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OCR for page 24
H. N. MUNRO
Health-Related Aspects
of Animal Products
for Human Consumption
I N T RODU CT I ON
The human race is dependent on a supply of foods that resects two
aspects in the development of man, aspects that are quite dissimilar
in time scale. First, man has inherited requirements for nutrients that
date back to the earliest animal cells, which emerged about 1 billion
years ago (Munro, 19691. An examination of the nutrient needs of
animal cells from single-celled protozoa through insects, fish, birds,
and mammals, including man shows a strong qualitative similarity
in requirements. From the constancy of this pattern, it can be concluded
that the earliest animal cells must have eliminated the DNA correspond-
ing to biosynthetic pathways for certain amino acids (the essential amino
acids) and the B-complex vitamins. In this way, animal cells all became
dependent on an outside source of complex organic nutrients: food.
Man emerged some 2 million years ago, probably in central Africa, and
spread slowly northward, arriving at the Mediterranean basin and the
countries of the Middle East about half a million years ago.
The second aspect was the development of agriculture and the do-
mestication of animals, which took place in the Near East about 10,000
years ago-that is, only about 300 generations back. Radiocarbon
dating shows that domestic cattle, pigs, and sheep were first raised in
this area about 8000 B.C., when cereals also appear to have been
cultivated for the first time. During the preceding 2 million years, man
was a hunter and a gatherer, as shown in many parts of the world by
cave paintings, carvings, and remains of food animals. Examination of
24
OCR for page 25
Health-Related Aspects of Animal Products
25
people in modern hunter-gatherer communities shows that they have
low blood pressures and low blood cholesterol values.
We do not know how much the change in life-style toward de-
pendence on crops and domesticated animals had to do with the
emergence of degenerative diseases. It did, however, allow rapid growth
of the world population. One final event completed the revolution.
Shortly after the time of these agricultural developments in the Near
East, a tribe living north of the Black Sea and speaking a primitive
Indo-European language succeeded in domesticating the horse and took
over the farming communities to the south. With its new means of
locomotion and knowledge of agriculture, this Indo-European popula-
tion spread during the last 4,000 years from India in the East to all of
Europe in the West and by later exploration to North and South
America and Australasia, giving rise to some 40 languages derived from
the original Indo-European tongue (Barker, 19721. Thus, mobility
resulted in the rapid spread of agricultural techniques capable of sustain-
ing large populations.
The history of recent developments in population growth and food
supplies is well known. A survey by Thompson (1972) compares in-
creases in population with increases in world production of cereal
grains and red meat from 1950 through 1970. Cereal output roughly
paralleled population increase up to 1965; during the next 5 years,
output per capita increased. On the other hand, red meat production
rose much more rapidly than population over the 20-year period,
averaging 36 lb per capita per year in 1950 and 48 lb in 1970. The
largest part of this gain occurred between 1950 and 1960.
~ . ,
RECENT TRENDS IN CONSUMPTION OF ANIMAL AND PLANT
FOODS IN THE UNITED STATES
Most of our information about patterns of food consumption in the
United States comes from two sources. First, the U.S. Department of
Agriculture (USDA) makes periodic surveys of the quantities of food-
stufis sold for civilian consumption. Friend (1967) has summarized
these data and has also computed the intakes of nutrients obtained from
these various foods at different times during the period 1909-1965.
Second, the USDA has also conducted household food-consumption sur-
veys that provide information about the actual amounts of foods con-
sumed by individuals (Agricultural Research Service, 1969~.
Figures 1 and 2 show annual consumption per capita of various
classes of foodstuffs sold to the U.S. public during the period 1909-
1965. Figure 1 shows that the annual intake of all meats was almost as
OCR for page 26
26
250
200
: _
Meat ~ Ibs)
150
103 ~5
o
100
50
o
1 = 1909-13
2= 1925-29
3=1935-39
4= 1 947-49
5- 1957-59
6= 1 965
6
H. N. MUNRO
Dairy Products
(quarts)
~ //
/ //
/ //
4 5 6
/ / /
7
2
7
Poultry & Fis
_
/
htibs, Eggs (lbs]
/
7
~2 _
6
FIGURE 1 Annual U.S. consumption per capita of foods of
animal origin over the period 1909-1965. The figures are for
retail-weight equivalents. (Drawn from data compiled by
Friend, 1967. )
OCR for page 27
Health-Related Aspects of Animal Products
250
200
1 50
100
50
o
100
~ _
, __
2
3
Flour ~
Cereals (Ibs)
Potatoes (Ibs) / /
/ /
_
-
1
1 = 1909-13
2= 1925-29
3= 1935-39
4= 1947-49
5 = 1 957- 59
6= 1965
Fruit (Ibs)
. /
3
Sugar (lids)
| Fats ~ Oils(lbs)
50~ (Butter in black) ~
FIGURE 2 Annual U.S. consumption per capita of foods of plant origin, to-
gether with fats and oils of mixed origins, over the period 1909-1965. The figures
are for retail-weight equivalents. (Drawn from data compiled by Friend, 1967.)
high in 1909 ( 141 lb per capita per year) as in 1965 ( 148 lb per capita)
equivalent to about 180 g of meat per capita per day. However, this
constancy obscures a change in type of meat; the proportion of meat
consumed as beef shows a steady rise during this 60-year period. It will
also be seen that the meat intake showed a temporary reduction
OCR for page 28
28
H. N. MUNRO
during the depression years of the late 1920's and 1930's. But poultry
and fish did not reflect this drop in intake, and after 1947 intake rose
sharply for poultry. Dairy products showed a steady gain during the
period 1909-1949 but more recently have remained at a plateau level of
intake. Intake of eggs showed no consistent trend in the period surveyed.
Figure 2 gives a corresponding picture for foods of plant origin. A
striking change in consumption habits is shown by the progressive re-
duction in intake of potatoes, hours, and cereals, with a consequent
fall in carbohydrate intake as starch. But intake of sugar has been
stable at an annual rate of 110-120 lb per capita since before 1925;
thus, in recent years intake of sugar has provided a larger proportion
of the diminishing total intake of carbohydrate. Although the total
consumption of fats and oils remained constant over the period, this
conceals a steady and considerable reduction in butter intake and its
replacement by vegetable fats and oils, especially since 1947. Fruits
and vegetables displayed an increased availability per capita until the
1940's, when there was a decline in per capita consumption. In view
of the increase in availability of dairy products and poultry, and the
reduction in potatoes and flour during the period 1903-1965, it is not
surprising that the proportion of energy intake from carbohydrate fell
from 56% to 47% over these six decades and that fat intake rose
from 32% to 41% (Table 11. Protein was constant at 11%-12%.
In addition to nutrient calculations based on the use of foods by the
U.S. civilian population, we have data based on direct household con-
sumption surveys made in 1965 (Agricultural Research Service, 1969~.
Table 2 shows the sources of energy in the diets of males studied in this
survey. It is evident that 15%-16% of total energy intake comes from
dietary protein-about 45% from fat and 40% from carbohydrate.
This picture confirms the high proportion of energy derived from fat
TABLE 1 Energy Available per Capita per Day from the U. S. Food
Supply, 1909-1965 a
Total Percentage of Energy
Energy
Year (kcal/day) Protein Carbohydrate Fat
1909-1913 3,490 12 56 32
1925-1929 3,470 11 54 35
1935-1939 3,270 11 53 36
1947-1949 3,230 12 49 39
1957-1959 3,140 12 47 41
1965 3,160 12 47 41
a SOURCE: Friend (1967).
OCR for page 29
Health-Related Aspects of Animal Products
29
TABLE 2 Sources of Energy in the Diets of Males of Different Ages
Computed from Household Surveys in 1965a
Age Percentage of Energy
Group
(years ) Protein Carbohydrate Fat
12-14 15 43 43
18-19 1 6 41 44
35-54 16 37 45
65-74 16 39 44
SOURCE: Leveille ( 1975 ) .
(Table 1~. Table 2 also shows that with increasing age there is a
tendency for a smaller proportion of total energy to be derived from
carbohydrate sources. More striking is the high proportion of energy
from fat sources throughout life.
We can now ask whether the average U.S. diet, as it has evolved to
the present, provides adequate amounts of all nutrients, and what each
group of foodstuffs has contributed to the pattern of nutrient supply.
Leveille ~ 1975 ~ has made an interesting comparison between the
intakes of various nutrients at different ages, as evaluated by the 1965
household food-consumption survey (Agricultural Research Service,
1969), and the requirements for these nutrients given in the 1974 edi-
tion of Recommended Dietary Allowances (NRC, 19741. Table 3 sug-
gests that the energy content of the diet of each age-group is about
adequate and that all groups are consuming much more protein than
they require. The average amount of calcium consumed is adequate for
males but is probably less than desirable for older women. Iron intake is
satisfactory for males but is inadequate for all groups of women except
the elderly. Intakes of vitamins are adequate except for the thiamine
intake of older women. The low thiamine intake of older women may
not be significant; their total energy intake is low, and thus metabolic
demands on the supply of thiamine are reduced.
From this survey of food and nutrient patterns in the United States,
it is apparent that we should consider the role of animal foods in relation
to those nutrients that are likely to be either in excess (fat, protein)
or in deficiency (calcium, iron) .
SIGNIFICANCE OF ANIMAL SOURCES OF FAT
The progressively higher content of fat in the U.S. diet has often been
condemned as a leading cause of atherosclerosis. This conclusion is
OCR for page 30
30
H. N. MUNRO
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OCR for page 31
Health-Related Aspects of Animal Products
31
based on evaluation of cholesterol levels in the blood. Attempts have
accordingly been made to reduce intake of total fat, in particular by
replacing saturated fats with polyunsaturated fats of vegetable origin.
To this can be added the admonition to reduce cholesterol intake. Pro-
grams of this kind have been advocated to stem the increasing incidence
of coronary heart disease. For example, the American Heart Association
~ 1973 ~ made the following dietary recommendations:
In most persons, but not all, the level of cholesterol and other fats in the blood
can be decreased and maintained at a lower value by conscientious and long-term
adherence to a suitable diet. In most individuals, this would entail:
( 1 ) A significantly decreased intake of saturated fat;
(2) A significantly increased intake of polyunsaturated fat, with polyunsaturated
fats being substituted for saturated fats in the diet wherever possible
(3) A decreased intake of cholesterol-containing foods;
(4) A caloric intake adjusted to achieve and maintain desirable weight.
If we accept these general conclusions, it is legitimate to ask how
extensive changes in life-style have to be in order to significantly de-
crease the chances of coronary heart disease. Since the effects of differ-
ent fats are thought to affect the incidence of coronary disease through
alterations in blood cholesterol levels, it is customary to compare the
action of fats for cholesterol-lowering action. For example, Vergroesen
(1972) compared the changes in serum cholesterol content of varying
fat mixtures fed to volunteers receiving 40% of their energy intake
as fat. These fat mixtures provided 10% palmitic and stearic acids,
14% oleic acid, and 76% linoleic acid. Over a 4-week period, there was
a 20% reduction below the initial cholesterol level. When half of the
linoleic acid was replaced by oleic acid, the fall in cholesterol level was
only 10%; there was no reduction when half of the linoleic acid was
replaced by elaidic, lauric, or myristic acid. Although there is no general
agreement regarding quantitation of the effects of various combinations
of fatty acids on serum cholesterol content, the above data emphasize
the need for the polyunsaturates to predominate in order to achieve an
extensive reduction. This is reflected in the "Keys equation" (Keys et al.,
1959; Anderson et al., 1961), in which the change in the cholesterol
content of serum in milligrams per 100 milliliters resulting from an
alteration in dietary fat composition can be predicted to be 2.68 times
the change in saturated fat (percentage of total calories) minus 1.23
times the change in polyunsaturated fat (percentage of total calories).
Thus, in order to prevent an elevation in serum cholesterol level, the
equation requires two thirds of the dietary fat to be taken as poly-
unsaturates. A more detailed but essentially compatible equation is
provided by Hegsted et al. ~ 1965 ~ .
OCR for page 32
32
H. N. MUNRO
The role of the ratio of polyunsaturates to saturated fatty acids is
confirmed in long-term studies on controlled populations (Turpeinen
et al., 1968; Dayton et al., 1969; McGandy et al., 19721. In the study
of Turpeinen et al. (1968), for example, the diet of patients at one
mental hospital was changed for a 6-year period while a second hospital
served as control. Then the roles of the two hospitals were switched
for a further 6 years. In the control diet, the ratio of polyunsaturated
to saturated fatty acids was about 0.2:1, whereas the experimental diet
provided a ratio of about 1.5:1; the latter diet also provided somewhat
less cholesterol. During the first period, serum cholesterol levels fell
about 50 mg per 100 ml on the experimental diet; during the second
(reversal) phase, the difference between experimental and control
groups was about 30 mg per 100 ml. The incidence of coronary heart
disease in the group on the experimental diet was half that of the
group on the control diet (Karvonen, 19721.
In order to achieve such effects, extensive changes in eating habits
are required, and these demand considerable self-discipline. In the
New York Anti-Coronary Club trial of prevention (Christakis et al.,
1966a,b), beef, mutton, and pork were restricted to four meals a week;
poultry and veal were eaten four or five times a week; and fish was
eaten at least four times a week. Margarine rich in polyunsaturates and
vegetable oils was emphasized, ice cream and cheese were avoided, and
whole milk was replaced by skim milk.
Against this background of experimental evidence, we can consider
the current American intake of fat. An examination of the trends in
fat intakes between 1909 and 1965 (Table 4) shows that the increase
in dietary fat during this period has come entirely front an increased
consumption of vegetable fats. There was a considerable reduction in
consumption of visible animal fats (butter, lard) during the period,
whereas margarine and cooking and salad oils increased. This trend
is confirmed by data on the percentage of dietary fat from different
sourcesin the years 1959andl967 (Food Fats and Oils, 19681.This
compilation (Table 5) shows a reduction in visible fats of animal origin
and an increase from vegetable sources over the 8-year interval. Table 6
indicates the degree of saturation of the dietary fat during the period
1909-1965. Intake of saturated fatty acids was constant during this
period; there was a slight rise in oleic acid (monounsaturated) intake
and nearly a doubling in consumption of the polyunsaturated essential
fatty acid, linoleic acid. In relation to total energy intake, linoleic acid
intake increased from 2.7% of total caloric intake in 1909-1913 to
5.4~o in 1965, whereas saturated fatty acids accounted for 15.2%.
If we apply the Keys equation to the 1965 diet, we are presented with a
OCR for page 33
Health-Related Aspects of Animal Products
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OCR for page 34
34
H. N. MUNRO
TABLE 5 Proportion of Total Daily Fat Intake Derived from Visible
and Invisible Animal and Vegetable Fats a
Percentage of Total Fat Intake
Group of Fats 1959 h 1967 c
Animal
Visible ~12.8 8.2
Invisible e 54.1 51.7
Total 66.9 59.9
Vegetable
Visible f 26.1 32.9
Invisible ~7.1 7.4
Total 33.2 40.3
a Derived from Food Fats and Oils (1968).
b Total daily fat intake per capita, 146 g.
c Total daily fat intake per capita, 148 g.
d Butter and lard.
e Dairy products, eggs, meat, poultry, fish.
~ Margarine, cooking and salad oils, shortening.
g Beans, peas, soya, vegetables, grains.
gross excess of saturated fatty acids, and in consequence the diet would
be expected to raise serum cholesterol levels by 34 mg per 100 ml of
serum. Much of this rise can be attributed to the saturated fats of meat
products. This emphasis on fat derived from meat, poultry, and fish
increases with age (Table 7) and must therefore contribute to the pro-
gressive elevation of cholesterol level. As the U.S. male grows older,
a greater proportion of dietary fat comes from meat, poultry, fish, and
eggs and less from milk and milk products, grains, and legumes.
It should be pointed out that coronary heart disease is not uniquely
determined by intake of saturated fat and cholesterol. It has been
TABLE 6 Trends in Fatty Acids Available per Capita per Daya
Fatty Acids (g per day)
Total Oleic Linoleic
Year Saturated Acid Acid
1909-1913 50 52 11
1925-1929 53 55 13
1935-1939 53 55 13
1947-1949 54 58 15
1957-1959 55 58 17
1965 54 59 19
a SOURCE: Friend (1967).
OCR for page 35
Health-Related Aspects of Animal Products
35
TABLE 7 Sources of Dietary Fat in the Diet of U.S. Males in 1965 a
Age Group ( % )
Fat Source
12-14 18-19 35-54 65-74
Meat, poultry, fish33 37 44 41
Milk products21 18 12 13
Eggs4 44 6 8
Fats and oils13 13 15 15
Grains and legumes21 19 16 16
Fruits and vegetables6 7 7 7
~ Derived from Agricultural Research Service (1969) by Leveille ( 1975).
claimed that sucrose and the softness or hardness of the local water
supply are important dietary factors. Factors associated with life-style
are also determinants, as shown by the comparison between brothers in
Ireland and Boston (Brown et al., 19701. This study shows that the
Irish residents consumed more energy, total fat, and animal fat, yet they
had half the incidence of coronary disease. Lees and Wilson (1971)
summarized the evidence showing that high blood-lipid levels fall into
at least five constitutional (hereditary) classes, two of which (Types II
and IV) are common and react differently to diet. Type II patients
show an increase in blood lipids in response to saturated fats, whereas
Type IV carry an excess of blood lipids formed endogenously from
dietary carbohydrate and thus respond to the carbohydrate content of
the diet.
SIGNIFICANCE OF PROTEIN INTAKE FROM ANIMAL FOODS
It has already been shown (Table 3) that the intake of protein at all
ages from 12 years upwards is considerably in excess of the recom
TABLE 8 Dietary Protein Intake of U.S. Males of Various Ages a
Recom- RDA
· mended Met from
Protein Consumption
Dietary Animal
Age Total Animal Plant Allowance Protein
(years) (g/day) (% ) (do ) (g) (% )
12-14 100 70 30 44 159
18-19 118 73 27 54 160
35-54 106 74 26 56 140
67-74 82 74 26 56 108
a Derived from Agricultural Research Service ( 1969 ) by Leveille ( 1975 ) .
OCR for page 36
36
H. N. MUNRO
mended dietary allowances (RDA). Table 8 provides estimates of actual
intakes for males of different ages. Before the age of 55, daily intake
exceeds 100 g, and drops only in the later years, a phenomenon noted in
earlier data from Scotland (Munro, 19641. At all ages, animal sources
provide nearly three-fourths of the total protein intake, and this alone
ensures much more than the ADA at all ages. Examination of estimated
protein intakes per capita during the past 60 years (Table 9) shows
that total dietary protein content has not changed. However, this con-
ceals a shift toward animal protein and away from protein of plant
origin, because of progressively greater availability of poultry and dairy
products (Figure 1) but diminishing consumption of potatoes, four,
and other cereal products (Figure 2~.
The overabundance of high-quality protein in the present U.S. diet is
also emphasized by analysis of the daily intake of essential amino acids,
shown in Table 10 in comparison with daily needs of the same amino
acids by an adult. The requirements of adults are low (Munro, 1972),
and in consequence the amount of essential amino acids in the average
U.S. diet is several times greater than the amount required.
ANIMAL FOODS AND MINERAL REQUIREMENTS
As pointed out earlier (Table 3), the household survey of 1965 shows
that intakes of calcium and iron by women tend to be below recom-
mendations. The role of animal products in supplying these minerals
and zinc will now be considered. Table 11 shows the amounts per capita
of some minerals provided by the U.S. diet between 1909 and 1965.
The problem of meeting iron requirements exerts a perennial fasci-
nation, probably because it is the commonest deficiency in Western
countries (Ten-State Nutrition Survey, 1968-1970) and because cor
TABLE 9 Protein Available per Capita per Day in the United States
Total Sources ( % )
Protein
Year (g) Animal Vegetable
1909-1913 102 52 48
1925-1929 95 55 45
1935-1939 90 56 44
1947-1949 95 64 36
1957-1959 95 67 33
1965 96 68 32
a Derived from Friend (1967) .
OCR for page 37
Health-Related Aspects of Animal Products
37
TABLE 10 Average Daily Consumption of Essential Amino Acids in
the United States Compared with the Estimated Requirements of a
70-kg Adult
U.S. Intake Adult Requirement
Amino per Capita'' per Capita
Acid (g/day) (g/day)
Isoleucine 5.3 0.7
Leucine 8.2 0.9
Lysine 6.7 0.7
Methionine 2.1 0 9 c
Phenylalanine 4.7 1 Oc
Threonine 4.1 0.5
Tryptophan 1.2 0.2
Valine 5.7 0 9
a Data an food intake computed by Consumer and Food Economics Research Division, Agricul
tural Research Service, USDA, 1970.
b Adult requirement per capita calculated from estimated requirement per kilogram (Munro,
1972).
c Requirement for methionine includes cystine, and requirement for phenylalanine includes
tyrosine.
recting the deficiency has proved to be difficult. Consequently, major
dietary constituents must be viewed both as sources of iron and as
factors influencing iron absorption from other dietary constituents.
Animal foods serve in both capacities. The iron content of meats (Agri-
cultural Research Service, 1970) indicates that the average amount of
meats available in the diet (Figure 1)-180 g daily-should provide a
significant proportion of the total iron needed (Table 111. The second
feature of meat is its capacity to promote absorption of iron from in-
organic sources. Using dinner rolls containing radioactive-Labeled ferrous
TABLE 11 Minerals Available per Capita per Day from U.S. Foods a
Iron h Calcium Magnesium
Year (mg) (mg) (mg)
1909-1913 15.2 816 410
1925-1929 14.4 859 389
1935-1939 13.8 894 380
1947-1949 16.7 994 369
1957-1959 16.1 978 348
1965 16.5 961 340
a Derived from Friend (1967~.
b Includes iron fortification.
OCR for page 38
38
H. N. MUNRO
sulfate, Cook et al. (1973) demonstrated that fasting subjects absorbed
6.3% of the dose and a similar amount when the roll was consumed
in a meal containing meat. However, in a meal without meat, absorption
fell to 2.1%. There appears to be no evidence regarding the amount
of meat needed to achieve optimum stimulation of iron absorption.
Any reduction in meat intake should therefore take account of its
contribution to the iron requirements of man. First, it would be helpful
to determine the least amount of meat that provides maximal promotion
of iron absorption. Second, a possible avenue for reducing meat intake
without losing the benefit of its iron content would be to raise the iron
level of beef by appropriate treatment of the steer. We have shown
that the skeletal and cardiac muscles of rats contain two forms of the
iron-storage protein ferritin (tinder et al., 19731. Furthermore, when
we injected iron dextran into the rats over a 7-day period, both forms
of cardiac muscle ferritin doubled in amount and other (unidentified)
forms of iron were deposited in the muscle cells (Table 121. Thus,
if total beef intake is to be reduced, iron enrichment of beef as a means
of maintaining or even improving the iron status of the population is
worth considering.
In addition to being a significant source of iron, meat is a major
contributor to our daily intake of zinc. The average zinc intake of
adults is about 12 mg per day (Halsted et al., 1974), which tends to
fall below the recommended allowance for safety, which is 15 mg per
day (NRC, 19741. Thus, there is reason to regard zinc intake, like
iron intake, as marginally adequate.
Meat is a major source of dietary zinc. The following shows the
average amount of zinc in 100 g of each of the foods named: beef,
6.4 ma; chicken breast, l.1 ma; chicken leg, 2.8 ma; milk, 0.3 ma;
TABLE 12 Effect of Iron Treatment on Iron Content of Rat Muscle
(mg/100 g of Tissue) a
Total Heme Ferritin
Group Fe Fe Fe
Males
Control 8.2 8.9 0.3
Iron-treated 21.3 10.3 1.4
Females
Control 12.1 10.8 0.3
Iron-treated 23.5 13.3 1.8
a sOuRcE: Binder e' a!. ( 1973 ) ~
OCR for page 39
Health-Related Aspects of Animal Products
39
white bread, 0.6 ma; potatoes, 0.3 ma. Thus, it is difficult to substitute
other foods for beef and maintain an adequate intake of zinc.
There is now evidence that protein intake affects body calcium
balance. Anand and Linksweiler (1974) studied urinary calcium excre-
tion and calcium balance during 15-day periods in male subjects re-
ceiving a diet that was constant except for the protein content, which
was varied from 47 g through 95-142 g daily. These changes caused
progressively greater urinary outputs of calcium, so that calcium bal-
ance declined from +31 mg per day at the lowest protein intake
through-58 mg to -120 mg daily at the highest protein level. Beef
is a very poor source of dietary calcium but an important source of
dietary protein. Excessive consumption of beef may result in depletion
of body calcium because of the consequent high intake of protein with-
out a compensatory increment in calcium intake. Of course, other
foods of animal origin contribute calcium, notably milk. However, as
implied in Table 7, intake of milk products declines in the older popu-
lation as meat intake increases. It may be noted that skeletal depletion
and fragility are health problems of older people.
OTHER HEALTH-RELATED ASPECTS OF ANIMAL FOODS
Many attempts have been made to relate regional variation in the
incidence of diseases to differences in dietary patterns, particularly to
intake of food of animal origin. For example, Knox (1973) correlated
the regional frequency of various major diseases in Great Britain with
the intakes of nutrients as measured by the British National Food
Survey. He observed that ischemic heart disease was inversely related
to intake of calcium and vitamin C and positively related to intake of
fat and vitamin D. Several other degenerative diseases were similarly
correlated with intakes of these nutrients, suggesting a general rela-
tionship of disease to life-style.
The problems of assessing dietary and other factors in the incidence
of disease are illustrated by studies of the incidence of colonic cancer.
This condition shows a distinct difference in geographic incidence; for
example, the frequency of colonic cancer among Hawaiian Japanese is
four times the frequency recorded in Japan (Berg et al., 19721. Pat-
terns of dietary intake have been explored in relation to colonic
cancer incidence (Berg et al., 1973; Drasar and Irving, 1973; Knox,
1973) and provide some evidence for implicating animal foods pro-
viding protein and fat. It is postulated that a diet rich in meat gives rise
to carcinogenic substances because of the action of the colonic micro-
flora on the meat residues. A local action of such carcinogens is easily
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40
H. N. MUNRO
conceivable, but it is more difficult to relate an identical relationship of
animal food intake to breast cancer (Drasar and Irving, 19731. More-
over, Leveille (1975) recently compared the incidence of colonic can-
cer in the United States over the period 1935-1965 with changes
in the intake of major food items during this period. His analysis
(Table 13) demonstrates that, although the incidence of cancer rose
steadily during this 30-year period in parallel with increasing intakes of
beef, and of the combined intakes of meat, poultry, and fish, there was
a compensatory reduction in intake of cereals and potatoes. Thus, it
would be equally appropriate to relate the incidence of colonic cancer
to lack of fiber in the diet. In general, diets rich in animal foods are
low in fiber, and a comparison of the incidence of some major Western
diseases in central Africa and other underdeveloped areas has prompted
the conclusion that dietary fiber has a protective effect against cancer,
atherosclerosis, and several other conditions (Burkitt, 1973; Trowell,
19731. Klevay ( 1974) postulates that dietary fiber lowers blood
cholesterol levels through an alteration in the relative amounts of zinc
and copper absorbed from the diet. However, direct tests of the action
of administered fiber on blood cholesterol levels have been negative
(Eastwood, 19691.
Finally, animal fats have been implicated in multiple sclerosis, a
disease of the nervous system that is notoriously difficult to study be-
cause of the long periods of unpredictable improvement. Nevertheless,
TABLE 13 Incidence of Cancer of Large Intestine in Connecticut
Males and Relationship to U.S. Dietary Changes Gab
C f Annual per Capita Consumption
Large Meat,
Intestine Poultry,
(incidence/ Beef and Fish Cereal Potatoes
Period 1~) (lb) (lb) (lb) (lb)
1935-1938 19.7 44 148 205 149
1939-1942 21.2 46 165 200 140
1943-1946 23.9 45 182 198 142
1947-1950 25.9 51 176 170 121
1950-1953 27.2 51 179 163 112
1954-1957 28.9 65 192 151 111
1958-1961 30.0 63 194 148 109
1962-1965 30.4 68 201 144 110
a SOURCE: Leveille ( 1975 ) .
~ Correlation coefficients of cancer incidence: with beef intake, +0.91; with meat, poultry, and
fish intake, +0.94; with cereal intake, - 0.97; with potato intake, - 0.97.
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Health-Related Aspects of Animal Products
41
on the basis of a 20-year study, Swank (1970) claims that this condi-
tion shows much less deterioration if the animal fat in the diet is re-
placed by vegetable fats, combined with a general reduction in fat intake.
CON C L U SION
From the preceding presentation, we can consider the contribution of
animal foods, notably beef, to the U.S. diet. Table 14 displays the
nutrient content of the average diet in 1965 and the RDA of essential
nutrients for an adult male (NRC, 19743. For comparison with these,
the table gives the nutrient content of 3 oz of choice beef sirloin, in-
cluding the fat. The average diet already provides more than adequate
amounts of protein and energy, and too much saturated fat; hence,
beef is not an important source of these nutrients and nonmeat foods
would be an adequate substitute. However, on the credit side' beef has
only a modest cholesterol content and makes a significant contribution
to the daily intakes of iron, zinc, and niacin, all of which are available
near or below requirements for some classes of the population. This
evidence suggests that meat performs a significant function as a nutrient
source but would be more nutritious if the saturated fat content could
be reduced. Leveille (1975) has further emphasized that a reduction
in fat content, from choice grade to good, is obtained by shortening the
TABLE 14 Contribution of 3 oz (85 g) of Choice Beef Sirloin to
Average U.S. Diet
Adult
Average 3 Oz Male
Nutrient Diet a Beef b RDA c
Protein (g)96 2056
Energy (kcal)3160 3302,700
Fat (g)145 27
Saturated54 13
Oleic59 12
Linoleic19 1
Cholesterol (mg)500 80
Calcium (mg)960 9800
Iron (mg)16.5 2.510
Zinc(mg)12 515
Niacin (mg)21 418
a Food availability per day in the United States in 1965 (calculated from Friend, 1967) with
added estimates for cholesterol and zinc.
b From Agricultural Research Service (1970).
c From NRC ( 1974)
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42
H. N. MUNRO
period of feeding and thus reducing the feed consumed by the steer by
20%-30~o, a considerable saving in grain intake.
These conclusions represent minimal demands on current practices
in animal husbandry. In order to cope with the much more difficult
question of the relationship between intake of animal products and the
incidence of chronic and degenerative diseases, it would be necessary
to evaluate the available data much more rigorously than can be done
in one brief review paper and to plan further targeted research. Both
are major commitments for which several panels of experts would have
to be recruited. To proceed with such plans would imply a serious
commitment to implement any recommended changes. If the evidence
of benefits from a change in animal fat is sufficiently persuasive, the
recent Australian experimental method of changing the spectrum of
beef fatty acids by feeding polyunsaturates protected against rumen
digestion to beef cattle (Cook et al., 1970) could be explored further.
This maneuver resulted in a rise in ratio of polyunsaturated to saturated
fatty acids in the body fat from 0.1: 1 to 0.9: 1. In clinical trials, feeding
this beef resulted in a lowering of plasma cholesterol levels (Nester
et al., 19731. Feasibility trials of the commercial introduction of such
beef are worth considering for the benefit of at least those in the
population who desire such a change in the proportions of dietary fatty
acid.
ACKN OW L E DGM E N T
I am grateful to Dr. G. A. Leveille for making available to me before publication
his excellent manuscript (reveille, 1975) dealing with the role of animal foods
in human nutrition.
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Representative terms from entire chapter:
heart disease
