the body, lecithin’s function as an emulsifier is to work by being soluble in water and fat at the same time.

Lecithin from soybeans is used in food processing to perform an emulsification role. Lecithin, naturally found in egg yolks, is the versatile ingredient in mayonnaise that prevents separation of vinegar and oil. Lecithin is also used in manufacturing chocolates to keep the cocoa butter and other ingredients combined and in cakes and other bakery products to maintain freshness.

Sterols

Sterols, a fatlike class of lipids, serve vital functions in the body. Sterol structures, including cholesterol, are carbon rings intermeshed with side chains of carbon, hydrogen, and oxygen, which make them more complex than triglycerides (Figure 5-7). Like phospholipids, sterols are synthesized by the body and are not essential nutrients. For example, if dietary cholesterol is not consumed, the liver will produce the amount required for body functions.

Generally, dietary cholesterol accounts for about 25% of the cholesterol in the body. The rest, which is made in the liver, seems to be produced in relation to how much is needed. The only food sources of cholesterol are animal and include beef, pork (bacon), chicken, luncheon meats, eggs, fish, and dairy products (milk, butter, and cheeses); plant foods do not contain cholesterol.

The mouth’s primary fat digestive process is mechanical, as teeth masticate fatty foods. The glands of the tongue produce a fat-splitting enzyme (lingual lipase) released with saliva that begins digestion of long-chain fatty acids such as those found in milk.

Small Intestine

Fats entering the duodenum initiate the release of cholecystokinin (CCK) hormone from the duodenum walls. CCK, as described in Chapter 3, then sparks the gallbladder to release bile into the small intestine. The bile emulsifies fats to facilitate digestion. Mechanical digestion through muscular action allows for increased exposure of the emulsified fat globules to pancreatic lipase. This enzyme is the primary digestive enzyme that breaks triglycerides into fatty acids, monoglycerides, and glycerol molecules. Note that fats may not be completely broken down. Some may also pass through without being digested or absorbed. Figure 5-8 summarizes digestion of triglycerides.

Fat Intake and Issues

Awareness of the fat content of foods is steadily growing. Whether we are consuming a sophisticated gourmet feast or chowing down on hot dogs and hamburgers at a summer barbecue, the fat levels of our meals may be of interest. Concerns about fat in our diets center around health issues of excessive intake of energy, excessive fat intake that replaces other nutrients, and the relationship between dietary fat intake and the development of chronic diet-related diseases. Some lipids consumed in foods are essential to our bodies to achieve wellness.

Fat Content of Foods

High-fat foods are almost always high-calorie foods. This is because fats are the most concentrated source of food energy, supplying 9 kcal/g; carbohydrates and proteins supply 4 kcal/g. Because most foods contain a mixture of nutrients, we can identify the fat content of food by the number of fat grams in a serving or the percent of daily value of recommended fat intake in a serving. Nutritional labels on packaged food contain this information.

The Dietary Reference Intakes (DRIs), based on Acceptable Macronutrient Distribution Ranges (AMDRs), recommend that we eat 20% to 35% of our kcal intakes from fats, with 10% or less of kcal from saturated fats.⁶ Based on the daily values, total fat intake for an average daily kcal intake of 2000 to 2500 kcal should range from about 40 to 97 g or less (400 to 875 kcal or less). Saturated fat should be 25 to 20 g or less (225 to 180 kcal or less).

There is evidence that diets with fat levels of 18% to 22% may have undesirable effects, including lower high-density lipoprotein (HDL) levels and higher triglyceride levels.⁷ The evidence does not support reducing fat much below 26% kcal as fat—not a problem for most Americans, who have a long way to go toward lower-fat diets. In fact, most Americans are still within the 30% to 40% of total energy intake as fat, even though many believe they are avoiding or limiting high-fat foods.³ One reason may be because high-fat foods have both potent sensory qualities and high-energy density; overeating is then often more passive than active. Another reason is that people who eat a lot of high-fat foods are unsure whether their diets are high in fat because home cooking has fallen sharply; the cook no longer knows exactly what goes into each dish. Also, portion sizes at restaurants are often twice the size of that recommended for good health by MyPyramid. Then there is the “less fat, more carbs” message that has been incorrectly translated into sweet, kcal-dense, low-fiber carbohydrate foods, so the low-fat diet has become a high-calorie, processed-carbohydrate diet. It is also likely that people are misled by labels of “reduced fat” foods and thus actually increase the total intake of such foods. The individual foods we eat daily may have a higher or lower fat content, but overall we should generally average 25% to 30% of kcal fat intake from all the foods we eat each day (see the Teaching Tool box, Calculating Your Daily Fat Intake).

 Teaching Tool

Calculating Your Daily Fat Intake

Use the following steps to calculate your daily grams of fat:

1. Use the Recommended Energy Intake chart in Chapter 9 to determine your appropriate energy needs for the day. Multiply that number of kcal by 0.25 for 25% fat intake or by 0.30 for 30% fat intake.

2. Divide that number by 9, because each gram of fat has 9 kcal. For example, if you consume 1800 kcal a day and want to get 25% of those kcal from fat: 0.25 × 1800 = 450. Then divide 450 by 9 to get 50 g of fat. Energy needs for the day kcal × 0.30 = kcal fat intake/day. Kcal fat intake a day/9 kcal = g of fat/day.

3. Next, check food labels and/or use food composition tables (see Appendix A) for the grams of fat per food serving. You then can compare the sum of the fat grams consumed with the recommended levels for your particular energy needs.

How do we measure the fat in foods without labels, such as fresh foods, home-cooked recipes, and restaurant items? One way is to classify foods into groups according to fat content. The Exchange List uses this system by listing protein foods based on their “leanness” (see Chapter 2 or Appendix A). In contrast, MyPyramid devotes a section to oils (fats that are liquid at room temperature) and provides information on the dietary fat content of foods in the oil category as well as foods in fruit, meats, and bean categories that contain oils. Oils are not considered a food group but are recognized as needed for good health. MyPyramid emphasizes the health-promoting oils from plants and fish, rather than the solid, more saturated fats from palm kernel oil and coconut oil and many animal foods and from hydrogenation of vegetable oils. As shown in Box 5-1, frequently consumed oils are canola, corn, olive, cottonseed, safflower, and soybean. Foods listed as good sources of oils consist of nuts, certain fish, avocado, and olives. Table 5-2 provides examples of fat in servings from different foods. Common solid fats include butter, lard (pork fat), shortening, beef fat (suet, tallow), stick margarine, and chicken fat.

BOX 5-1   MyPyramid

Oils

MyPyramid focuses on oils, which are fats that are liquid at room temperature. Oils come from plant sources and fish. Common plant oils that do not contain cholesterol or saturated fats include canola, corn, olive, cottonseed, safflower, soybean, and sunflower. A few plant oils such as palm kernel oil and coconut oil contain saturated fats, making them more similar in function to solid fats such as those found in animal-derived foods.

Some foods that are naturally high in oils contain monounsaturated and/or polyunsaturated fat. These include nuts, avocado, olives, salmon, and tuna.

Solid fats are solid at room temperature. Solid fats primarily come from animal foods and can be made from plant oils when hydrogenated. Solid fats include butter, beef fat (tallow, suet), chicken fat, pork fat (lard), and processed hydrogenated stick margarine and vegetable shortening. Hydrogenated fats usually contain trans fat, which are identified on nutrition labels.

The focus of this MyPlate box is on portions of oils.

How Do I Count the Oils I Eat?*

The following table gives a quick guide to the amount of oils in some common foods.

FAT	AMOUNT OF FOOD	AMOUNT OF OIL (TEASPOONS/GRAMS)	KCAL FROM OIL (APPROXIMATE)	TOTAL KCAL (APPROXIMATE)
Oils
Vegetable oils (such as canola, corn, cottonseed, olive, peanut, safflower, soybean, and sunflower)	1 Tbsp	3 tsp/14 g	120	120
Foods Rich in Oils
Margarine, soft (trans fat-free)	1 Tbsp	tsp/11 g	100	100
Mayonnaise	1 Tbsp	tsp/11 g	100	100
Mayonnaise-type salad dressing	1 Tbsp	1 tsp/5 g	45	55
Italian dressing	2 Tbsp	2 tsp/8 g	75	85
Thousand Island dressing	2 Tbsp	tsp/11 g	100	120
Olives, ripe, canned	4 large	tsp/2 g	15	20
Avocado†	medium	3 tsp/15 g	130	160
Peanut butter†	2 Tbsp	4 tsp/16 g	140	190
Peanuts, dry-roasted†	1 oz	3 tsp/14 g	120	165
Mixed nuts, dry-roasted†	1 oz	3 tsp/15 g	130	170
Cashews, dry-roasted†	1 oz	3 tsp/13 g	115	165
Almonds, dry-roasted†	1 oz	3 tsp/15 g	130	170
Hazelnuts†	1 oz	4 tsp/18 g	160	185
Sunflower seeds†	1 oz	3 tsp/14 g	120	165

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