Nutrients in Animal Products and Their Bioavailability
Data on the nutrient content of the food supply provide information about the contribution of various food groups to nutrients available for consumption. This series is computed and reported by the U.S. Department of Agriculture (USDA). It is designed to study trends in the levels of nutrients since the early part of the century and changes in food sources of these nutrients. The data have the same limitations as the food supply data in that they are not adjusted for spoilage, trimming, waste, or cooking loss. They measure the nutrients available for consumption by the population rather than nutrient intake. Except for a few processed fruits and vegetables, nutrient values are based on raw food values.
The nutrients consumed represent only a fraction of those present in the food supply. Numerous factors, including metabolic, physiological, and nutritional parameters, all influence the absorption, digestion, and ultimate utilization of nutrients within a food. The bioavailability of a nutrient may not be equivalent in all food sources due to the nutrient's altered chemical state or to associated factors within the food or within the meal that cause the nutrient to be in a more available or less available form. For instance, in dairy products, calcium is present with lactose, a carbohydrate that enhances calcium's absorption. Some vegetable sources such as spinach also contain considerable amounts of calcium, but the presence of oxalates, which bind calcium as insoluble salts, prevents much of its absorption.
Animal products contribute significantly to the total nutrients in the food supply (Table 2-1 and Figure 2-1). They are a primary source of vitamins B12 and B6, riboflavin, niacin, zinc, phosphorus, and calcium and account for 68 percent of the protein available in the food supply.
TABLE 2-1
Selected Nutrients Provided by Animal Products, 1985 (in percent).
Figure 2-1
Selected nutrients provided by animal products (in percent). See also Table 2-1. Source: Human Nutrition Information Service, U.S. Department of Agriculture, unpublished data, 1987. (The nutrient composition values for meats are not updated. A revision (more...)
Calories
Overall, animal products provide about 36 percent of the calorie content of the food supply while contributing more than a third of the iron, vitamin A, thiamine, and magnesium content; about half of the niacin, riboflavin, and vitamin B6 content; more than 70 percent of the zinc content; more than 80 percent of the calcium content; and nearly 100 percent of the vitamin B12 content.
Red meats account for the largest proportion of the calories (about 15 percent), followed by dairy products (10 percent), animal fats (4 percent), poultry (3.5 percent), eggs (1.6 percent), and fish and shellfish (0.9 percent). From 1977 to 1985, the total calories available per capita in the food supply have increased by 7 percent, from 3,330 to 3,560. This parallels an increase in caloric intake indicated by dietary survey data from 1977 to 1985 for children ages 1 to 5 years of 8.3 percent, women ages 19 to 50 years of 5.6 percent, and men ages 19 to 50 years of 15 percent.
In the 1977-1978 Nationwide Food Consumption Survey (NFCS), animal products contributed an average of about 45 percent of total calories to the diets of all individuals, with dairy products accounting for about 14 percent; meat, poultry, and fish about 28 percent; and eggs 2.4 percent (Table 2-2). The meat, poultry, and fish group was the primary source of calories for adults, contributing 24 to 34 percent of total intake. Children of ages 3 to 14 years derived slightly fewer calories from this category (20 to 25 percent) and more from the dairy and grain products groups than did adults.
TABLE 2-2
Contribution of Animal Products to Total Calories in the Diet Based on 3-Day Intake (in percent).
It is possible that the fat, and therefore the calories, derived from meats, poultry, and fish is overstated in the NFCS analysis. In analyzing the dietary survey responses, if an individual did not specify whether he or she ate the separable fat on meat or the poultry skin, the methodolgy stipulated that it be assumed that all these components were eaten. The American Meat Institute study (Stanton, 1987) addresses this issue.
Protein
The protein from animal products differs in several respects from that from vegetable sources. First, animal products are richer than vegetable sources of the eight essential amino acids, those components of proteins that cannot be synthesized by the body and must be supplied in food. Animal products provide almost three-fourths of the eight essential amino acids in the food supply and contribute about 67 percent of the total protein, reflecting the greater concentration of these vital nutrients (Table 2-3) (Link-swiler, 1982).
TABLE 2-3
Percentage of Contribution of Essential Amino Acids from Animal Products to Total Essential Amino Acids in the U.S. Food Supply.
Few proteins from either animal or vegetable sources are consumed without some further processing, usually cooking. How this affects the bioavailability of the proteins for utilization by the body is important, particularly when estimating the amount of protein available in the food supply. Proper cooking facilitates digestion and utilization by partially breaking down the protein structure. Excessive or prolonged heating, however, may actually produce new chemical bonds, decreasing the digestibility of the protein. An example is the decreased physiological availability of lysine, tryptophan, and other amino acids in toasted cereal products (Love, 1982). Lysine, for example, under high heat, links with carbohydrate to form a bond resistant to cleavage. Severe heating of animal proteins has also been shown to destroy cystine and result in reduced digestibility and availability of amino acids (Cheftel, 1977).
From the food supply data, about 102 grams of protein are available per capita, with 68.5 percent derived from animal products. Of this amount, red meat contributes the largest percent (27.6), followed by dairy products (20.9) and poultry (11.2), with the fish/shellfish and egg groups contributing about 4.6 and 4.2 percent, respectively. The trend in the percentage of calories from protein, fat, and carbohydrate in the food supply from 1957 to 1984 is evident in Table 2-4.
TABLE 2-4
Sources of Food Energy in the U.S. Food Supply for Selected Years (in percent).
In line with the per capita disappearance data, animal products contributed about 70 percent of the protein in the 1977-1978 NFCS (Table 2-5). The red meat, poultry, and fish group was the largest source of protein, contributing 40 to 56 percent of the protein in the diets of adults and 35 to 39 percent of the protein in children's diets. Eggs accounted for roughly 3 to 5 percent of the total protein in the diets of most age and sex groups, except for elderly males, who derived 6 percent of their daily protein from eggs. Table 2-6 compares NFCS and Continuing Survey of Food Intake by Individuals (CSFII) data in terms of the percentage of calories from protein and fat.
TABLE 2-5
Contribution of Animal Products to Protein in the Diet Based on 3-Day Intake (in percent).
TABLE 2-6
Calories from Protein and Fat (in percent).
Fat, Saturated Fatty Acids, and Cholesterol
Although animal products are important sources of many nutrients, they are also a significant source of fat. On a raw basis, animal products account for 57 percent of the fat available for consumption (Table 2-1). However, the data based on nutrients in raw food may overstate the fat eaten as part of meat products because meats lose substantial amounts of fat during cooking. This is not true for foods like milk and milk products or grains. Waste is also an important consideration when trying to determine food sources of fat. For example, all the separable fat on meat may not be consumed.
Data from the food supply indicate that the contribution of fat from animal sources has been decreasing, while that from vegetable sources has been increasing (Figure 2-2). Changes in the level and sources of fat in the food supply have also affected the fatty acid content. Table 2-7 presents trend data on the percentage of saturated fatty acids and two unsaturated fatty acids (oleic and linoleic) in the food supply.
Figure 2-2
Fat from animal versus vegetable sources in the U.S. food supply for selected years (in percent). Source: Data from N. R. Raper, and R. M. Marston. 1986. Levels and sources of fat in the U.S. food supply. Pp. 127-152 in Dietary Fat and Cancer, C. Ip, (more...)
TABLE 2-7
Selected Fatty Acids in the U.S. Food Supply (in percent).
Knowledge of the fatty acid composition of dietary fats (visible/invisible) is important because different fatty acids, both saturated and unsaturated, exert different metabolic or physiological effects. Also, in some instances the effects of certain component fatty acids are not known.
Except for milk fat (butterfat), most animal fats contain palmitic and stearic acids as the major saturated fatty acids. In addition, milk fat contains significant amounts of short-chain (C4, C6) and medium-chain (C8, C10, C12) fatty acids (Table 2-8). (The nomenclature used to describe a fatty acid includes carbon chain length and numbers of double bonds, if present. For example, an 18-carbon fatty acid with one double bond would be written as C181; an 18-carbon fatty acid without double bonds, that is, completely saturated, would be written as C180.) Current evidence indicates that different dietary saturated fatty acids may have different physiological effects. For example, stearic acid (C180) has negligible effects on serum cholesterol levels as compared to palmitic acid (C160) (Hegsted et al., 1965; Keys et al., 1965). Furthermore, the metabolic effects of the short- and medium-chain fatty acids of milk fat have not been determined, and it is questionable whether they should be grouped (for nutritional considerations) with the saturated fatty acids with known hyperlipidemic effects, such as palmitic acid.
TABLE 2-8
Fatty Acid Composition of Selected Fats and Oils, Expressed as Percentage of Total Fatty Acids.
Oleic acid (C181), a major fatty acid component of animal fats, has hypocholesterolemic (cholesterol-lowering) effects (Grundy, 1986), and therefore in moderate amounts is not considered to be an undesirable dietary fatty acid. All animal fats contain polyunsaturated fatty acids, usually in relatively small amounts (Table 2-8). The common tendency to broadly categorize all animal fats as high in saturated fatty acids is inaccurate; animal fats are made up of a mixture of saturated and unsaturated fatty acids, as shown in Table 2-8. The potential physiological effects of animal fats containing significant amounts of stearic (C180), oleic (C181), short-chain fatty acids, or all three need to be evaluated.
Contrary to popular opinion, vegetable oils rank as one of the primary sources of saturated fatty acids in the food supply. As shown in Table 2-8, vegetable oils such as coconut, palm, and palm kernel oils are as much or more saturated than most animal fats, and considerable amounts are used in commercial baking and as frying fats. Other vegetable oils contain a smaller percentage of saturated fatty acids, but contribute substantially to the total because of the volume in which they are consumed.
Data on the contribution of animal products to total dietary fat from the 1977-1978 NFCS are presented in Table 2-9. Dietary levels of fat averaged 41 percent of total calories for the survey population. More than 63 percent of the total fat was derived from three groups of animal products: 42 percent from red meats, poultry, and fish; 17 percent from milk and milk products; and 4 percent from eggs.
TABLE 2-9
Contribution of Animal Products to Fat in the Diet Based on 3-Day Intake (in percent).
In the 1977-1978 NFCS, red meats provided the major source of fat (32 to 49 percent) in the diets of all age groups other than infants. The contribution of red meat, poultry, and fish to total fat was highest for men and women ages 35 to 50. However, males ages 15 to 18 derived a smaller proportion of fat from the red meat group and a greater proportion from milk and milk products than did adult males. These young males had the highest fat intake of any group. Grains, milk, and milk products contributed roughly comparable amounts of fat to the diets of adults (11 to 15 percent). These food groups were greater sources of fat for children and teenagers than for adults.
Within the meats group, beef was the primary source of fat for most age and sex groups, particularly adult males (Table 2-10). Males ages 19 to 50 derived 17 percent of their dietary fat from beef, compared with 15.2 percent for females of the same age. Poultry was a slightly more important source of fat for women than for men. Pork contributed proportionately more to fat intake for children ages 1 to 5 than for other ages. This age group consumed a greater proportion of its meat in the form of processed pork, in particular, frankfurters and bologna (Pao et al., 1982).
TABLE 2-10
Contribution of Animal Products to Mean Intake of Fat and Percentage of Fat Based on 1-Day Intake.
Table 2-11 summarizes 1985 CSFII data on the fat and cholesterol in women's diets. The red meat, poultry, and fish group (including mixtures) was the primary source of fat, fatty acids, and cholesterol in women's diets, with red meat providing about half of these components. Red meat was the most significant source of cholesterol, although the contribution of poultry was only slightly less than that of beef or other red meats. Shell eggs accounted for only 29 percent of total cholesterol intake because most eggs are consumed as ingredients in other foods, so that the cholesterol originating from eggs is distributed among other food groups such as grain products.
TABLE 2-11
Percentage of Fat, Fatty Acids, and Cholesterol in Diets of Women, Ages 19-50 Years Based on 1-Day Intake.
The USDA is developing an automated system for classifying ingredients of mixtures reported in its surveys into appropriate groups. For example, the beef and vegetables in beef stew now classified as a mixture will be moved to the beef and vegetable groups. This classification system will be used to supplement the system now used, not replace it. The partly completed system was used to determine the proportion of fat and cholesterol in the 4-day diets of women surveyed in 1985. Commercially prepared bakery products such as bread, doughnuts, and snacks have not yet been separated into ingredients and some ingredients are in raw form.
Preliminary results suggest that the red meat, poultry, and fish category provided about one-fourth of the fat and more than one-third of the cholesterol. Fresh, unprocessed red meat provided almost one-fifth of the total fat and cholesterol. Eggs provided more than 40 percent of the cholesterol. Fats and oils provided about one-tenth of the fat, one-tenth of saturated fatty acids, and only 5 percent of the cholesterol, all of which was from animal sources. This information is summarized in Table 2-12.
TABLE 2-12
Estimated Percentage of Contribution of Fat, Saturated Fatty Acids, and Cholesterol by Animal Products in Diets of Women, Ages 19-50 Years.
Vitamins
Animal products contribute between 33 and 100 percent of available quantities of specific vitamins in the food supply. They are good sources of most of the B vitamins, particularly riboflavin, niacin, vitamin B6, and vitamin B12.
In the 1977-1978 NFCS, milk and milk products contributed 14 percent of calories but larger proportions of several nutrients. They were the primary source of riboflavin and vitamin B12 in the diet, contributing an average of nearly 30 percent. Milk and milk products also contributed over 16 percent of vitamin A and smaller percentages of other vitamins. Eggs contributed over 4 percent of vitamin A and riboflavin.
Table 2-13 summarizes the contribution of animal products to the vitamin content of the diet, using data from the 1977-1978 NFCS. The category of red meat, poultry, and fish is the major source of the preformed niacin (44.3 percent), vitamin B6 (39.9 percent), riboflavin (24.2 percent), thiamine (23.6 percent), and vitamin A (12 percent) in the diet.
TABLE 2-13
Contribution of Animal Products to Selected Vitamins and Minerals in the Diet Based on 3-Day Intake (in percent).
Minerals
Animal products also contribute substantially to the mineral content of the food supply, as indicated in Table 2-1, providing 42 percent of the iron, more than a third of all magnesium, and over 60 percent of the calcium and phosphorus.
Iron
Prior to 1979, the red meat, poultry, and fish group was the primary source of iron in the food supply. Increased fortification of foods with iron (for example, in flour) and the decline in red meat consumption, however, have made grain products (composed entirely of nonhemoglobin iron) the primary iron source in the diet. Animal products contribute about 28 percent of the total iron to the food supply; cereals and grains account for 39.3 percent; fruits and vegetables, 19.2 percent; and dry beans, peas, nuts, and all others, 13.7 percent.
Data from the 1977-1978 NFCS indicate that animal products contribute about 42 percent of the total iron to the diet (Table 2-14). Of this amount, the red meat, poultry, and fish category provides the highest percentage, 34.5, with milk and milk products and eggs each contributing about 4 percent.
TABLE 2-14
Contribution of Animal Products to Iron in the Diet Based on 3-Day Intake (in percent).
Calcium
Animal products contribute more than 80 percent of the total calcium available in the food supply (Table 2-1). Milk and milk products provide 76.2 percent; fruits and vegetables, 8.8 percent; red meat, poultry, and fish, 4.2 percent; cereals and grains, 3.6 percent; beans, peas, and nuts, 3.1 percent; and other foods, 2.4 percent. The level of calcium in the food supply and the contribution from dairy products has remained fairly constant during the last 20 years. Despite significant declines in the consumption of fluid milk, milk is still the primary source of calcium, contributing 28 percent to the total calcium derived from dairy products; cheese is a close second at 27 percent. If current consumption trends continue, both cheese and low-fat milk should surpass whole milk as the main source of calcium in the food supply within the next year.
A number of factors influence the absorption and utilization of dietary calcium. Vitamin D facilitates the movement of calcium into the duodenal mucosal cells and increases absorption. High-protein diets also increase calcium absorption because of the action of specific amino acids, especially serine, arginine, and lysine. The presence of lactose (the carbohydrate found exclusively in animal products) and/or acidophilic flora (such as lactobacilli in cultured dairy products) also increases calcium absorption.
Substances that form insoluble complexes with calcium hinder its normal absorption; these include phytates (found in the outer layers of cereal grains), oxalates (present in spinach, Swiss chard, beet tops, cocoa, and rhubarb), and free fatty acids. Foods high in saturated fatty acids are likely to produce free fatty acids that will then combine with calcium to form insoluble complexes.
Data from the 1977-1978 NFCS indicate that animal products contribute about 60.7 percent of the total calcium in the diet (Table 2-15). Of this amount, the milk and milk products category, provides 50.4 percent and the meats and eggs categories contribute 7.5 and 2.8 percent, respectively. Grain products provide 22 percent, some of which is provided by ingredients from animal sources such as milk and eggs.
TABLE 2-15
Contribution of Animal Products to Calcium in the Diet Based on 3-Day Intake (in percent).
Trends in Individual Commodities
Red Meat, Poultry, and Fish
Food Supply Data (1965-1985)
In 1985 the total food supply of red meat, poultry, and fish was at an all-time high of 185 pounds per capita, edible weight (Table 2-16)—a 15 percent increase over 1965 and an 8 percent increase over 1975. This edible weight series is new from the USDA as of 1985. Data on fish, which is reported by the U.S. Department of Commerce, have always been reported on an edible weight basis, but a comparable series was not available for red meat and poultry. The purpose of reporting the data on an edible weight basis is to facilitate quantity comparisons between types of meat. The edible weight measure excludes all bones but does include the 0.25 to 0.5 inch of separable fat normally sold on retail cuts of red meat. The trends for individual commodities, though, have differed greatly, with changes in different directions and of different magnitudes.
TABLE 2-16
Per Capita Disappearance of Red Meat, Poultry, and Fish by Edible Weight (in pounds).
The largest increase in per capita disappearance has been for poultry; between 1965 and 1985, chicken increased 72 percent and turkey increased 69, percent. From 1980 to 1985, total poultry increased more than 13 percent; from 1975 to 1985, it rose more than 40 percent.
In 1985 per capita disappearance of red meat was about .7 percent higher than it was in 1965, but it has dropped about 2.5 percent since 1975 and about 2 percent since 1980. Per capita disappearance of red meat has decreased more than 10 percent from its highest level of 135.3 pounds in 1971 to its 1985 level of 121.4 pounds.
Beef accounts for more than 60 percent of the four items (beef, veal, lamb, and pork) in the red meat category. In 1985 per capita disappearance was up about 7 percent compared to 20 years ago (74.4 pounds in 1985 versus 69.5 pounds in 1965). Per capita disappearance of beef peaked in 1976, at 89.0 pounds. Both veal and lamb, which together make up a little over 2 percent of total red meat, have remained stable over the past 10 years at about 1.5 pounds per capita, although they are both at less than half their 1965 levels.
Per capita disappearance of pork has fluctuated considerably during the past 15 years, from a high of 52.7 pounds in 1971 to a low of 37.1 pounds in 1975. In 1985, it was 44.2 pounds. At present, pork accounts for more than a third of the total red meat in the food supply.
Fish in the food supply was at a record high of 14.5 pounds per capita in 1985, up nearly 19 percent since 1975 and 34 percent since 1965.
A number of theories attempt to explain these trends. Short-term reactions to situations such as shifts in consumer price relationships owing to increased supplies of one commodity relative to another may account for some changes. Other, longer term factors, such as diet and health concerns, might also play an important role (Stucker and Parham, 1984).
Although the food supply data do not directly measure food intake, they have been used to estimate the amount of food potentially available on a cooked, edible basis. The 185 pounds of red meat, poultry, and fish available per capita in 1985 translates to roughly 8.1 ounces per day, raw weight. The USDA estimates that cooking losses for meat, poultry, and fish range from 15 to 30 percent, depending on the type of commodity and the method of preparation (U.S. Department of Agriculture, 1975). Using this adjustment for the conversion of the data indicates that roughly 5.7 to 7.0 ounces of cooked, edible red meat, poultry, and fish were available from the food supply per person per day in 1985. Spoilage, plate waste, and trimming during preparation further reduced the amount actually ingested. Also, this estimate does not take into account differences in intake by age and sex groups or variations that occur in daily intake.
Dietary Survey Data
In general, the dietary survey data reflect the decline in red meat consumption indicated by the food supply data (Table 2-17). Comparison of data from the 1977-1978 NFCS and the 1985 CSFII indicates that the average daily intake of beef by women ages 19 to 50 declined by 45 percent compared with 22 percent for pork and 19 percent for processed meats. In contrast to the food supply data, the survey of women's diets indicated a 14 percent decline in chicken intake. Comparison of data from the 1977-1978 NFCS and 1985 CSFII indicate that the intake of fish increased 18 percent.
TABLE 2-17
Meat, Poultry, and Fish: Trends in Consumption and Mean Intake.
Despite significant declines in the intake of red meat by women between 1977 and 1985, intake of the total red meat, poultry, and fish category declined only slightly. Mixtures accounted for half of the total intake of the red meat, poultry, and fish category in 1985, compared with one-third in 1977. The shift to mixtures signifies that meats are being used more as an ingredient in meals and less as a separate menu item.
The 1985 CSFII data indicate that changes in men's intake of meat were similar to those for women. Mixtures that may have included foods other than meats (such as grains) accounted for two-thirds of the total intake of red meat, poultry, and fish.
National Live Stock & Meat Board Study
The National Live Stock & Meat Board study, ''Contribution of Red Meat to the U.S. Diet'' (Breidenstein and Williams, 1987), estimated meat intake using per capita disappearance data and private survey data (Yankelovich, Skelly and White, Inc., 1985). The private survey segmented the population into different user levels (light, moderate, or heavy) on the basis of telephone interviews of 1,211 individuals identified as the primary food shopper for the household. This analysis differs from recall data from dietary, surveys in that estimates for "ingested" and "available" red meats are reconciled numerically. The surveyors estimated that daily per capita cooked red meat intake for light users was 41.4 grams (1.45 ounces); for moderate users, 117 grams (4.14 ounces); and for heavy users, 216.31 grams (7.66 ounces). The estimated breakdown by different types of meat is given in Table 2-18. The nutrient contribution of red meat by use level is summarized in Table 2-19. The committee believes that the data provide a useful analysis of red meat consumption in the United States.
TABLE 2-18
Estimated Average Daily Consumption of Cooked Red Meats in the U.S. Diet, 1984.
TABLE 2-19
Nutrient Contribution of Total Cooked Red Meat Ingestion by Consumption Level in the U.S. Diet, 1984.
Milk, Milk Products, and Eggs
Food Supply Data (1965-1985)
Historically, milk and milk products have been an important part of the U.S. diet. But as for red meats, trends for individual milk and milk products differ greatly (Table 2-20): low-fat milk, yogurt, and hard cheese have increased the most of all products in this category from 1965 to 1985, whereas whole and processed milk (condensed and evaporated) have shown the largest decrease during the same period.
TABLE 2-20
Per Capita Trends for Selected Milk, Milk Products, and Eggs.
Whole, low-fat, skim and flavored milks and buttermilk currently constitute nearly three-fourths of the milk and milk products group on a product weight basis. In 1985 per capita sales of fluid whole milk was at about half the level it was in 1965 (116.5 pounds versus 236.5 pounds). In contrast, per capita sales of low-fat milk increased more than 680 percent during this same period, from 10.9 pounds in 1965 to 85.0 pounds in 1985. This dramatic shift from whole milk to low-fat milk is most likely due to a combination of health concerns and taste preferences, since the per capita sales of skim milk have remained at about the same level for two decades. Bunch (1985) suggests that the food supply of fluid milk has declined due to demographic changes and competition from other beverages.
Yogurt is another dairy product that has increased tremendously in the food supply, particularly during the past 10 years. Between 1980 and 1985 it increased over 50 percent, between 1975 and 1985 it increased more than 90 percent, and between 1965 and 1985 it increased more than 1,200 percent. Nevertheless, per capita sales of yogurt account for little more than 1 percent of all dairy products. The amount of hard cheese in the food supply has also increased, by over 27 percent since 1980, by 9.5 percent between 1970 and 1985, and by more than 130 percent between 1965 and 1985. Ice cream, cottage cheese, and butter have remained around their 1970 levels.
Dietary Survey Data
NFCS (1977-1978). The percentage of individuals using fluid milk decreased abruptly for those in their late teens and early twenties. Whereas 94 percent of males and 89 percent of females ages 15 to 18 drank milk at least once during the 3 survey days, only 78 percent of the males and 79 percent of the females ages 23 to 34 reported consuming milk. Average intake and serving size also dropped abruptly after age 18. Milk consumption for males was highest for 12-to 18-year-olds, who consumed an average of 19 ounces a day.
Women ages 35 to 50 drank the least amount of milk in the survey, averaging only 5 ounces per day. Twenty-eight percent of the women in this age group had not drunk milk on any of the 3 survey days. Males drank more milk than females in every age group.
Fifty-four percent of the survey respondents consumed eggs on at least 1 of the 3 survey days (Table 2-21). (Data are for eggs that are reported as a separate food and do not include quantities eaten as an ingredient in other foods.) In general, males had slightly higher intakes than females, averaging 37 grams per day compared to 24 grams for females. One large egg weighs approximately 50 grams. The survey data indicate that older adults eat eggs more frequently than do younger adults, although the intake per user is not as high. Twenty-four percent of males and 13 percent of females ages 65 and older ate eggs on all 3 of the survey days, compared with only 10 percent of the total population.
TABLE 2-21
Intake of Eggs.
CSFII (1985). Women's intake of milk as a beverage and in dairy products has remained relatively constant between 1977 and 1985 (Table 2-22). The changes within the dairy category parallel those found in the food supply data. Total fluid milk intake declined 5 percent, but there was a substantial shift from whole milk, which was down 35 percent, to low-fat and skim milk, which was up 60 percent. Only about half of the women had drunk milk on the day surveyed (Behlen, 1986).
TABLE 2-22
Milk, Milk Products, Eggs, Fats, and Oils: Trends in Consumption and Mean Intake.
Cheese intake was up 6 percent from 1977 to 1985. This is much less of an increase than that indicated by the food supply data. However, a large proportion of cheese is consumed as an ingredient in mixed foods such as macaroni and cheese and in pizza, and in the CSFII, these foods would be included in the grain mixtures category. Similarly, cheese served on a hamburger or in a ham and cheese sandwich would be included in the meat mixtures category. Intake of meat mixtures and grain mixtures increased significantly from the previous survey. Therefore, the smaller increase in cheese intake in the CSFII is likely associated with the fact that more meat and grain mixtures are being eaten.
Fats and Oils
Food Supply Data (1965-1985)
Quantities of fats and oils in the food supply are measured by the manufacture of products such as shortening, margarine, and salad and cooking oils (Table 2-23). Data include all fats and oils except those that occur naturally in foods such as meats, milk and milk products, and nuts. Between 1965 and 1985, per capita disappearance of fats and oils increased 32 percent. Over the same time period, there was a shift from animal to vegetable sources, although this trend seems to have leveled off (Figure 2-3).
TABLE 2-23
Per Capita Disappearance of Separated Fats and Oils (edible weight in pounds).
Figure 2-3
Total fat content of the food supply, 1985. Between 1965 and 1985 the total fat content of the food supply increased by about 34 percent. The shift from animal to vegetable sources has been even more dramatic: Fat from animal sources decreased 22 percent (more...)
About 50 percent of fats and oils are used in processed foods such as baked goods, salad dressing, and potato and corn chips. The remainder is used by restaurants and institutions or purchased in grocery stores for home use. Restaurant use of fats and oils increased 69 percent between 1969 and 1979, primarily because of the increase in the number of fast-food restaurants and other establishments serving fried foods like chicken, fish, and french fried potatoes (Bunch and Hazera, 1984). Although there is little information on changes since 1979, restaurant use of edible tallow for frying is primarily responsible for the increased use of animal fats since 1980 (Karen Bunch, USDA Economic Research Service, personal communication, 1986).
In 1985, butter, lard, and tallow accounted for 20 percent of the total use of fats and oils. About 4 pounds of lard and tallow per capita were used directly, either by restaurants or consumers. Another 6 pounds were used to produce shortening and, to a lesser extent, margarine. Similarly, a variety of vegetable oils are used in the production of fat and oil products. Vegetable oils contain varying amounts of saturated and unsaturated fats, as shown in Table 2-8. Some vegetable oils, such as coconut and palm, actually contain as large a proportion (if not larger) of saturated fatty acids as tallow and lard.
Because these data are derived from estimates of production, they do not measure actual ingestion of fats and oils. Waste may be significant, especially for salad dressings and for fats and oils used in frying. Estimates of waste range from 2 percent for table spreads such as butter and margarine to 20 percent for salad oils and frying fats (Yankelovich, Skelly and White, Inc., 1985). Some estimates of waste are as high as 30 percent for these products (U.S. Department of Agriculture, 1975).
Dietary Survey Data
NFCS (1977-1978). It is difficult to measure intake of fats and oils (such as margarine or cooking oils) through a survey of individual diets because a large proportion of this fat is used in cooking or consumed in processed foods. Therefore, reported intake levels of fats and oils will be below the amounts actually consumed.
Intake of fats and oils reported in the NFCS ranged from 8 grams/day for children ages i to 11 to 16 grams/day for adults ages 19 to 64. Adult males ages 51 to 64 had the highest intake of all age groups, 21 grams/ day. One tablespoon of butter or margarine weighs 13 grams; a tablespoon of salad oil weighs 11 grams.
CSFII. The trend in the food supply data toward increased use of fat and oil products was also reflected to some extent in food intakes measured by the CSFII. Again, these are fats and oils that are consumed directly or in processed foods rather than fats that occur naturally in foods. Women's intake of the fats and oils reported separately increased 14 percent between 1977 and 1985 because of a 38 percent increase in salad dressing use. Fats and oils consumed as ingredients in baked goods and mixed dishes, as seasoning, or absorbed during cooking are a part of the weight of the reported food. Since these amounts are expected to be substantial, surveys of individual intakes are not appropriate for measuring change in consumption of fats and oils.
Special Studies
Household Refuse Analysis Project
The Household Refuse Analysis Project at the University of Arizona attempted to estimate dietary patterns through recording label information from discarded food packages and analyzing food debris in household refuse. This project has collected data from six cities since 1977 (Rathje and Ho, 1987). Over a 7-year period from 1979 to 1985, the quantities of meat fat recorded from Tucson, Arizona, refuse indicated a trend toward greater discard of fat from meat cuts. From 1979 to 1982, the percentage of fat cut off red meats averaged between 3 and 10 percent; from 1985 to 1985 the discard percentage increased to 12 to 16 percent. Data from a retirement community in Arizona revealed that meat fat discard percentage rose from 13 percent in 1976 to 93 percent in 1985 (Rathje and Ho, 1987).
The other trend that was identified by this project is an overall decrease in the purchase of red meat with separable fat (for example, as retail cuts in the form of chops, steaks, and roasts) and an increase in the purchase of red meat with nonseparable fat (for example, ground beef, sausages, luncheon meats, hot dogs, and bacon). Convenience is cited as the most likely explanation for these seemingly contradictory trends; another possibility is that many consumers may not realize that the levels of fat present in ground beef, sausage, hot dogs, and bacon are substantially higher than those in closely trimmed retail cuts (Rathje and Ho, 1987).
St. Joseph's University/American Meat Institute Study
Another estimate of the contribution of the fat present in red meat to the total fat content in the diet was made in a study for the American Meat Institute by the Academy of Food Marketing at St. Joseph's University (Stanton, 1987). Researchers substituted new nutrient composition data from USDA Agriculture Handbook No. 8-13 for beef (U.S. Department of Agriculture, 1986) and USDA Agriculture Handbook No. 8-10 for pork (U.S. Department of Agriculture, 1983) for the nutrient intake data from the 1977-1978 NFCS, made adjustments for the change in retail beef trim from 0.5 to 0.25 inch, and reestimated the number of individuals consuming the separable fat on meat. These adjustments resulted in an average total fat intake of 28 to 34 grams for males age 18 and older and 21 to 24 grams for females age 18 and older. The analysis indicated that with adjustments for these three factors, for males age 18 and older, there was a reduction in total fat intake of 11 to 12 percent and a reduction in grams of fat from meat of 28 to 29 percent; the reductions from previously reported NFCS estimates of fat consumption were comparable for females of the same ages.
National Live Stock & Meat Board Study
The National Live Stock & Meat Board study (Breidenstein and Williams, 1987), which used per capita disappearance data and private consumer survey information, estimated the nutrient contribution of red meat to the diets of light, moderate, and heavy users of red meat. Researchers estimated that for moderate users, red meat contributes less than 12 percent of the calories from fat, of which about 4.5 percent is from saturated fat. In addition, red meat accounted for about 92 mg of the cholesterol and 526 mg of the sodium per day in the diets of moderate users. A summary of the study's findings is presented in Tables 2-18 and 2-19.
