MEAT CONSUMPTION AND HUMAN HEALTH1 R. G. BROWN

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Department of Food Science and Nutrition, University of Massachusetts, Amherst, Mass.01003. Received 20 Sept. 1981, accepted 19 Oct. 1981.

BnowN, R. G. 1982 Sci. 62: 25-34.

Meat consumption and human health. Can. J. Anrm.

Meat and meat products are excellent sources of protein for the human dietary. There are. however, concerns that consumption of meat may not be in the best interests of health. These concerns date to the nineteenth century, at which time a number of "pure-food'advocates"'equated the consumption of meat with a variety of conditions including dermatitis, arteriosclerosis, constipation, flatulence

etc. and with moral laxness. In recent years, there has been concern that consumption of meat could lead to increased intake of cholesterol and saturated fatty acids which are thought to have an adverse effect on cardiovascular health. Examination of current knowledge suggests that dietary intake of cholesterol and saturated fatty acids are not primary aetiological agents for the development of atherosclerosis. There is a suggestion in the literature that meat proteins themselves may be atherogenic. The theory is that consumption of meats that are rich in methionine leads to the development of high circulating levels of homocysteine which causes atheromatous lesions to develop. Induction of homocysteinaemta by vitamin 86 deficiency did not result in the development of atherosclerosis, however, which sheds some doubt on the theory that meat proteins are atherogenic. A review of current literature reveals that there is no concrete reason to suspect that meat consumption poses any threat to human health.

La viande et les produits canr6s constituent une excellente source de prot6ines pour l'homme quoique, de plus en plus, on s'interroge sur les effets de la viande sur la sant6. D6jir au 19" sidcle, plusieurs champions des aliments purs associaient la consommation de viande d une pl6iade d'6tats pathologiques, dermatites, asrt6rioscl6rose, constipation, flatulence, etc., sans parler de relichement des moeurs. Ces dernidres ann6es, le monde m6dical en est venu b soupgonner des effets nocifs de la viande sur le systdme cardio-vasculaire h cause du cholest6rol et des acides gras satur6s qu'elle apporte i I'organisme. Toutefois, l'6tat actuel de la science incite d penser que I'ingestion de cholest6rol et d'acides gras satur6s ne serait pas I'agent 6tiologique primaire de I'ath6roscl6rose. On a par ailleurs avanc6 que les prot6ines mOmes de la viande seraint athdrogbnes, tablant sur la th6orie selon laquelle la consommation de viande, aliment riche en m6thionine, entraine la pr6sence de fortes proportions d'homocyst6ine dans le courant sanguin, ce qui provoquerait la formation de l6sions ath6romateuses. Toutefois, la provocation d'homocyst6in6mie par carence de vitamine 86 n'a pas entrain6 le d6veloppement d'ath6roscl6rose, ce qui remet donc cette hypothdse en question. L'examen de la bibliographie courante ne donne aucune raison concrbte de soupgonner une quelconque menace li6e ir la consommation de la viande. Key words: Meat, health, heart, fat, cholesterol lPresented at the Canadian Society

Food System,

l1 Aug. 198i, St.

of Animal Science Symposium entitled the Future of Meat as a Sustainable Catharines, Ontario. 0008-3984/82/6201 -0025 $2. oo

Can. J. Animal Sci. 622 25-34 (Mar. 1982)

O 25

1982 Agricultural Institute

of

Canada

26

CANADIAN JOURNAI OF ANIMAL SCIENCE

The question of meat consumption and human health is a curious one because it suggests that consuming meat may be in-

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jurious. Reference to a standard work on Nutrition (Guthrie 1979) indicates that meat and animal products are excellent sources of high-quality protein which are able to meet human protein requirements with only modest intakes. These same products also

furnish fat-soluble vitamins, vitamin Btr, certain of the water-soluble vitamins and trace metals. While not "perfect" foods, meat and animal products do have solid place in any well-planned dietary. Societies around the world which are regarded as less well developed strive to increase both the output of their economies and their meat consumption (Brown 1974). It would be curious if those societies would

knowingly move toward a less healthful diet. Yet, the title of this paper would suggest that there is concern that meat consumption may be detrimental to human health. There are current concerns that meat and meat products may be harmful to humans. Recently, the use of nitrites, coloring substances and other additives in prepared meat products has raised health questions. Likewise, the high concentration of sodium in certain prepared meats such as bologna has caused some concern (Food and Nutrition Board. 1981). Far and away the major concern with meat consumption is the potential effect of its lipid and protein component on the incidence

of cardiovascular disorders. Any of the above subjects could occupy this entire paper. The writer chooses, however, to concentrate on two areas; the history of the health concerns surrounding meat consumption and the connection between meat consumption and cardiovascular disorders. This is not to suggest that questions surrounding the addition of nitrite, sodium, colors, etc. to meat products is not of concern. They are, however, not inherent in meat and any health concerns

arising from their use can be answered through changes in manufacturing practise.

BRIEF HISTORY OF HEALTH

CONCERNS SURROUNDING MEAT CONSUMPTION No other food elicits the emotional response that meat does. A11 social groups have certain prohibitions about aspects of its consumption. North Americans of European origin tend to avoid eating things such as rats, dogs, cats, reptiles, etc. which, in other cultures, are acceptable foods (Lowenberg et al. 1919). It is well known that followers of Islam and Judaism eschew pork whilst Upper-Caste Hindu reluse to eat cattle or any meat in some instances (Lowenberg et al. 1979). Many cultures refuse to consume their fellow human beings whilst others believe that consumption of selected human parts confers certain attributes of bravery, fecundity, longevity, intelligence, etc. In some instances, the selection of meat is a matter of convenience. In the late 1600s there was a report of Connecticut Valley Indians feasting on 27 Frenchman killed in battle. The reason given was that the Indians were

hungry (Judd 1905). Most prohibitions of Western culture concerning meats have a religious or philosophical background and these may be cloaked in a gown of health. It is commonly conceded that the antimeat movement on this continent started with Sylvester Graham, best remembered

today as the originator of the Graham Cracker which in its day was a "purifier" and a health food. His inspiration was an

Anglican Cleric named Wm. Cowherd who interpreted the Bible to indicate that killing and eating animals was forbidden. Graham was won over in Philadelphia by one of

Cowherd's missionaries named Wm. Metcalfe and Graham quickly formed the idea that the right food would save man's

soul and his health. Quickly joined to Graham's vegetarian philosophies were

temperance and dress-reform. Graham's teachings can be summarized as: meat excited vile tempers and habits; it drove men to sexual excesses and those excesses filled insane asvlums: excessive lewdness and

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BROWN

MEAT CONSUMPTION AND HUMAN HEALTH

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chicken pie were the cause of cholera. Mind you the mention of lewdness was a surefire -way to fill a lecture hall in the early nineteenth century! The vegetarian movement grew under the guise of "reform." Its chief enemy was "dyspepsia", a catchall phrase used to cover a variety

of gastric

illnesses (Deutsch 1977).

The nineteenth century with its water cures and concern for "health" saw the rise of fiber (bran) as a "miracle" food and the assumption of religious overtones by vegetarianism. The chief prophet to this Table 1. Health and moral degradation stemming

fiom the consumption of meat (nineteenth (after Tibbles l9l4)

Century)

Meat causes Aggresive behaviour Sexual excesses Gluttony

Kidney disease

"vapors"

Attqaosqlclas1s Catarrh

Obesity Dyspepsia

Hypertension

Sterility

wasting

Neurastheni

of liver"

Gout

''Stone'' " Grave1" Chronic rheumatism Skin diseases (urticaria) Psoriasi

movement was John H. Kellogg'M.D. of the Battle Creek Sanitarium. Consumption of meat was considered to be the origin of illness; the way to health and salvation was through the consumption of vegetables and water. The cry of "total abstinence, vegetarianism and women's rights" was

the battle cry of the nineteenth century "food reform" movement (Deutsch 1977). Table I summarizes the illnesses and moral attributes thought to stem from the consumption of meat and meat products. While we may chuckle at the list there is one disease attributed to meat consumption which has a modern ring, namely, "arteriosclerosis". If there is one health problem with which we are concerned and

which has been connected to the consumption of animal products it is diseases of the cardiovascular svstem.

Migraine

Muscular weakness & "Diseases

27

a

Neuralgia Sci atica Constipation Intestinal fermentations Auto

-in

to x ic atio n

s

CARDIOVASCULAR DISORDERS AND THE CONSUMPTION OF MEATS The cardiovascular disorders, which are summarized in Table 2, are degenerative diseases that afflict a significant number of people in North America. It is generally conceded that the suppression of infectious disease and the attendent increase in life span is one of the prime factors in the increase in the incidence of manv desen-

Table 2. Brief descriptions of the major types of coronary diseasest Type

Arteriosclerosis

Degenerative changes in the arterial wall marked by loss of elasticity. The lumen

of the artery may be reduced by a thickening of the wall and/or deposition of Atherosclerosis

Thrombosis

Myocardial infarction

calcium within the wall. A particular type of arteriosclerosis in which fatty, fibrous deposits form on the intimal layer of an artery. These deposits are called atheroma and they rnay deform and constrict the lumen of the artery in advanced stages. The blockage of a blood vessel by a blood clot which prevents the flow of blood to tissues beyond the point of blockade. This may result in the death of those tissues. Localized death of the heart muscle because of obstruction in the coronarv arteries.

Angina pectoris

Severe pains produced the heart muscle.

tAfter Brown and Omura (1975). iosclerosis and atherosclerosis.

by either relative or absolute decrease oxygen supply

In the nineteenth century there was no distinction

to

made between arter-

28

CANADIAN JOURNAL

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It is estimated

that 29 30 million North Americans have some form of heart or blood vessel disease. Of that number 23 - 24 million have hypertension and 4 - 5 million have coronary heart disease. Nearly one-half of all deaths are due to cardiovascular disease: atherosclerosis accounted for some 900 000 deaths in 1974 (Krehl 1977). The American Heart Association estimates the cost of erative diseases.

cardiovascular disease to be

of $27 ease

x

in the order

10e. Clearly, cardiovascular dis-

is of major

concern. Interestingly

enough it was also of considerable interest in the nineteenth century and many of our thoughts on the aetioiogy of cardiovascular disease have not changed very much from

the basic idea put forth then to the effect that arteriosclerosis was the result of injury done to the arterial system (Tibbles 1914). The involvement of meats in cardiovas-

cular disorders centers on atherosclerosis. The generally accepted connection between diet and atherosclerosis has its origins with the work of Page (1945), Page et al. (1957) and Keys (Keys 1950; Keys and Anderson 1954) in this century and Virchow in the nineteenth century. Keys (1950) and Keys and Anderson (1954) re-

ported an association between the incidence of atherosclerosis and the level of circulating cholesterol such that persons with higher serum cholesterol levels had

a higher incidence of atherosclerosis. Not long afterward

it

rvas found that the level

of saturated fat in the diet was also related to the level of cholesterolaemia (Kritchevsky et al. 1954; Arhens 1957; Arhens

et al. 1915). Substitution of polyunsaturated fats for saturated fats produced a decrease in the level of circulating cholesterol (Arhens 1957). The depression in circulating cholesterol was of clinical sig-

nificance in some cases while in others the levels of cholesterol were above the 225 mg/dl considered normal. The literature surrounding the connection between cholesterolaemia, circulating lipids and atherosclerosis is voluminous and the reader

is referred to a number of excellent reviews for detailed information (Gotto et al. 1976: Ross and Harker 1976; Kritchevsky 1976, 1979; Krehl 1977). The lipid theory for atherosclerosis can be summarized as follows: 1. Feeding experimental animals such as rabbits, rats and dogs diets which conLained 27a-57o cholesterol (as pure cholesterol) produced a lesion which was similar to human atherosclerosis. 2. The experimental lesions mentioned above are laden with lipids. 3. There is a strong statistical association between the incidence of atherosclerosis and circulating cholesterol, that is, a larger number of persons who die of cardiovascular disease have higher circulating levels of cholesterol. Since eggs, meat and milk contain appreciable amounts of cholesterol (Table 3) the medical profession recommended that the intake of these be decreased in the average person's diet. This position has been a matter of faith ever since the 1960s and woe betide those who disagree as the Food and Nutrition Board of the National Research Council (NAS) found rvhen they questioned the idea in a recent publication (

1

980).

There are a number of criticisms of the lipid theory: 1. The animal models selected such as rats and rabbits may be inappropriate' Rabbits, for instance, do not ordinarily have large amounts of cholesterol in their diets and may not be able to metabolize exogenous cholesterol. Animals such as mink that normally consume a diet rich

in

cholesterol have hypercholesterolaemia

but do not develop atherosclerosis (Zilversmit et al. 1971). In contrast, elephants have lower circulating cholesterol levels and develop atherosclerosis (N{cCullagh 1912).

2. The "logical" premise that both milk and eggs will increase circulating cholesterol levels and therefore should be limited or removed from the diet apparently has

BROWN

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MEAT CONSUMPTION AND HUMAN HEALTH

29

Table 3. Lipid composition of selected meatst

Saturated Nlonene fatty

fatty

fatty

lipid

ac ids

acids (e/dg1

acids

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Meat

Chicken; broiler, roasted Chicken, mature, roasted Turkey, roasted Pork, ham (cooked) Beef, loin, broiled Veal, broiled Eggs, chicken, hard-cooked

Milk, whole Milk, low fat

13.60 r 4.0 9.13 35.00 50.40 13.0 11.15 3.66

r?2

Butter

Polyene

Total

81.11

5.34 .32 3.19 14.70 22.1 5.'72 4.46 1.06 0.56 23.4

3.'79

4.48

5

2.84 1.2.60

24.18

6.24 J. JJ

2.28 1.20 )u. )

Cholesterol

(8/dg; 2.97

88

2. 80

r36

2.48

82

3. 15 1.01

oz 15

0.26

71

1.45

548

0.14

14

0.07 3.0

219

8

+U.S.Dep. Agric., Handbook #8-5. United States Department of Agriculture, Washington, D.C.

not held up to direct investigation. Milk has been demonstrated (Table 4) to be hypocholesterolaemic, if anything. Research with humans fed a reasonable number of cooked eggs indicated that ingestion of eggs had no effect on the level of serum

a demonstration is available under controlled clinical conditions (Arhens et al. 1957; Miettinen 1975), but none of the population studies done to date have shown any connection between hypercholestero-

cholesterol (Slater et al. 1916) (Table 5). Almost all studies done to demonstrate that

gan et al. 1962;' Krehl 1977). More recently there has been a convincing

dietary cholesterol was hypercholesterolaemic used reagent cholesterol and not cholesterol as it occurs in most foods. In natural products such as meat, cholesterol exists as a component of the cell membranes and as such may not be as available to the person or animal as the free cholesterol used in most experiments. 3. The equally logical premise that one should be able to show that dietary cholesterol intake and circulating cholesterol

level are connected in a free-living human population has not been demonstrated. Such

laemia and dietary cholesterol intake (Ka-

demonstration that the simple measurement

of circulating

cholesterol levels in not meaningful. The consenus is that choles-

terol attached to high-density lipoproteins is not available for incorporation into atheroma while cholesterol attached to lowdensity lipoproteins is really available to the atheroma (Kritchevsky 1979; Miller et al. 19'77; Miller and Miller 1975). 4. The atherosclerosis producted in experimental animals by diet may be different from that noted in humans. The most significant difference is that atheroma in

Table 4. Effect of milk on circulating cholesterol and lioid levels in ratst Group*

Whole milk Number

a SEM) Triglyceride (mg/dl- ,t SEM) Phospholipid (mg/dl + SEM) Cholesterol (mC/dL

fAfter Kritchevsky

Skim milk

Control

6

o OJ :l: J

6