The Contribution of Meat to the Diet of Man

THE CONTRlBUTlON

by Albert M. Pearson“

OF MEAT

In t rotltr ct io n

E a rl y re search VI II cida t in g the contribution of meat to thc, diet of inan emphasizcd the positive aspects by focusing upon the essential nutrients contributed through eating Ineat.l.2 In recent years, howevcr, the mccit and livestock industry has followed a defensive, rather t h m offen5ive approach to promoting meat and has largc,ly concentrated upon defending meat from attack. The end result has been an almost constant battlc to combat every nep t ive statement about meat consumption. In essence, the industry has been con- stantly eitgagcd in putti!ig out a series of brush fires, when more effcctive iesults might have been ob- taiiiul had thev concentratcJ upon the positive 1111-

tritivc values of meat consumption. Obviously, thew may well he reasons for combating policy oriented attacks, such a s the report of the Senate Select Coin- mittce on Dietary Goals,3 hut it is questionable if stateinmts by less prestigious groups are worthy of a resprnse. In fact, an argumentative “pseudo-scien- tist” may be more disappointed by the lack of a reply than if debated throu& the media, because he revels in acknowledgeinent that his viewpoint evokes a reaction.

A far morc’ uscbful approach to promoting meat consumption can be foiind b y expanding the support of rescwch on the bcnefits cl f meat in the diet. Such rcwarch should concentrate upon the role of meat in mecting dictary requirements and its positive effects upon health. It is our cc~ntention that funds spcwt in supporting rcsearch will pay far greater clivi- deild5 than those expended in promotion.

The material to bz presentcd herein will, therefore, concentrate upon the basic contributions of meat to the diet. We will in scime instances refer to some dis- crcpancies in thc literature c r attacks by the media, which arc contrary to the preponderance of evidence. Iievcr-the-lcss, i f avail,~blc data suggest that meat consumption does, in fact, contribute to h d t h problems, this too will he poiittcd ut. Certainly, the meat indiistiy must face established facts and try to recon-

“A. AI. PEARSON a i d R. I . BROOKS Deportment of Food Science cintl Human Nutri- tion, Michigan State Unicersity, East Lan.;in,n, Michigun 4iyhi.24

TO THE DlET OF MAN

cile its policies. In view of the similarity in composi- tic n and the difficiilties involved in separating the contributions of meat, poultry and fish, we have broadly lumped them together for thc sake of this discussion and will simply refer to all three as flesh foods or more simply meat.

Classification of Nutrients

The similarity in the composition of m w t and that of the hnmari bodv is striking, in fact if one compare's the cntirc bodv of ineat animals and that of man, one finds them to be very similar.4 This suggests that meat would provide a nearly pcrfect balancc of nutrients. However, lest we become obsessed with the idea that animals should provide all human dietary needs and that we should exist upon meat alonc~, let CIS remember that tlie meat producing species are capable of transforming plant materials to meat. Fur- thermore, animal tissues alone will not provide all of the essential nutrients-at least in the kinds and amounts needed by man.

The major classes of nutrients consumed by man in- cludc proteins, fat ( lipids), carbohydratcBs, vitarnirri and minerals, which along with water provide our dietary needs. If all of these nutrients are provided in the pioper proportions, they will not only supply the energy needed but also all of the nutrients required to carry on thc body’s vital processcts. Our discussion herein will not only focus upon the classes of nutrients, hut also upon some of the advantages antl dis- advantages of rncat in thc diet.

Carbohydrates

The carbohydrates include the sugars, starch, cellu- lose, g~uins and a nuniher of rcblatetl substances. Only 0.4 g of carbohydrate per capita per (lay comes from meat, poiiltry antl fish (Table 1). This supplies only 0.1% of our dailv intake (Table 2 ) , yet carhohytlratc-s pr(Jvidc a major source of energy for both man and animals. Evidence suggests that carbohydrates not only provide energy, but play key role in providing dietary hulk, and thereby. contribiite to bowel move- ment and elimination of toxic ccmponents from the systc.m.?o

\!eat i \ not ‘in important mircc‘ c.f carhohydrate, in fact, the amount contributed is nc>gligible. Thuc,

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AMERICAN MEAT SCIENCE ASSOCIATION

TABLE 1

CONTRIBUTIONS OF

Uni ted S t a t e s

MEAT, POULTRY AND FISH TO THE RECOMMENDED DIETARY ALLOWANCE IN THE UNITED STATES

Red Mea t P o u l t r v Meat F i s h F l e s h Contr ibut ion f r o m mea t , Recommended _____

Daily Amoun t 55 of Amoun t 7p of Amoun t 76 of pou l t ry Allowance Suppl ied Total Suppl ied To ta l Suppl ied Total a n d fish

N u t r i e n t (RDA) (:I per day'h RDA(L per day( '> RDA'C p e r d a y ( " RDA(< A m o u n t (4

Energy

P r o t e i n

Fa t

Carbohydrate

Cal c i urn

PhosphorJs

I r o n

Ilagnes i ui:i

V i tamin A Vi ta i i i i n C

T h i a m i n

x i b o f l a v i n

N i a c i n

V i tai i i i n Bf3 Vi tamin E 1 2 Fol a c i n(

Z i n c ( e

Copper(

2700 Kca l 56 g r a m n o t e s t a b l i s h e d *Ot e s t a b l i s h e d 300 mg 803 I?q

10 Imgk

350 iiiq

5000 I . U . 45 mg

1 . 4 m(l

1 c mg

2 .0 lily

3 . 0 3

400 y 15 mg

1 .6 IJig

- - -_ - -

~ " R e f c r e n c e KO. ti ' ~ IRefe rence No. 1

1 )Ca lcu la t ed ab fol lows: ',; KUA

"Refe rence KO. 25 ClReference No. 26 ' )Re fe rence No. 27

575 Kcal

31.4 5 48.3 g

0 .4 g 22.2 ni9

31 0 . 9 i'ig

4 .7 mg 31.8 m3

1492 I.U. 1.18 n'g 0.43 mg 0.43 mq 7.26 "3

0.58 1'19

5.22

17.5 .Ag 7.1 mg 0.21 no

21.3

56.1 - - - - - - - -

2.9

38.9

47.1

9.1

29.8

2.6

34.3

26.9

43.7

29.2

174

4.4

47.3 ----

67.6 Kcal

9.5 q

3.5 q

5.7 mg 39.5 m7

0

0.82 mg

11 .5 ng 312 I . U . 0

0.03 rng 0. 15 mg 2.55 mg

0.44 mg 0 . 3 0 ', g

5 99 LIg 2.8 rng 0.29 rnq

2.5

15.3 _- - - _- - -

0.7

11.2

8 .2

3.3

6.2

0.9

2.1

9.4

14.2

21.9

26.5

1 . 5

18.7 - _ - -

EIBased on a d u l t man. Va lues f o r t h e a d u l t p remenopausa l women a r e 18.7 mg/day

30.0 Kcal

3.9 4

1.4 g 0.0

8.6 niq

0 .22 iqg

4 E r!q

5.6 ng 25 I . U . 0.12 rng 0.01 rnq

0.02 ng 1.05 ng

0.06 mg 0.82 llg

2.10 ;,g 0 . 2 niq

3.07 mq

1.1

7.0 _- - --- 1.1

5.7

2.2

1.6

0.5

0.3

0.7

1 .2

5.8

3 . 0

27.2

0.5

1 .3 ---

672 Kcal

43 .8 9 53.2 9

0.4 g

37.1 rnq

446.4 my 5.74 rng 48.9 mg 1529 I . U .

1 . 3 mg

0.52 mg

0.6 nig 11.4 mq

1 .08 mg

6.84 119

25.59 uq 10.1 rng

0.48 mg

24.9

72.4 ---- ----

4.7

55.8

57.4

1.4.0

36.5

2.9

31.1

37.5

63.7

54.1

228

6 .4

67.3 ----

nian should consume ccwal grains. vegc>tables and h i i t , ncit only to provide fcod encrgy and vitamins. but more importaiitly for bulk.

Fat ( Lipids)

Fat, like carhohytlrate, is an important dietary sotircc' of encrgy. In addition, dietary fat must pro- vitlc certain eswitial fatty acids, because of man's indiility to synthesize them. Generally, linoleic, lino- lciiie and arachadonic acid arc considered to be essential, although strictly speaking only linoleic and y-linolenic acid are essential since arachadonic acid can be synthesized if adequate quantities cf dietary linoleic acid are supplied.5 One kmwn function of the esscntial fatty acids is to serve as preciirscrs for ~~rostaglandin biosynthesis.

quate aincunts of fats and oils, fatty acid deficiencies are seldom encountered. Only i n cases of impaired absorption are fatty acid deficiencies likely to occur.6

Although meat fat provides the essential fatty acids in adequate amounts for inan, many of the vegetable oiIs provide richer sources. .4 far more important characteristic of animal fats may be the fact that they are more satiirated, and are, thus, Iws SIIS-

ceptible to autoxidation.7

Amount of Animal Fats. Animal fat in the dict of man has come under ccnsiderable attack for two reasons: (1) because of the amount of fat in the diet;3 and ( 2 ) because animal fats contain a relatively large amount of saturated fatty acids, which have h e n claimed to be atheriogeikS,g Although the validity of these two pnints has bccn cltiestic:necl, the story is

Siiice the norn1.11 dict of 111an usually includcs ad-- not entirely clear at this time.

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TABLE 2

CONTR.IBUTIONS OF MEAT, POULTRY AND FISH TO THE TOTAL DIETARY INTAKE IN THE UNITED STATES(.

o f t o t d l consumption

Avcra;e pc- o f t o t a l o f t o t a l o f t o t a l c o n t r i b u t f d by meat, c a p i t a consumption consumption consumption

consump 1on c o n t r i b t e d c o n t r i b u t e c o n t r i b u t e d qoul t r v and f i s h -_ p e r . __ daytb _____ by pou l t r y t b by f i s h ( b ___._ ~-

'4u t r i e!t by nieatyb -

Energy

P r o t e i n

Fa t

3380 Kcal 17.0 103 gra18ij 30.5 159 grams 30.4

Carbohydrate 390 grams 0.1

P tios p horus 1 5 7 0 riig 19.8

I r o n 13.7 nig 2 5 . 2 Flagnesi um 349 mg 9 . 1 V i ta i i l in A 3200 I . U. 18.2

Vi ta i i i in C 113 mg 1 . o

Ca 1 c i urn 950 irig 2.4

Thiamin 2.08 rng

R i b o f 1 a v i ri 2.52 mg

N i a c i n 25.2 nig

V i t a m i n 136 2.23 lllg

Vi tamin B12 9 . 7 &,Cj

23.2

17.2

31.2

25.6

53.8

2 .0 9 . 3 2 . 2 0 .0 0 . b 5 . 7 4.4

3.3 3.8 0 . 0 1 . 6

6 . 0

10.0 19.2 8.2

0.9 3.3 0 .7 0 . 0 0.11 2 . 9 l . i 1.6

0 . 3 0.1 0 .5 0 . 7

4 . 1 2 . 6 8 .4

19.9

42.6

33.5 0.1 3 . 9

l ' ; . 1

30. \ l 14.0

22.3

1 .1

1 5 . 3 1 4 . 1 4 5 . 3 4 7 . 4

70.4 F o l a c i n * - - - - - - - - - - - - - - - - _ _ _ i i nc* - - -_ Copper* ----

- - - - - - - - - - - - - - - - - -_ ---- - - - - _ _ _

a)The average y e a r l y per c a p i t a consulliption (carcass b a s i s ) amounted t o 194.7 I b s o f r e d inieat, 5 2 . 9 11)s o f

b)Reference No. 4

* Values n o t a v a i l a b l e

p o u l t r y and 12.9 lbs o f f i s h in 1977. A l l da ta a r e p resented on carcass bas is . 9eference '10. 4

Figure 1 clearly shows that total fat consumption has increased by some 25%,10 since the 1910-13 base period, which is given an arbitrary value of 100%. It has also been suggested that there has been an increased incidence of coronary disease during this same time period,2 although no one would deny that part of the increase is the result of better statistical

of death. The question as to not animal fats are responsible for the increased death rate mav be best answered b\, exam-

for all of the increased fat consumption, hiit also im- plicates polyunsaturated fatty acids (PUFAS) as being a more likely contributor to the increascd ratc of coronary heart disease in the past 60 years.

There are two main reasons that high levels of fat in the diet are objectionable: (1) the Iiigh caloric intake due to increased fat levels in the diet; and ( 2 ) evidcnce that high dietary fat consumption may be responsibk for an increased incit~ence of CRIIcCr. Ill

of

, ining Figure 2, which shows the sources of nutiient fat at different intervals of time from 1909-13 through 1973.10 This graph clearly shows that per capita fat consumption increased from 1%5g per day for the base period to 156g in 1973, an increase in total fat consumpticn of 31g per day. Consumption of animal fats declined by 9% in this period, whereas consumption of vegetahlc fat increased some 3-fold. This not only would suggest that vegetable fats are responsible

regard to the former, it is well known that fat prc- vides 2.25 times as much energy '1s an eclual cluantity of carbohydrate or protein. Thus, unless energy intake is carefully controlled a5 levels of fat in the diet arc raised, there is a marked increase in the incidence of obesity. Unquestionably, thi5 was one of the major factors influencing the Scnate Select Ck~rnmittcc~ to rcuimmcncl decreasing the nutn1)rr of ca1orit.s from fat from 40 to 3Vi. In all fairness. howcver, the rec-

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YO O f 1909-13

I

~ 100 I

I L - I I

I ' I I r l ' l I I 1 ' 1 1 1 1 ' 1 1 I I ' I ~ I J - l l I I l ' l 1 1 I I I 1 I 1 111 1 , l d d 50 - 1 1 I r I r

1910 1920 1930 1940 1950 1960 1970 1980 5-YEAR MOVING AVERAGE

PRELIMINARY ESTIMATE

UU)A Nf C A R S -7 -76 *I

__ ~~~~~ ~

FIGURE 1

Changes in per capita consumption o f nutrient fat using the 1910-13 base period as 100% and expressing changes relative to that base. USDA data.4

o~nmcndatioii could have been achieved far more easily by merely reducing total caloric intake, since ;I reduction in fat content could be easily counter- b a l a ~ ~ c e d by increasing carbohydrate consumption. Fi- nally, as already pointed out, the increase in fat consumption has come about by increasing vegetable fat, whcreas, animal fats have actually declined.

Evidence that high fat levels in the diet may increase the incidence of cancer come from several soiirces.20~21 First, there is some evidence that obese women have a greater incidence of endometrial cancer of the uterus than women of normal body weight. This has been explained by the fact that conversion of steroid hormone precursors to estrone occurs in the fatty t is~iics.~~*41 Furthermore, there is similar evidence for a higher incidence of kidney cancer in obese women.

Furthermore, there are frequent references in the literature indicating that high fat levels in the diet

may contribute to a greater incidence of cancer of the lower bowe1.20-24 Although these studies have shown that the incidence of tumors increases on high fat rations, there is no clear-cut information showing dif- ferences between various types of fat. Thus, there does not appear to be any reason for an increase in the frequency of cancer due to consumption of animal fats as compared to vegetable fats or vice versa.

The final piece of evidence indicating that high fat diets may contribute to more cancer comes from two recent reports by Shamberger et ul.,14J5 in which malonaldehyde is implicated as a carcinogen. How- ever, the data are not convincing and the values reported for malonaldehyde do not agree with values found in our laboratory.16 Finally, if malonaldehyde is indeed a carcinogenic substance, the unsaturated fats are more likely to be involved than the saturated fats. Vitamin E and selenium could serve as protec- tive agents by blocking free radical formation as shown in Figures 3 and 4. Since unsaturated fats

-47-


SOURCES OF NUTRIENT FAT (Grams)

1909-13 .....

125 . . . . . . . . . . . . . 2 1 ::;.;:; . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . ..

1935-39

133 1947-49 . . . .

141 1965 . --

145 1972 . . -

156

b e g e t a ble 'Ani rn al PERCAPITA P E R DAY. & P R E L I M I N A R Y

FIGURE 2

Changes in the sources of nutrient fat in the diet in U.S. for 1909-13 base period through 1973. USDA dota.4

oxidi7e morc readily that saturatecl fats, it is cloubt- ful if meat lipids w o d d be involved to the same ex- tent as vegetable oils iinlcss the lattcr arc protectcd by antioxidants.

In summarizing the data on fat consumption let us refer back to Tables 1 and 2. which show that cut of a total per capita daily intake of 159g of fat, only 53.2g cr one-third comes from consumption of meat. poultry and fish. Most of the rc~maincler is derivcd from vegetable oils, as shown in Figure 1. It is re- emphasized that total animal fat intake has declined by 9!% since the 1909-13 base period, whereas vcge- t'iblc fat consumption has incrc,aseci by 3-fold.

Saturated cs Unsutiirated F a t t y Acids. The controversy concerning saturated versus PUFAS relati1.e to their role in coronary heart disease has already been referred to herein. A series of three contrasting papers have been published on the subject,11J2J3 whicbh make extremely interesting r cd ing , and are

callecl to thr attmtion of readers, not only because of thc controversy on the topic, h i t also beeaim. ot the amount of heat g tmmted . A morc cool hc~adtd approach to the discussion cvoiiltl suggest t l u t even though PUFAS will l o u w serum cholc~stcrol, this approach should only be nsrd i n cases of high risk p.1- tients and not for the g c w d public.

411 of the evidence prc.sented wonlcl cast rlon1)t on the validity of criticizing meat becausc of its high saturated fat content. First, the cpidcmiological data shown in Table 3 would indicate there is no clear- cut relationship between incat consumption and the incidence of cardiovascular cliseasc.l7 In fact, Finlantl, in which iiwat eoiisiimptic;~~ is thc. lowest. s l~o~vcd thc highest incitlencc~ of coronary hcart cliseasc.

The sc~on t l piece of evidcncc,, which casts doulit OII the validity cf changing from a saturated to an unwtiirated fatty acid containing diet. also i y taken from the siiminary by Shorland'7 and is srimn1ari;lcd

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H20 + ' / 2 0 2

Chemical damage to // critical SH - proteins cotolase

ENZYME SYSTEMS AS XANTHINE OXIDASE, AMINO ACID OXIOASES,etc.

OXIDANT STRESSORS

ROH + H,O U N SAT URATE 0

LI PlOS

Lipid peroxidation Malonic dialdehyde, etc. Cell damage

Vi tamin E "block<' reaction 0. Se, os a component of GSH-Peroxidase, catalyzes reaction 0.

FIGURE 3

Scheme showing the postulated mechanisms of interaction between selenium (Se) and vitamin E in preventing oxidant damage. Taken from Hoekstra.53

in Tablcxs 4 and S . The data show that only in the Protein experiment by Morrison18 was the incidence of deaths from coronary heart &Tease significantly decreased ( Table 3 ) . In this case, the only difference between the treated and control groups was the fact that the control group were not on a diet, whereas the treated group were limited to 1500 calories per day without restrictions on the kind of fat. On the other hand, the study by Dayton et a!.'g showed that changing from a saturated to an unsaturated diet decreased the number of atherosclerotic deaths, but yet overall dcaths were essentially the same. In fact the authors concluded, "Total longevity was not favorably affected to any measarable degree, deaths due to non-athcr- osclerotic causes numbered 71 in the control and 85 in the experimental group." The authors noted that

The high quality of meat protein? is well cstab- lished and is unquestionably one of the major reason? for eating meat. Although protein quality appears to be less critical with man than with a number of species of farm animals, growing children show reduccd growth and other protein deficiency symptoms unless provided with animal p r o t c ~ i n s . 3 ~ ~ ~ ~ Some of the deficiency symptoms noted on Zen macrobiotic diets can also be traced to protcin deficiency.*& This does not mean that people must eat meat to maintain good health, as it ir well known that Seventh Day Adven- tists are a healthy group, but merely that it is diffi- cult to rcinain in good phy\ical condition and exclude all animal proteins, i.e., meat, eggs and milk.zg,31

v -

the lower dcxath incidence from atherosclerosis was accompanied by a higher incidence of cancer. Thus, the only effective means of redncing tlraths was by controlling caloric intake.

Tables 1 and 2 show that meat, poultry and fish arc supplying 4.8g protein per capita per day, which makes up 78% of RD,4 for an adult man. Generally, the population in the IJnited States consumes n great

-69-


I ti ~ ~ 4 ~ c h e m e illustrating propagation of free radical damage I I

I Hydrogen abstraction - causes a free radical of unw! i ra t rd lany J( 111 II Peroxy free radlcal lorms lrom reacllon wlth 0,

to membrane phospholipids, laterally whin the hydrophobic plane

peroxidase. Free radicals may arise from endogenous SOuIces, as from hydrogen abstraction by electron transport, or exogen- ously from substances in the environment or photochemical

Of a and the actions Of E and glutathione III Hydroperoxlde forms by reduction o~ peroxy radical Iv Oxyradtca1 arlslng by homolytlC scission V Hydroxy compound arrsmg from action 01 glutalhlone peroxidase

Qwnchong pe~oxv rad,cal by dl ,,.tocopherol rnechanlsms VI1 dl-,t-locopherol will decompose possible reduction 01 radical by electron trdnsporl

FIGURE 4

Scheme showing propagation of free radical damage to membra ne phospholipids indicating the probable role of glutathione peroxidase (GSSG) and vitamin E in blocking the reaction. Token from Packer and Walton.54

excess of protein with daily per capita protein consumption amounting to 103g, which is nearly twice the RDA of 56g per day. Of the total protein consumed 42.6% is derived from meat, poultry and fish.

In spite of the high level of high quality protein in thc average human diet, some evidence for deficica- cies have been reported to occur in young children shortly after weaning." In such cases, it seems likely that the total protcin intake is far below average due to cither their economic status or their consumption of strict vegetarian diets. Regardlcv,s of the reason, inclusion (if small amounts of meat, poultry and fish in the diet ~hou ld almoit m i \ ersally eliminate the deficiency probleins.

Vitam ins

this grcup to he considcrcil further mill 1x1 vitamin A. Vitamin A is localized in the liver or in th(, f'ltty tissues, largely as its precimor p-carotene.

Tables 1 and 2 show7 that meat, poiiltry and fish contribute about 22% of the total vitamin A int'lk(\, but this would meet some 364 of the total rcyiiirc- ment. Thus, the flesh foods make a significmt tori-

tribution towards the total dietary intnkc and to the RD-4 for vitamin A. Thc iniportancc of fled1 foods ac a dietary sourccx of vitamin A should also IX notcd sincr the 10-state iiutrition~l stiidy intlicLitcd f r c b -

queiitly low serum vitamin A Ic.vc~ls iii the popu1,i- tion.31p32

Vitamin C. Ascorbic acid oi vitamin C is the first of the water solublc group of vitamins to lie (lis- cussed. SIeat. poultry a i d fish contribiitc onlv alioiit

A

1% of the total intake. (Table 2 ) a n J supply ~lightl? less than 3% of the 11D.4 (Tahle 1). Thus, incat inakc>s little contiihiiticxi to thc vitamin C n c d s ( i f

m m .

The vitamins, although reciiiirecl i n extremely small qiimtiticls, play vital roles i n the health and rvcll being of man. They are generally divided into two groups: the fat soluble and water soluble vitaminq. Generally speaking, meat is not an irnportant sourcc of the fat soluble vitamins, so thc only member of

Tkiamin. 1Ieat contrihiite~ abciut 0.52 mg of tliin- min or vitnmin 13, townrtl the 11114 of 1.4 rng, or it

- 70 -


TABLE 3 Ribofluuin. Another of the water soluble vitamins

contributes about 37% of the recommended daily allowance (Table l ) . When calculated as to the percentage of total intake, meat, poultry and fish contribute about 25% of the thiamin. Although this makes a substantial contribution to total intake, it still com- prises essentially the same proportion of the total as was reported for 1944-45.' Even though total meat consumption has gone up some 50 lbs. in this period, pork consumption has declined by some 15 lbs., and being much higher in thiamin, may be responsible for the fact that there is little change in the total intake of thiamin.34

is riboflavin or vitamin Bz. I t plays an important role in the oxidation-reduction reaction in muscle by serv- ing as a coenzyme in the transfer of electrons or hydrogen to the cytochromes, which ultimately are re- moved from the system by formation of water.

Meat, poultry and fish supply 0.6 mg of riboflavin per capita per day, which makes LIP 37.5% of the RDA (Table 1 ) . When calculated on the basis of proportion of total intake, meat, poultry and fish contribute about 24% (Table 2). This value is up from 16% in 1944-45.1 Thus, meat, poultry and fish are con- tributing more riboflavin to the diet as a consequence of the increased consumption of flesh foods. Still flesh foods are generally considered to be important dietary sources of riboflavin.

Niacin. The beneficial effects of eating meat have never been more clearly shown than in reducing pellagra from a serious dietary disease to one that is now practically ~inknown.35,~6 Meat, poultry and fish contribute about 64% of RDA for niacin (Table 1). Similarly, the flesh foods provide 45% of the total niacin intake (Table 2 ) , which can be compared to some 401% during 1944-45.' Although other sources of niacin arc readily available, the flesh foods are the most important single source and make an important contribution to total niacin intake.

Vitamin B,;. Pyridoxine, pyridoxal and pyridoxamine comprise the Bo vitamin complex. Meat, poultry and fish provide some 54% of the RDA and contribute

TABLE 4

EXPERIMENTAL CONDITIONS OF DIETARY TRIALS DESIGNED TO PREVENT CORONARY HEART DISEASE('

No. i n Ourat ior i C a l o r i e s F a t L i n o l e i c Cho les tero l I n v e s t i g a t o r s groups ( y r s ) Kca l lday C a l o r i e s ( " ) ( T o t a l FA) p/s(2 (mglday)

Dayton e t a ] . C 422 5- 8 2496 ( 1 9 6 q - T 424 2496

ie re r i C 206 5 ----a ( 1 966) T 206 2387

f l . R . C . C 194 4 2287 ( 1968) T 199 2380

40.1 10 0.2 653 33.9 35 1.5 356

- - - - a Low Low Higher 39.7 39.7 2.4 284

40 40

Mor r ison C 50 12 no t r e s t r i c t e d 40 ( 1 960) T 50 1500 1 5

Research C 129 3 2300-2600 44 Committee (1965) T 123 1900-2000 20

'Taken f r o m Shorland (1973)17

2P/S = Polyunsaturated/saturated r a t i o

%o values g i v e n

Low Low H i qher H i g h 2.0 Lower

Low Low 200-1 800 Low Low 50-70

Low Low Hiqher Low Lnw L.ower

-71 -


TABLE 5

RESULTS OF DIETARY TRIALS DESIGNED TO PREVENT CORONARY HEART DISEASE(' ', Decrease

Serum Myocard. Sudden Atheroschlerot ic Yon-Cardiac Total Inves t iga tors W L Cholesterol I n f a r c t . Death Deaths Deaths Deaths - Dayton e t a l .

( 1 9 6 g --

Leren ( 1 966)

M . R . C . ( 1 963)

c 2 T 6

7 19

44 36

27 12

c 0 4 54 2 7 T 3 1 I? 34* 2 7

70 43*

52 39

c 3 6 38 9 25 T ! l 2 2 30 R 27

_ - _ _ Mor r i son C - 2 2 - - - - _ _ (1 960) T 13

Research c 5 9 2 7 12 20 Cnniniittee (1965) T 6 1 7 2 7 10 1 7

lTakcn f r o n i Shorland (1973)17

*Signi f icant d i f fe rence ( P c . 0 5 ) between control ( C ) and t r e a t e d ( T ) groups

**Highly s i g n i f i c a n t d i f fe rence ( P .: .05) between control ( C ) and t r e a t e d ( T ) groups

71 177 85 1 7 4

4 56 7 46

6 31 1 23

-- 50 - - 31 **

4 24 3 20

47% of the total intake of v i tm~in R,, (Tables 1 and 2) Thiis, the flesh foods aic 'in extremely important dietary soiirce of vitamin B,,. Although other soiirces are avai1,it)lc. if the diet is carefully sc,lectcd, the flesh foods providr a m'irgin of safety that is wilideIy relied upon by coiisiiiiitw i n thi5 countn a i d 11 oulc l he dif- ficult to repl'icc.

Vituriiin R I 2 .A nimd proteins, I\ hich include flcsh foods, milk and eggs, 'irv the major clic.tary sources of vitamin B I J .4 nuinher of s t i ~ d i e ~ ~ T * ~ * have shown that vegetarians havv gieatly rcdiiced levels of vit'i- min H I a \ compcircd to nc:nvegetaridns, )et there i \ little or 1 1 0 evidence of nutritional problems. Never- the-less, '1 nrimber of ccisc histories have shown that person\ sufft.ring from x u t e vitamin R I J deficiency were vcgetai i a n 5 and inclusion of animal proteins in thr diet oi vitamin B I J siipplcmentation allc.viatcd the symptoms. ,4lthough these studies suggest that vegcx- t,irians c m go for long period\ of time (I4 - 15 years i n some instances) withoiit showing any obvioiis vitamin R , ? dclficiency symptoms, thcrc are certain risks o f suffering vitamin 131 : tlckficienc) on vc)getarim diet5.

Meat. poultry and fi\h sripplie5 70.4% of the dverage per capita intake of vitamin D 1 with the other mimal proteins suppl>iIig mrst of the rcmainder (Table 2 ) The total intahe of vitanin R 1 from thc flesh food\ amomts to 22h% of the RI>A (T'ihle 1). Thus, it i5 obvious that prcsent consumption levels of the flc,\h food5 piovide surplus of vitamin HI,, and that the totdl c( riiiimption of flesh foods could 1 ) ~ reduced b y about half arid still meet the 1l1>,4. If 611e were

to rely on other fcocls, including dairy products arid eggs, to meet the llD,4, only approximately 37% of the recommended level would he supplied. At cur- rent levels of consumption, eggs supply some 8.W of thcx total vitamin B,, intake, whereas all dairy product\ pmvidc 20% and all other foods (excluding the fle5h foods) provide only 1.5% of the total. Thus, meat, poultry and fish are extremely important dietary wiirces of vitamin H I ? , assuming that the H D A provides '1 reasonable estimate of needs.

Folic '2citl. Table 1 reports the avcmge daily per capita int'ike of folacin from flcsh foods. Meat, poultry and fish supply 25.6 pg per capita per day out of 400 pg HDA. Thus, the flesh foods contribute only 6.4% o f the total fol'icin intake, which means they make only n token contril~ution toward the total dietary folxin net& of man.

A f itie IW Is

The iniiierals c m be tlivitled into two classes de- pending upon the amcunt required in the d k t , name- ly, the, minerals reqiiired in relatively large amounts and thosc, rcquired in only trace amounts. Those required in rvlativcly largc mounts include calcium, phosphorus and m'ignesium, whereas much sinaller amounts of iron, copper, zinc and cobalt are required.

Data on the contributions of meat, poultry, and fish to the llDA are presented in TabIc 1, whilc Table 2 shows the percentage of total intake provided b y the flesh foods. Although meat does not make a

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major contri1)iition to the intahe of certain minerals, i t 15 thr m~i jo i dietary soiii cc for others. Thus, sevcrd of the cxswntial miiic>icils 11. ill br discussed sepr'ately

Calcizini. \Ieat 'is commonl> eaten contains only small amounts of calcium and generally is not an important dietary source. Table 1 shows that the flesh foods contribute only 4.77 of the RD.4 for calcium, whereas Table 2 demonstiatc~s that only 3% of the tot'il food calcium intahe is derived from the flesh fO[ l t l \ .

Mechnnicdly dc~honcd or ~nech~inic~illy sep~ratc d meat cont ins milch higher levels of calcium ant1 corild ni,ikr an impc:rtant contril~ntion to calcium intake by ~ n a n . ~ ' ~ The calcium from mechanicall> de- 1:oncd me,it has Ixen sho\vn to l i ~ , r ed i ly nhsor1)ed by r'its, antl their. is no cvidence of an! problems in siipplying the calcium n c ~ d s from this source In fact, thc high calcimn rtintent o f nwchmically de- boned mc.at could provide ;I positive rc '~wn for its i i ' ~

by man.

P h o q d ~ o ~ i r s . \ i ra t , poiiltry and fish arc' e\cc.llcnt s o i i ~ ces ( f phosphoiiis, s i ippl~ ing some 567 of thc. RI I4 (T'iblr 1 ) . Thr flvsh foods a150 frirnish 2'3% of thc, total plio~phorus dietar) intake. Howcver, phos- pl io i115 deficient: is st.ldom encountci c d in man, and other dir.t,irv s( iiiccc c i i ( ' plcwtiful so that the flesh food5, tliougli gcoJ sc iir thc ncYYls of man.

Alagnc.riiim. Thc~ flesh foods arc' not espcviallv good soiirccbs of magncsiuin, siipplying only 14% of thc 1IDA for this mineial (Table 1). The contribution ( f meat, 1x iiltry ,ind f i r h to thc dailj p r capita intake cf magnebiiim J s o comprisc~ only 14% ( Table 2 ) . Evvn tliough the flesh foods 'ire not eyx&illy high i n magnesium, the fact that tot'il intake is the s ~ n e as the USHDA suggests that i t would hr unwise to greatl) reducc or completc~ly replace meat on the diet without carefully subitituting to cbtain at least an cqiial amtinnt of magnesium

Iron \le.it, poultry and fish pro\ide 'in eucellent dietdry source of iron-the first of the trace minerals to be di5cusScd. Table 1 shows that the flesh foods provide 57.4% of the RDA for the adult man, whereas Table 2 reveals that the flesh foods provide alioiit 31% of the total intake. The average per capita intakc of iron - per day amounts to 18.7 mg, which is well in eyce5s of the 10 mg USRDA for the adult man, but provides only the amount needed for pre- menopa~isal woinen.42 Even though these values in- dictate that total iron intake meets the RDA for both men and women (on average), the 10-state nutritional study indicated liorderline iion deficiency is

a common nutritional problem in the U.S., especially in growing childrcw and l~ rc~~cmopausa l omen.^^.^^ Furthermore, recent stiidies42-4: have shown that the form of iron ( heme versus non-heme) and other dietary factors ( Ievc~l of ascorbic acid and "meat factor") can grcx'itly influence, ii cn absorption. Thus, wbclini- cal levels of iron deficiency may be a common problem i n t h r L U.S., in 5i3itc of seemingly adequate levels of intahc.

\Ions( n and 0 t l 1 t ~ s ~ ~ ~ ~ ~ pointed out that the RDA for ir(in intalc, of pr(menopausa1 women was established at 1S.7 mg Fer (lay on the awimption that 10% ahwrptioii of iioii occurs H(,\vevcr, several stud- 1c+4~'j M it11 radioactive labelcd iron h ~ t c shown that abscrption from vegctahlcs m d cereals is usually less than 5% as c o m p a r d to 15-2M for souices such as beef. liver antl fish The tliffcrencc, a t least in part, can ??e cxplC~inecl hy the higher absorption of heme as cornpard to non-h(me iion, hiit the f l e h foods have a lso bwn 5ho1vn to c u h ~ n c e the absorption of n c n-h in(' iron For c~\ample, 1,ayrisw and a s s ~ c i a t c s ~ ~ demonstr,itcd th,:t c ~ l x ) r p t ~ o ~ ~ of a small qumtity of iiiorgmic il oLi 11 a s 10-fold gi rater whc~n taken with vral muscle, than when iiigcstvd with a m e d of maize alone Ccok m d c o - ~ v o ~ hers44 showed that beef, lamb, pork. l n er, 6511 m d rliicheri increased iron absorption 2- to 4-folc1, ~ h ( ~ 1 c n s niilh. ch iwe and cgg did not iiicre,ise 11 0 7 1 absorption. Tliiis, the flcxsh foods were demon s tra tetl to t nhan ce the ahsorption of non-heme i ion In addition to the flcsh foc:tl'5 effects upon iron ab~orptic 11, a\corbic ,>cid 11 i c also bcwi \hewn to increase i r ~ n h o r p t i ( ~ i 1 . 1 ~

C.11culations presented by \Ionson ct ~ 1 . 4 2 infer that for 9% of pr~,~n~,iiop'i"is'il M~OIIICII to attain iron bal- m c e would iequiie mi int,ike of 15 ing of iron in fords h,iring high iioii ,ivailnbility or 18 m g of iron from footls of mcdei a t r iron availabilty . One of the best means r f ass1irmg ircn halmce is to regularly include meat, podt r> o r fish in the daily diet.

Certain other foods such '15 phosphovitin from eggs and phytates frc in \. egetables, are known to decrease iron ~vail ' ildit> in the diet. Thus, the importance of the "meat factor" in iron absorption becomes even more importmt in the diet.

Zinc. The 5eCoIld trace mineral included in this dis- c~ission is zinc, which mas not recogniied as being an cssenti'il element until 1955. At that time, Tucker and Salmon47 reported that porcine parakcratosiy re- sponded to zinc supplementation, while simultaneous- ly \'alIee4' and a ciates repoxted their earliest studies on the rolc of /inc metabolism and its relationship to livcr diwase 111 the hiimm. Saxistend49 has reviewed

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the importance of zinc in the diet of man, and has pointed out that zinc deficiency causes dclaycd gronrth and sexual maturation, results in hypogeusia ( impair- ment of the sense of tastc) and delays or impairs wound healing. The not uncommon ciccurrence of these deficicnry symptoms in the U.S. ~voulrl suggest that '1 considerable segment of tht, popiilation may have A marginal zinc int:ikv.*g

Table 1 demonstrates that mc'it, poultiy ancl fish supply an average daily per capita zinc intake of 10 I mg out of a ltllA\ of 15 mg, or some 67% of the daily rccoinmc.ndec1 allowance. Zinc absorption is rc- ported to fall in the EO-30% range, h i t phytate and perhaps c;ther constitucmts in ce rcds and vegetables complex zinc ancl lo\\er i ts absorption.4q Slrat, poill- try and fish are relativc.1) high in zinc as cm' other animal products a n d providc aiiot1ic.r soiind reason for consuming meat.

Copper. The third tracc mineral tliscussed hrrcin is copper, which plays '111 r.sscritia1 function in ret1 blood crll forination ant1 is ueccssaiy for formation of elastin, an important constititr.nt o f the 'iort't.51

Cartwriglit c i i t d Wintrol)r"z liavcs c~atiniated that thc adult human h d y contains 80 mg o f colqwr, whilc the level in the itewborn is higher pcr unit of liody weight.51 Although copper deficic,ncy has 1,cm 01,- served in man, it is helic.vcd to always be acsoci'ited with other diseases or nutritional deficiencies, arid i t is unlikely that copper dcficicwc\ i t i man is c , iiiscbtl

solely hy '1 lo\v tlictary iiitnke."2

The coppcr rc.ciiiiic.nic,itt for tlic a ln l t h i i n i a i b i s estimated to br rilioiit 2 ing per day . 4 copper intiihv of 3.8 tng'clay w'is found for 16-19 \ ~ a r old Atnc~ricai boys.5' The richrst sources of copp:~ arc the, shell fish and crListaceaiis, the organ mcnti ( 1ibc.r. kiclncy, brains), nuts and dried leginiies, ivliile dairy l i r d iicts and highly refined wheat flour m a low. Table 1 shows that the flesh f w d s contribute appreciable amounts of copper to tlw dirt o f man. Ro\vc.\ CT, tliercs is 1 1 0 evirlencc, that copper intake is inatl(yu~itc*, uii-

less it is confr)iiiided 1)) lo\v proteiii intake> or by ot1ir.r diseases.

CobcJt. Cobalt ill 1~ the last of tracc mincrals discu\sed. Work with ruminnnts h a s clemonstrat('t1 that it is an cwcntial mineral and fmnctions in forin'i- tion of vitamin B,,, which contains about 4% o f cobalt,51 There is no evidence for c o l d t dcficicnc y in man, although vitamin 13] 1! deficiency can occur. IIow- ever, there is no direct evidence for a closc re1 '1 t ' I o n -

ship between cobalt intake and vitamin B I 2 in man,^' assuming that adeqiiate levc.ls of vitamin Hi , arc found in the diet.

1.

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REFERENCES

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34. Heinemann, w. W., M. E. Ensminger, T. J. Cunha 53. Hoekstra, W. G. 1977. Biochemical function of se- and E. G. McCulloch. 1946. The relation of the lenium and its interrelationships with other t race amount of thiamine in the ration of the hog to the elements and vitamin E. Fed. Proc. 34:2083. thiamine and riboflavin content of the tissue. J. Xutr . 54. Packer, L. and Walton, J. 1977. Antioxidants versus 31:107. aging. Chem. Tech. 7:276.

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Documents

The Contribution of Meat to the Diet of Man