Plant Proteins - American Chemical Society

10 Effects of Protein Sources on the Utilization of Trace Minerals in Humans

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 31, 2018 | https://pubs.acs.org Publication Date: June 18, 1986 | doi: 10.1021/bk-1986-0312.ch010

C. E. Bodwell Energy and Protein Nutrition Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, M D 20705 The e f f e c t s of v a r i o u s p o t e n t i a l l y d e l e t e r i o u s components of p l a n t p r o t e i n sources, as i n d i c a t e d by the r e s u l t s of s t u d i e s conducted with humans, are briefly discussed. Examples of c o n t r a d i c t o r y r e s u l t s are g i v e n . I t is concluded t h a t the e f f e c t s of f i b e r , p h y t i c a c i d and p r o t e i n source per se have not been unequivocably established. Reasons f o r the general lack of agreement are d i s c u s s e d . Other components which may a f f e c t mineral utilization are noted. The p r a c t i c a l i m p l i c a t i o n s of consuming s p e c i f i c p r o t e i n sources at customary d i e t a r y i n t a k e l e v e l s are briefly discussed. From a g l o b a l v i e w , p l a n t p r o t e i n s o u r c e s ( c e r e a l s , l e g u m e s , o i l s e e d s , v e g e t a b l e s , f r u i t s ) have a l w a y s been t h e p r i m a r y s o u r c e o f d i e t a r y e n e r g y and p r o t e i n f o r t h e m a j o r i t y of the w o r l d ' s p o p u l a t i o n . In a d d i t i o n , i n r e c e n t y e a r s , t h e use o f v e g e t a b l e p r o t e i n p r o d u c t s as s o u r c e s o f d i e t a r y p r o t e i n , as s u p p l e m e n t s , and as e x t e n d e r s o f more t r a d i t i o n a l a n i m a l p r o t e i n s o u r c e s has been i n c r e a s i n g m a r k e d l y i n t h e d e v e l o p e d c o u n t r i e s . These f a c t o r s a r e r e s p o n s i b l e f o r our i n t e r e s t i n d e t e r m i n i n g t h e e f f e c t s o f p l a n t p r o t e i n s o u r c e s on t h e u t i l i z a t i o n o f m i n e r a l s i n t h e human d i e t . C o n c e r n s have been f o c u s e d on t h e v a r i o u s c o n s t i t u e n t s present i n plant p r o t e i n sources or p r o d u c t s w h i c h may h a v e , f o r t h e most p a r t , deleterious e f f e c t s ; numerous r e c e n t r e v i e w s d e t a i l i n g v a r i o u s a s p e c t s have been p u b l i s h e d ( e . g . , 1 . - 1 8 ) · In the c u r r e n t d i s c u s s i o n , e m p h a s i s is p l a c e d on t h e s t a t u s o f our c u r r e n t knowledge a b o u t t h e e f f e c t s o f f i b e r , p h y t i c a c i d and p r o t e i n s o u r c e p e r s e . This chapter not subject to U.S. copyright. Published 1986, American Chemical Society

Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

10.

BODWELL


Effects

of

Utilization of Trace Minerals in Humans

109

Fiber

R e s u l t s f r o m some r e c e n t s t u d i e s (19-36) on t h e e f f e c t s o f f i b e r a r e summarized i n T a b l e I . F o r t h e most p a r t , t h e r e s u l t s a r e from m u l t i - d a y b a l a n c e s t u d i e s . However, T u r n l a n d e t a l . (3j>) u s e d t h e s t a b l e i s o t o p e f e c a l m o n i t o r i n g method t o a s s e s s z i n c u t i l i z a t i o n and S i m p s o n e t a l . (24) measured i r o n a b s o r p t i o n from a s i n g l e t e s t meal · U t i l i z a t i o n o f i r o n was n o t a f f e c t e d a t l e v e l s o f 9 t o 26g b r a n / d a y from c o r n o r wheat (19, 2 0 , 26.) o r by 16 g of b r a n / d a y (25). N e g a t i v e b a l a n c e s were o b s e r v e d by M o r r i s and E l l i s (21) d u r i n g t h e f i r s t b a l a n c e p e r i o d w i t h d a i l y i n t a k e s o f 36g b r a n b u t n o t d u r i n g t h e s e c o n d 5-day b a l a n c e p e r i o d . H o w e v e r , S i m p s o n e t a l . (24) f o u n d a marked i n h i b i t i o n o f non-heme i r o n a b s o r p t i o n f r o m a s i n g l e t e s t meal w h i c h i n c l u d e d 6 g o f wheat b r a n . With a d i e t w h i c h p r o v i d e d 3 5 g / d a y o f NDF ( n e u t r a l d e t e r g e n t f i b e r from b r a n b r e a d ) , i r o n b a l a n c e s were d e c r e a s e d (26) compared t o t h e 9 o r 2 2 g / d a y i n t a k e l e v e l s . K e l s a y and c o - w o r k e r s (27,28) o b s e r v e d no e f f e c t s on i r o n b a l a n c e o f i n c l u d i n g 2 4 g / d a y o f NDF from f r u i t s and v e g e t a b l e s ; h o w e v e r , n e g a t i v e z i n c and c o p p e r b a l a n c e s were o b s e r v e d . In a second s t u d y (29), lower z i n c , b u t n o t c o p p e r , b a l a n c e s were o b s e r v e d a t i n t a k e s o f 25g N D F / d a y ; l o w e r i n t a k e s (10, 18g NDF) had no e f f e c t . In t h e s e s t u d i e s , t h e e f f e c t s o f o x a l a t e s (from s p i n a c h ) may have a f f e c t e d m i n e r a l b a l a n c e s . In a t h i r d s t u d y , a c o m b i n a t i o n o f c o n s u m i n g s p i n a c h e v e r y o t h e r day p l u s a d a i l y f i b e r i n t a k e o f 26g NDF r e s u l t e d i n i n c r e a s e d f e c a l z i n c e x c r e t i o n and n e g a t i v e b a l a n c e s (37). I n s e v e r a l s t u d i e s ( e . g . , 30~2J>, T a b l e I ) , t h e e f f e c t s of i n c l u d i n g "processed" f i b e r sources (fiber i s o l a t e d f r o m n a t u r a l s o u r c e s ) have been i n v e s t i g a t e d . R e s u l t s have b e e n c o n t r a d i c t o r y ; f o r e x a m p l e , 10gm/day c e l l u l o s e d e c r e a s e d z i n c b a l a n c e s i n one s t u d y (30J b u t 30 t o 4 0 g / d a y d i d n o t a f f e c t z i n c a b s o r p t i o n i n a n o t h e r study (36). P r o c e s s e d f i b e r may have e f f e c t s w h i c h a r e not i n d i c a t i v e of the e f f e c t of a s i m i l a r l e v e l of endogenous f i b e r from f o o d s . I n summary, d a i l y i n t a k e l e v e l s o f f i b e r e q u i v a l e n t t o 20 t o 30g N D F / d a y f r o m f o o d s o u r c e s w o u l d n o t be e x p e c t e d t o have l o n g - t e r m d e l e t e r i o u s e f f e c t s on m i n e r a l u t i l i z a t i o n . Phytic

Acid

P h y t i c a c i d has been i m p l i c a t e d , i n b o t h a n i m a l and human s t u d i e s , as h a v i n g a d e l e t e r i o u s ^ e f f e c t on t h e u t i l i z a t i o n o f v a r i o u s m i n e r a l s and i n p a r t i c u l a r i r o n and z i n c . W i t h r e f e r e n c e t o z i n c , p r i m a r i l y b a s e d on r e s u l t s from animal s t u d i e s , a molar r a t i o o f d i e t a r y p h y t i c a c i d t o z i n c o f 12 t o 15 (or g r e a t e r ) has b e e n s u g g e s t e d as a t h r e s h o l d a t w h i c h d e c r e a s e s i n z i n c u t i l i z a t i o n may o c c u r ( 9 j . R e s u l t s f r o m some r e c e n t s t u d i e s , a r e summarized i n T a b l e I I .


PLANT PROTEINS


Table I .

E f f e c t s of Fiber

Effect

Ref.

None

(19)

26g bran per day

Zn,Fe None Cu

(20)

Wheat bran

36g of bran per day

Zn, Fe

(21-22)

Wheat bran Basal diet

3.3,10.9,or Zn,Fe No change i n 18.7g/day balances with bran added 18.5g/day

(23)

Wheat bran

6g of bran per t e s t meal

Fe

(24)

Wheat bran

16g per day of raw bran

Fe,Mg No e f f e c t or increased absorption Zn Decreased a b s o r p t i o n

(25)

White bread

9g NDF per day

(26)

Coarsebran bread

22g,35g NDF per day

Fine bran bread

22g NDF per day

Zn,Fe Retentions s i m i l a r Cu,Mg f o r 9 and 22g NDF d i e t s ; only deleterious effect observed was t h a t i r o n balances decreased on 35g NDF d i e t

Whole meal bread

22g NDF per day

Source

Fiber Intake

Mineral

Wheat bran

14g per day

Zn

Wheat or corn

a)NDF=neutral detergent

Negative balances, 1 s t 5-day p e r i o d ; p o s i t i v e balances, 2nd 5-day p e r i o d

Marked i n h i b i t i o n (51,74%) of non-heme i r o n absorption

fiber.


10.

BODWELL


on M i n e r a l u t i l i z a t i o n i n Humans.


Source

Fiber Intake

Mineral

Effect

Ref.

F r u i t s , 24g vegeNDF t a b l e s per day

Fe Ζη Cu

No e f f e c t Negative balances Negative balances

(27,28)

F r u i t s , 10,18 vege25g NDF t a b l e s per day

Zn

(29)

Cu

Lower balances on 25g f i b e r l e v e l No e f f e c t

10g per day

Zn

Negative balances

(30)

Cellu 14.2g lose, per day hemicellulose or p e c t i n

Zn

Lowered balances with h e m i c e l l u l o s e

(31)

Cellu10 o r 20g Zn u l o s e , per day hemicellulose or wheat bran

Increased f e c a l losses of zinc

(32)

Hemicellulose

Decreasing balances with increased f i b e r intake

(33)

Cellu lose

4.2,14.2, Zn 24.2g/day

14.7g/day Fe, Veget (basal) Zn arian diet plus cell ulose, 20g/day hemi cell ulose 20g/day or wheat bran 20g/day

F e c a l i r o n e x c r e t i o n (34,35) i n c r e a s e d with added h e m i c e l l u l o s e ; omnivores had decreased balances and v e g e t a r i a n s had l e s s p o s i t i v e balances with added c e l l u l o s e or h e m i c e l l u l o s e

Cellulose

Absorption not decreased

30-40 g/day

Zn

(36)


PLANT PROTEINS


Table I I .

E f f e c t s of P h y t i c

Molar ratio (phytic acid to zinc)

Source

Intake level of phytic acid

Wheat bran dephytinized

139mg/meal 9mg/meal

-

Soy

264mg/meal

-

protein

Acid

Meals with primary p r o t e i n from chicken + soy f l o u r beef + soy f l o u r soybeans

75mg/meal 200mg/meal 7mg/meal 200mg/meal 620mg/meal

D i e t s with 70% of p r o t e i n from textured soy soy i s o l a t e or animal p r o t e i n

3.8g/day 1.7g/day O.6g/day

Animal p r o t e i n d i e t Soy p r o t e i n d i e t

O.81g/day 1.38g/day

Sodium phytate

2.0g/meal

-

Sodium phytate (formula d i e t s )

2.34g/day

15

Sodium phytate (added t o bread)

~1.5g/day

.

Sodium phytate (in breads) Normal foods +Na Phytate +Na Phytate

a) C a l c u l a t e d

-

1

data.


a

a · a 24.4 l e 5 5

2

a

22.3 14.2 3.4

6

4

- a 9.6

a

1 3

a

-

O.5g/day 1.7g/day 2.9g/day

from a u t h o r s

13.4

4.7 16.3 27.5

10.

BODWELL


on Mineral U t i l i z a t i o n i n Humans.


Effect

Reference

Removal of o f 93% of p h y t i c a c i d d i d not improve absorption of non-heme i r o n

(24)

Removal of p h y t i c a c i d from soy d i d not improve non-heme i r o n a b s o r p t i o n

(38)

No e f f e c t s of p h y t i c a c i d on absorption; absorption depended on z i n c l e v e l

(39)

S i g n i f i c a n t l y decreased (40) i r o n balances with soy i s o l a t e d i e t ; tendency f o r z i n c balances t o decrease with increased phytic acid level Markedly decreased z i n c balances with soy d i e t

(41)

Iron a b s o r p t i o n decreased by 77%

(42)

Decreased z i n c a b s o r p t i o n by almost 50%

(36)

Zinc and i r o n balances not affected

(23)

Zinc absorptions 2 - f o l d higher (43) with low vs high phytate bread No e f f e c t on apparent a b s o r p t i o n of i r o n , manganese or copper; although not statistically significant, a b s o r p t i o n of z i n c tended to decrease with i n c r e a s e d phytic acid intake

(44)


PLANT PROTEINS


114

S i m p s o n e t a l . (24) d i d n o t o b s e r v e i n c r e a s e d non-heme i r o n a b s o r p t i o n when d e p h y t i n z e d b r a n was i n c l u d e d i n a t e s t meal compared t o t h e n o n - d e p h y t i n i z e d bran. Removal o f p h y t i c a c i d f r o m soy p r o t e i n l i k e w i s e d i d n o t i m p r o v e non-heme a b s o r p t i o n ( 3 8 ) . Decreased i r o n b a l a n c e s , o b s e r v e d by B o d w e l l e t a l . (40) w i t h soy i s o l a t e d i e t s , d i d n o t a p p e a r t o be a s s o c i a t e d w i t h t h e l e v e l of p h y t i c a c i d ; a tendency f o r z i n c balances to d e c r e a s e w i t h i n c r e a s e d p h y t i c a c i d was o b s e r v e d . However, e v e n w i t h a m o l a r p h y t i c a c i d t o z i n c r a t i o o f 2 2 . 3 , a v e r a g e b a l a n c e s were p o s i t i v e (Table I I ) . In c o n t r a s t , a t a much l o w e r l e v e l o f p h y t i c a c i d i n t a k e , C o s s a c k and P r a s a d (41) o b s e r v e d n e g a t i v e z i n c b a l a n c e s w i t h a soy p r o t e i n d i e t . I n t h e l a t t e r s t u d y , t h e soy p r o d u c t s were "washed' w i t h EDTA; t h e p o s s i b i l i t y e x i s t s t h a t some r e s i d u a l EDTA r e m a i n e d w h i c h c o u l d have affected mineral u t i l i z a t i o n . G i l l o o l y e t a l . (42) o b s e r v e d t h a t i r o n a b s o r p t i o n s were m a r k e d l y d e c r e a s e d by t h e a d d i t o n o f sodium p h y t a t e t o t e s t m e a l s w h i l e s i m i l a r l y marked d e c r e a s e s i n z i n c a b s o r p t i o n have b e e n o b s e r v e d ( 3 6 , 4 3 ; T a b l e I I ) . C o n t r a d i c t o r y r e s u l t s were r e c e n t l y r e p o r t e d (23,14). A d d i t i o n o f h i g h l e v e l s (1.5 t o 2 . 9 g / d a y ) o f sodium phytate d i d not s i g n i f i c a n t l y a f f e c t the apparent a b s o r p t i o n o f i r o n , manganese, c o p p e r o r z i n c . I t has g e n e r a l l y b e e n presumed and o b s e r v e d ( 3 6 , 4 2 , 4 3 ) , t h a t p u r i f i e d s o d i u m p h y t a t e had d e l e t e r i o u s e f f e c t s i n humans s i m i l a r t o t h o s e o b s e r v e d i n a n i m a l s t u d i e s w h i l e t h e e f f e c t s o f i n d i g e n o u s p h y t i c a c i d have been q u e s t i o n e d . Recent r e s u l t s (23,44; T a b l e II) i n d i c a t e t h a t even w i t h p u r i f i e d sodium p h y t a t e , d e l e t e r i o u s e f f e c t s a r e not always o b s e r v e d . The f o r m o f t h e p h y t i c a c i d - m i n e r a l - p r o t e i n complex p r e s e n t (12) may be t h e d e t e r m i n a n t f a c t o r as t o w h e t h e r a d e l e t e r i o u s e f f e c t is o b s e r v e d . 1

Protein

Source

The e f f e c t s o f p l a n t p r o t e i n s o u r c e s on i r o n and z i n c u t i l i z a t i o n have been o f p a r t i c u l a r c o n c e r n and t h e s u b j e c t o f t h e most s t u d i e s w i t h humans. Accordingly, t h e f o l l o w i n g d i s c u s s i o n is f o c u s e d on s t u d i e s c o n c e r n e d w i t h t h e s e two m i n e r a l s . Iron. In t h e human d i e t , two forms o f i r o n e x i s t , heme i r o n and non-heme i r o n ( 1 4 , 1 7 ) . i r o n is much more r e a d i l y a v a i l a b l e and a p p e a r s t o be a b s o r b e d by t h e human r e g a r d l e s s o f o t h e r components o f t h e d i e t w h i c h may i n h i b i t t h e a b s o r p t i o n o f t h e non-heme i r o n . However, i t has been e s t i m a t e d t h a t a b o u t 80% o f t h e d a i l y d i e t a r y i n t a k e o f i r o n is i n t h e f o r m o f non-heme i r o n and o n l y a b o u t 20% from heme i r o n . H e n c e , any p r o d u c t added t o t h e d i e t w h i c h c a u s e s a s i g n i f i c a n t d e c r e a s e i n non-heme i r o n a b s o r p t i o n is o f c o n c e r n . The b e l i e f t h a t soy p r o t e i n , added t o b e e f , c a u s e d a marked d e c r e a s e i n non-heme i r o n a b s o r p t i o n , l e d t o a H

e

m

e



10.

BODWELL


115

number o f s t u d i e s w h i c h a r e summarized i n T a b l e I I I . C o n t r a d i c t o r y r e s u l t s have b e e n o b t a i n e d ; h o w e v e r , t h i s c a n p a r t l y be e x p l a i n e d by more r e c e n t o b s e r v a t i o n s w h i c h w i l l be d i s c u s s e d b e l o w . In 3 s t u d i e s ( 4 5 - 4 7 ) , i n w h i c h men were f e d c o m p l e t e d i e t s f o r 10 t o 82 d a y s , a b s o r p t i o n s o f non-heme i r o n were s i m i l a r t o t h o s e o b s e r v e d w i t h m i l k - b a s e d d i e t s (45, 46) o r were m a i n t a i n e d a t an a d e q u a t e l e v e l ( 4 7 ) . However, i n t h e s e s t u d i e s an e x c e s s o f a s c o r b i c a c i d , w h i c h e n h a n c e s a b s o r p t i o n o f non-heme i r o n ( 1 7 ) , was p r o v i d e d . In a s t u d y i n w h i c h a more u s u a l l e v e l o f a s c o r b i c a c i d was p r o v i d e d , a soy i s o l a t e d i e t was o b s e r v e d t o r e s u l t i n s i g n i f i c a n t l y lower i r o n b a l a n c e s than t h o s e observed w i t h t e x t u r e d soy o r a n i m a l p r o t e i n d i e t s (40). In a s e r i e s o f s t u d i e s , Cook and c o - w o r k e r s ( 4 8 , 4 9 , 5 0 ) o b s e r v e d a marked d e c r e a s e i n non-heme i r o n a b s o r p t i o n when soy p r o t e i n was added t o b e e f o r p r o t e i n m i x t u r e s o r when soy p r o t e i n was consumed a s t h e p r i m a r y p r o t e i n s o u r c e i n t e s t meals and compared t o t h e e f f e c t s o f i n c l u d i n g egg albumen o r b e e f a l o n e i n t h e t e s t meal (Table I I I ) . H a l l b e r g and R o s s a n d e r ( 3 8 ) , h o w e v e r , f o u n d l e s s o f an e f f e c t when t o t a l i r o n a b s o r p t i o n (heme p l u s non-heme i r o n ) was c o n s i d e r e d . L i k e w i s e , i n a study i n w h i c h r e c o n s t i t u t e d t e x t u r e d s o y was u s e d t o r e p l a c e 30% o f t h e b e e f , t h e a b s o r p t i o n s o f t o t a l i r o n were n o t g r e a t l y a l t e r e d (51). I n a s t u d y by S t e k e l e t a l . (52), r e p l a c i n g p a r t o f the beef w i t h soy i s o l a t e o r a d d i n g h y d r a t e d i s o l a t e t o b e e f d e c r e a s e d non-heme i r o n a b s o r p t i o n f r o m 12.4% t o 9.2 and 9.3%, r e s p e c t i v e l y . In a r e l a t e d s t u d y , non-heme and t o t a l i r o n a b s o r p t i o n s were low when s o y i s o l a t e was t h e m a j o r p r o t e i n s o u r c e . In a s t u d y c o n d u c t e d a t B e l t s v i l l e , M o r r i s e t a l . (53) measured a b s o r p t i o n s i n men b e f o r e and a f t e r t h e y had consumed b e e f o r b e e f e x t e n d e d w i t h 6 d i f f e r e n t s o y p r o d u c t s ( T a b l e I I I ) as t h e i r p r i m a r y p r o t e i n s o u r c e i n 9 o f 14 b r e a k f a s t and e v e n i n g meals f o r 6 m o n t h s . No c o n s i s t e n t d i f f e r e n c e s o r c h a n g e s among t h e g r o u p s were observed. In t h e same B e l t s v i l l e s t u d y , no c h a n g e s i n c l i n i c a l p a r a m e t e r s o r i n serum f e r r i t i n l e v e l s were o b s e r v e d i n t h e men n o r i n t h e women and c h i l d r e n p a r t i c i p a t i n g and c o n s u m i n g b e e f p a t t i e s e x t e n d e d w i t h t h e v a r i o u s soy p r o d u c t s (54, 55). H a l l b e r g and R o s s a n d e r (38) f e d 9 o r 10 s u b j e c t s a b a s a l t e s t meal c o n t a i n i n g m a i z e , r i c e and b l a c k beans o r t h e same meal w i t h b e e f o r s o y f l o u r a d d e d . Non-heme i r o n a b s o r p t i o n s o f 3 . 2 , 8.4 and 4.8% and t o t a l i r o n a b s o r p t i o n s o f O.18, O.63 and O.51 mg were o b s e r v e d f o r t h e b a s a l m e a l , t h e b a s a l meal p l u s b e e f , and t h e b a s a l meal p l u s soy f l o u r , r e s p e c t i v e l y . The a u t h o r s c o n c l u d e d t h a t t h e amount o f i r o n a b s o r b e d was " s u b s t a n t i a l l y augmented" by t h e a d d i t i o n o f t h e s o y f l o u r w h i c h was h i g h i n i r o n .



studies

( s i n g l e meals)

Infant food supplements (corn, soy, whey and/or wheat p r o t e i n blends) given i n t e s t meals t o 3 o r 14 a d u l t men

Absorption

D i e t s based on textured soy, soy i s o l a t e o r animal p r o t e i n ; each d i e t f e d t o 16 o r 17 men f o r 35 days; 60mg a s c o r b i c acid/day

(complete d i e t s )

Non-heme i r o n a b s o r p t i o n s were low (O.57-1.40%) f o r soy c o n t a i n i n g mixtures

Balance values f o r soy i s o l a t e d i e t s s i g n i f i c a n t l y lower than values f o r t e x t u r e d soy or animal d i e t s

(48)

(40)

(47)

Non-heme i r o n a b s o r p t i o n of 13% (82 days)

S i x men f e d soy concentrate d i e t s f o r 82 days (7 12-day p e r i o d s ) ; 75mg a s c o b r i c a c i d consumed w i t h each meal

Balance s t u d i e s

(46)

Non-heme i r o n a b s o r p t i o n s (28-32%) e q u i v a l e n t

E i g h t men f e d DSM or soy p r o t e i n concentrate d i e t s , each f o r 10-day p e r i o d s ; 72mg a s c o b r i c a c i d consumed with each meal

Ref.

(45)


Results

E f f e c t s of Soy P r o t e i n on Iron U t i l i z a t i o n i n Humans.

Absorptions (17-21%) of non-heme i r o n among d i e t s were e q u i v a l e n t

studies

III.

F i v e men f e d d r i e d skim milk (DSM), DSM p l u s soy i s o l a t e o r soy i s o l a t e d i e t s , each f o r 14-day p e r i o d s ; "adequate" l e v e l s of a s c o r b i c a c i d provided

Absorption

Description

Table


Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986. (38)

Non-heme i r o n a b s o r p t i o n s of (a) 11.2, (b) 8.4, (c) 11.2, (d) 7.2 (e) 5.6, (f) 5.2 and (g) 5.2%; t o t a l i r o n (heme + non-heme) a b s o r p t i o n s o f (c) O.47mg, (d) O.33mg, and (e) O.28mg; i n (g), about 22.5% o f l a b e l l e d heme i r o n absorbed

S e r i e s of s t u d i e s w i t h test-meals i n which the major p r o t e i n sources were (g p r o t e i n and source): (a) 14g, beef, (b) 7g, beef, (c) 14g, beef, (d) 7g, beef + 7g, t e x t u r e d soy, (e) 7g, beef + 7g, soy f l o u r , (f) 7g, beef + 7g, d e p h y t i n i z e d soy f l o u r + l a b e l l e d hemoglobin; same s u b j e c t s o n l y w i t h i n 2 p a i r s of s t u d i e s (c-d, e-f)

(Continued)

(50)

Non-heme i r o n a b s o r p t i o n s o f (a) O.36, (b)1.44, (c)5.94, and (d)7.47%


S e m i - p u r i f i e d t e s t meals, f e d t o 7 men; contained (a) soy i s o l a t e , (b) soy i s o l a t e , + 100g beef, (c) egg albumen, o r (d) egg albumen + 100g beef

Absorption studies

Absorptions of non-heme i r o n were O.56 and 3.20, (soy i s o l a t e , i s o l a t e + a s c o r b i c a c i d ) , 5.05 and 10.19 (albumen, albumen + ascorbic acid)

Added 100 mg a s c o r b i c a c i d t o soy i s o l a t e or egg albumen s e m i p u r i f i e d t e s t meals; 9 a d u l t men

(50)

As measured by e x t r i n s i c r a d i o i r o n (49) l a b e l s , non-heme i r o n a b s o r p t i o n s were: Study I, (a) 2.49%, (b) 2.74, and (c) O.46%; i n Study I I , (a) 5.50, (b) O.97 (c) 1.91, and (d) O.41%; i n Study I I I (a) 3.20, (b) 1.24, (c) 1.51, and (b) 19.88%

In Study I, 15 men consumed s e m i - s y n t h e t i c meals w i t h (a) egg albumin, (b) c a s e i n , o r (c) i s o l a t e d soy p r o t e i n ; i n Study I I , semip u r i f i e d meals were f e d t o 10 men i n which p r o t e i n was from (a) egg albumen, (b) soy f l o u r , (c) t e x t u r e d soy f l o u r , o r (d) soy i s o l a t e ; i n Study I I I , 11 men consumed meals c o n t a i n i n g (a) 100g beef, (b) 100g beef p l u s 30g unrehydrated t e x t u r e d soy, (c) 70g beef p l u s 30g unrehydrated t e x t u r e d soy o r (d) r e f e r e n c e i r o n + a s c o r b i c a c i d


Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986. In Study I, a b s o r p t i o n s of non-heme i r o n o f (a) 12.4, (b) 9.2 and (c) 9.3. In Study I I , non-heme i r o n a b s o r p t i o n s of (a) 25, (b) 26.2, and (c) 2.1%; t o t a l i r o n (heme p l u s non-heme) a b s o r p t i o n s of (a) O.38, (b) O.22 and (c) O.05mg Among groups, mean i n i t i a l non-heme i r o n a b s o r p t i o n s v a r i e d from 2.4 t o 5.5%, mean f i n a l v a l u e s from 5.3 t o 7.6%; no c o n s i s t e n t d i f f e r e n c e s or changes among groups Non-heme i r o n a b s o r p t i o n s o f (a)3.2, (b)8.4, and (c)4.8; t o t a l i r o n a b s o r p t i o n s of (a) O.18, (b)O.63, (c)O.51 and (d)O.64mg. Soy product "sub s t a n t i a l l y augmented" the amount of non-heme i r o n absorbed from b a s a l meal

In Study I (28 s u b j e c t s ) , meals contained (a) 100g beef, (b) 100g beef p l u s 50g hydrated soy i s o l a t e , (c) 50g beef p l u s 50g hydrated soy i s o l a t e ; i n Study II (29 s u b j e c t s ) , meals contained (a) i n t r i n s i c a l l y l a b e l e d c h i c k e n , (b) soy i s o l a t e p l u s c h i c k e n , or (c) soy isolate

Absorptions measured i n men before and a f t e r consuming beef p a t t i e s (no soy p r o t e i n ) , or p a t t i e s extended (20% l e v e l ) with soy concen t r a t e , soy i s o l a t e o r t e x t u r e d soy (with or without f o r t i f i c a t i o n o f soy products with i r o n and zinc) f o r 9 o f 14 weekly morning and evening meals f o r 6 months.

Nine o r 10 s u b j e c t s f e d meal (a) b a s a l c o n t a i n i n g maize, r i c e , and black beans, or the b a s a l meal with (b) 75g beef added, (c) 15g soy f l o u r added, o r (d) i r o n ( f e r r o u s s u l f a t e ) added i n an amount e q u i v a l e n t t o t h a t provided by the soy f l o u r i n (c)

(51)

Ref.

(38)

(53)

(52)

(Continued).

Non-heme i r o n a b s o r p t i o n s o f (a) 3.2, (b) 1.2 and (c) 1.5%; t o t a l i r o n (heme p l u s non-heme) a b s o r p t i o n s of (a) O.44, (b) O.36, and (c) O.41mg

Results

E f f e c t s o f Soy P r o t e i n on Iron U t i l i z a t i o n i n Humans

Eleven men f e d meals c o n t a i n i n g (a) 100g beef, (b) 100g beef p l u s 30g r e c o n s t i t u t e d t e x t u r e d soy, or (c) 70g beef p l u s 30g soy product

Description

Table I I I .


m ζ

Η

Ο

Ό 73

Η

> ζ


10.

BODWELL

119


Some of the apparent d i s c r e p a n c i e s between s t u d i e s (often between s t u d i e s based on long-term f e e d i n g vs those i n v o l v i n g s i n g l e t e s t meals) can, i n p a r t , be explained by the r e s u l t s of a recent study by Lynch e t al. (56). In t h i s study, the heme-iron and the non-heme i r o n were s e p a r a t e l y l a b e l e d with d i f f e r e n t i r o n i s o t o p e s . The a d d i t i o n of soy p r o t e i n to beef caused a marked decrease i n non-heme i r o n a b s o r p t i o n ( 5 . 1 vs 1 . 9 % ) . However, a marked i n c r e a s e was observed i n the a b s o r p t i o n of the heme i r o n upon i n c l u s i o n of the soy p r o t e i n (increased from 3 3 . 1 to 4 2 . 1 % ) . The amount of t o t a l i r o n absorbed was decreased by the i n c l u s i o n of soy ( O . 4 3 mg i n s t e a d of O.56 mg); however, the decrease was not as marked as would have been suggested by the r e s u l t s of the e a r l i e r s t u d i e s and might not be d e l e t e r i o u s during long-term consumption. Lynch e t a l . (5J7) found non-heme i r o n a b s o r p t i o n s , as measured by s i n g l e t e s t meals, f o r black beans, l e n t i l s , mung beans s p l i t peas, and whole soybeans to be low ( O . 8 4 to 1 . 9 1 % ) . T h i s suggests that many commonly consumed legumes are poor sources of i r o n ; whether legumes other than soy may have an " o f f s e t t i n g enhancing e f f e c t on heme-iron a b s o r p t i o n cannot be predicted. Z i n c . Some recent s t u d i e s on the e f f e c t s of soy p r o t e i n on z i n c u t i l i z a t o n are summarized i n Table IV. Young and Janghorbani (4j4) and I s t f a n et a l . (46) compared the e f f e c t s of soy i s o l a t e or soy concentrate and d r i e d skim milk as p r o t e i n sources i n multi-day feeding p e r i o d s . Zinc a b s o r p t i o n s , measured by f e c a l monitoring of the e x t r i n s i c l a b e l g i v e n , were e q u i v a l e n t and no d e l e t e r i o u s e f f e c t s of soy p r o t e i n were observed. In a second study, I s t f a n e t a l . (47) fed egg p r o t e i n d i e t s f o r 10 days and then a soy concentrate d i e t f o r 82 days. Zinc absorptions were not decreased by feeding the soy concentrate d i e t . Sandstrom and Cederblad (39) fed s i n g l e t e s t meals of chicken, beef, chicken or beef plus soy f l o u r or soybeans. The amount of z i n c i n the t e s t meal a f f e c t e d a b s o r p t i o n (Table IV) but not soy f l o u r per se. Higher l e v e l s of z i n c r e s u l t e d i n lowered a b s o r p t i o n s . Janghorbani e t a l . ( 5 8 ) fed i s o n i t r o g e n o u s d i e t s to 10 s u b j e c t s f o r 12 days. Both an i n t r i n s i c l a b e l (chicken) and e x t r i n s i c l a b e l s were used. Zinc absorptions from an a l l - c h i c k e n d i e t and from a 50% c h i c k e n - 5 0 % soy i s o l a t e d i e t were e q u i v a l e n t . Solomons et a l . (59) fed 5 or 10 s u b j e c t s d i e t s i n which milk, soy i s o l a t e , and beef (or mixtures of these) were p r o t e i n sources; f o r the milk and/or soy d i e t s , absorptions were s i m i l a r ; " f r a c t i o n a l " absorptions from beef bologna may have been higher than from soy bologna (Table IV). In the a b s o r p t i o n study conducted by I s t f a n e t a l . (47), z i n c balances were a l s o determined. Mean z i n c balances were p o s i t i v e and serum z i n c l e v e l s were w


Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986. f

(46)

(47)

(39)

Zinc a b s o r p t i o n s were e q u i v a l e n t ; mean values o f (a)29 and (b)26% Zinc a b s o r p t i o n s not d i f f e r e n t ; mean values of (a)31% and (b) 23%; f o r seven 12-day p e r i o d s of soy d i e t , mean values v a r i e d from 19 t o 32% Absorptions were (a) 36.2, (b) 20.4, (c) 24.7, (d) 16.5, (e) 19.6, (f) 24.4, and (g) 15.3%; a b s o r p t i o n appeared t o depend on zinc intake level

Six s u b j e c t s f e d formula d i e t s w i t h p r o t e i n provided by (a) egg (10 days) o r soy concen t r a t e (82 days); e x t r i n s i c z i n c l a b e l ( f e c a l monitoring method)

Six t o 11 s u b j e c t s consumed i s o n i t r o g e n o u s t e s t meals with primary p r o t e i n source being (a) c h i c k e n , (b) beef, (c) c h i c k e n + soy f l o u r , (d) beef + soy f l o u r , (e) soybeans, (f) chicken + z i n c , (g) beef + z i n c ; e x t r i n s i c z i n c l a b e l (whole body r e t e n t i o n measured)

(44)

Ref.

E i g h t s u b j e c t s f e d (10 days) formula d i e t s with e i t h e r (a) DSM o r (b) soy p r o t e i n concen t r a t e as p r o t e i n source; e x t r i n s i c z i n c l a b e l ( f e c a l monitoring method)

Absorptions (37-41%) e q u i v a l e n t among 3 d i e t s

Results

E f f e c t s of Soy P r o t e i n on Zinc U t i l i z a t i o n i n Humans.

F i v e s u b j e c t s consumed (14 days) formula d i e t s with p r o t e i n provided from e i t h e r (a) d r i e d skim milk (DSM) (b) DSM + soy i s o l a t e (50:50 p r o t e i n b a s i s ) , o r (c) soy i s o l a t e ; e x t r i n s i c z i n c l a b e l ( f e c a l monitoring method)

Absorption S t u d i e s

Description

Table IV.


c/3

ζ

70

Ο Η m

Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986. Mean z i n c balances v a r i e d (+O.14 t o +1.38mg/day) f o r 7 12-day balances; serum z i n c l e v e l s constant a c r o s s 82 days Mean balances f o r days 15-21 not d i f f e r e n t ; although p o s i t i v e , mean balances f o r days 29-35 were lower f o r (a) and (b) compared to (c) Mean z i n c balances lower and n e g a t i v e , -2.39mg/day f o r (b); +3.25mg/day f o r (a); plasma z i n c l e v e l s lower f o r (b); p o s s i b l y d e l e t e r i o u s e f f e c t s of " r e s i d u a l " EDTA a p p a r e n t l y not determined

Subjects (16 or 17) consumed meals w i t h >70% of p r o t e i n from (a) t e x t u r e d soy, (b) soy i s o l a t e or (c) animal p r o t e i n sources, each f o r 35 days

F i v e s u b j e c t s consumed (a) animal p r o t e i n d i e t or (b) soy p r o t e i n ( f l o u r , i s o l a t e ) d i e t f o r 3 months; soy products "washed" with EDTA

Studies

Mean a b s o r p t i o n s were (a) 41, (b) 34, (c) 41, (d) 30 and (e) 41%; no d i f f e r e n c e s between ( a ) , (b), ( c ) ; (e) may have "favored z i n c a b s o r p t i o n " over (d).

Absorptions of z i n c e q u i v a l e n t between d i e t s w i t h s i m i l a r z i n c i n t a k e s ; a b s o r p t i o n s higher with low z i n c i n t a k e

Six s u b j e c t s f e d formula d i e t s w i t h p r o t e i n provided by soy concentrate (82 days)

Balance

f

F i v e or 10 s u b j e c t s f e d (12-14 days) d i e t s with (a) nonfat d r i e d m i l k (b) soy i s o l a t e , (c) milk & i s o l a t e , (d) soy i s o l a t e bologna and (e) beef bologna; e x t r i n s i c z i n c l a b e l s used ( f e c a l monitoring method)

Ten s u b j e c t s fed (12 days) i s o n i t r o g e n o u s d i e t s w i t h a l l p r o t e i n from c h i c k e n meat or 50% from c h i c k e n and 50% from soy i s o l a t e ; i n t r i n s i c (chicken) and e x t r i n s i c l a b e l s used ( f e c a l monitoring method)


(41)

(40)

(47)

(59)

(58)

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PLANT PROTEINS


unchanged across the 82-day p e r i o d of feeding soy concentrate. In the study by Bodwell e t a l . (40) mean balances were lower f o r textured soy and soy i s o l a t e d i e t s , compared to an animal p r o t e i n d i e t , but were s t i l l p o s i t i v e . Conversely, Cossack and Prasad (41) observed negative balances when a d i e t c o n t a i n i n g soy i s o l a t e plus textured soy was fed f o r 3 months. However, as noted above, whether or not the EDTA used to "wash" the soy products was completely removed is unknown. Reasons f o r Discrepancies As noted above, disagreement has o f t e n been observed among d i f f e r e n t s t u d i e s on the e f f e c t s of f i b e r , p h y t i c a c i d and p r o t e i n source on mineral u t i l i z a t i o n . Some p o s s i b l e reasons i n c l u d e : (a) estimates of absorption from s i n g l e meals (with or without previous consumption of the same foods used i n the t e s t meal which may also a f f e c t r e s u l t s ) may not always be e q u i v a l e n t to r e s u l t s from multi-day balance s t u d i e s , (b) i n balance s t u d i e s , the f a i l u r e to allow s u f f i c i e n t time (e.g., 1-2 weeks or more) f o r adaptation may a l t e r the f i n d i n g s , (c) v a r i a t i o n s i n the compositions of meals or d i e t s , i n c l u d i n g mineral l e v e l s , between s t u d i e s may i n f l u e n c e the r e s u l t s obtained, and (d) the persons used as subjects vary and t h i s may have an a f f e c t . In a d d i t i o n , i n the f i b e r s t u d i e s , the l e v e l s , types, and p a r t i c l e s i z e of f i b e r fed have v a r i e d widely and l e v e l s of other p o s s i b l y confounding components (e.g., c a f f e i n e , t a n i n s , oxalates) may have d i f f e r e d . P r a c t i c a l Implications Numerous s t u d i e s (e.g., 60-63) have evaluated the n u t r i t i o n a l mineral status of v e g e t a r i a n s . Most consume r e l a t i v e l y high l e v e l s of f i b e r and some probably consume a r e l a t i v e l y high l e v e l of p h y t i c a c i d . Although exceptions occur, i n general t h e i r mineral s t a t u s has been adequate. Obviously, adaptation occurs; t h i s has been shown c l i n i c a l l y (34,35). I t thus seems u n l i k e l y that increased intakes of vegetable p r o t e i n products pose long term r i s k s f o r those accustomed to non-vegetarian d i e t s . Literature Cited 1. 2. 3. 4. 5.

Berner, L.A. and M i l l e r , D.D. JAOCS (In P r e s s ) . Sandstead, H.H. Am. J . C l i n Nutr. 1982, 35, 809. Morck, T.A. and Cook, J.D. Cereal Foods World 1981, 260, 667. Kelsay, J.L. Cereal Chem. 1981, 58, 2. Kelsay, J.L. Am. J . Clin. Nutr., 1978, 31, 142.


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6. 7.

8. 9.


10.

11. 12. 13. 14.

15. 16. 17. 18. 19. 20.

21. 22. 23. 24. 25. 26. 27.


Bodwell, C.E. Cereal Foods World, 1983, 23, 343. Bodwell, C.E. and Hopkins, D.T. In "New P r o t e i n Foods, V o l . 5, Seed Storage P r o t e i n s " ( A l t s c h u l , A.M., and Wilcke, H.L., Eds.), Academic Press, N.Y., (1985) pp. 221-257. Solomons, N.W. Am. J . Clin. Nutr. 1982, 35, 1048. Davies, N.T. In "Dietary F i b e r In Health and Disease" (Vahouny, G.V., and Kritchevsky, D., Eds.), Plenum Pres, N.Y., 1982, pp. 105-116. Smith, J.C., J r . , M o r r i s , E.R. and Ellis, R. In "Zinc D e f i c i e n c y In Human Subjects" ( Prasad, A.S. Cabdar, A.O., Brewer, G.J., Aggett, P.J., Eds.), A.L. L i s s , N.Y, 1983, pp. 147-169. Erdman, J.W., J r . Cereal Chem. 1981, 58, 21. Erdman, J.W., J r . and Forbes, R.M. JAOCS 1981, 58, 489. Turnland, J.R. Cereal Foods World, 1982, 27, 152. Bothwell, T.H., Clydesdale, F.M., Cook, J.D., Dallman, P.R., H a l l b e r g , L., Van Campen, D. and Wolf, W.J. "The E f f e c t s of Cereals and Legumes on Iron Availability," I n t e r n a t l . N u t r i t i o n a l Anemia C o n s u l t a t i v e Group, The N u t r i t i o n Foundation, Washington, D.C., 44 pages, 1982. Kies, C. (Ed.) " N u t r i t i o n a l B i o a v a i l a b i l i t y of Iron", ACS SYMPOSIUM SERIES 203, American Chemical S o c i e t y , Washington, D.C., 1982. I n g l e t t , G.E. (Ed). " N u t r i t i o n a l B i o a v a i l a b i l i t y of Z i n c , " ACS SYMPOSIUM SERIES 210, American Chemical S o c i e t y , Washington, D.C., 1983. Monsen, E.R., H a l l b e r g , L., L a y r i s s e , M., Hegsted, D.M., Cook, J.D., Mertz, W., and F i n c h , C.A. Am. J . Clin. Nutr. 1978, 31, 134. Reinhold, J.G. In Reference 15, pp. 143-161. Guthrie, B.E. and Robinson, M.F. Fed. Proc. 1978, 37, 254. Sandstead, H.H., Munoz, J.M. Jacob, R.A., Klevay, L.M., Reck, S.J., Logan, G.M., J r . , D i n t z i s , F.R., I n g l e t t , G.E., and Shuey, W.C. Am. J . Clin. Nutr. 1978, 31, S180. M o r r i s , E.R. and Ellis, R. In Reference 15, pp. 121-141. M o r r i s , E.R. and Ellis, R. In Reference 16, pp. 159-172. Andersson, Η., Navert, Β., Bingham, S.A., Englyst, H.N. and Cummings, J.H. Br. J . Nutr. 1983, 50, 503. Simpson, K.M., M o r r i s , E.R. and Cook, J.D. Am. J . Clin. Nutr. 1981, 34, 1469. Sandberg, A.-S., Hasselblad, C. and Hasselblad, K. J. Nutr. 1982, 48, 185. Van Dokkum, W., Wesstra, A. and Schippers, F.A. Br. J . Nutr. 1982, 47, 451. Kelsay, J.L., B e h a l l , K.M., and Prather, E.S. Am. J . Clin. Nutr. 1979, 32, 1876.


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28. Kelsay, J.L., Jacob, R.A., and Prather, E.S. Am. J. Cln. Nutr. 1979, 32, 2307. 29. Kelsay, J.L., C l a r k , W.M., Herbst, B.J., and Prather, E.S., Fed. Proc. 1979, 38, 767. 30. I s m a i l - B e i g i , F., Reinhold, J.G., F a r a d j i , B., and Abadi, P., J. Nutr. 1977, 107, 510. 31. Drews, L.M., K i e s , C., and Fox, H.M., Am. J. Clin. Nutr. 1979, 32, 1893. 32. Papakyrikos, H., Kies, C., and Fox, H.M., Fed. Proc. 1979, 38, 549. 33. Kies, C., Fox, H.M., and Beshgetoor, D., Cereal Chem. 1979, 56, 133. 34. Kies, C., Young, E. and McEndree, L. In Reference 16, pp. 8-126. 35. Kies, C. and McEndree, L. In Refernce 16, pp. 183-198. 36. Turnland, J.R., King, J.C., Keyes, W.R., Gong, B. and M i c h e l , M.C. Am. J. Clin. Nutr. 1984, 40, 1071. 37. Kelsay, J.J. In Reference 16, pp. 127-143. 38. H a l l b e r g , L. and Rossander, L. Am. J. Clin. Nutr. 1982, 36, 514. 39. Sandstrom, B. and Cederblad, A. Am. J. Clin. Nutr. 1980, 33, 1778. 40. Bodwell, C.E., Smith, J.C., Judd, J., S t e e l e , P.D., Cottrell, S.L., Schuster, E., S t a p l e s , R., XII I n t e r n a t i o n a l N u t r i t i o n Congress, (Abstr), San Diego, CA (1981). 41. Cossack, Ζ.T. and Prasad, A.S. Nutr. Res. 1983, 3, 23. 42. G i l l o o l y , M., Bothwell, T.H., Torrance, J.D., MacPhail, A.P., Derman, D.P., Bezwoda, W.R., M i l l s , W. and C a r l t o n , R.W. Br. J. Nutr. 1983, 49, 331. 43. Navert, Β., Cedarblad, A. and Sandstrom, B. In Reference 25. 44. M o r r i s , E.R. and Ellis, R. 1986. In "Trace Element Metabolism In Man And Animals-IV." ( M i l l s , C.F., Aggett, P.J., Bremner, I . , Chesters, J.K., Eds.) Cambridge U n i v e r s i t y Press, London, 1986 (In Press). 45. Young, V.R., and Janghorbani, M. (1981). C e r e a l Chem. 1981, 58, 12. 46. I s t f a n , Ν., Murray, E., Janghorbani, M., and Young, V.R. J. Nutr. 1983, 113, 2516. 47. I s t f a n , Ν., Murray, Ε., Janghorbani, M., Evans, W.J., and Young, V.R. J. Nutr. 1983, 113, 2524. 48. Morck, T.A., Lynch, S.R., and Cook, J.D. Am. J. Clin. Nutr. 1981, 34, 2630. 49. Cook, J.D., Morck, T.A., and Lynch, S.R. Am. J. Clin. Nutr. 1981, 34, 2622. 50. Morck, T.A., Lynch, S.R., and Cook, J.D. Am. J. Clin. Nutr. 1981, 36, 219. 51. Cook, J. Data p u b l i s h e d in Reference 14.



10. BODWELL


52. S t e k e l , A. Data p u b l i s h e d in Reference 14. 53. M o r r i s , E.R., Bodwell, C.E., M i l e s , C.W., Mertz, W., Prather, E.S., and Canary, J.J. Fed. Proc. 1983, 42, 530. 54. M i l e s , C.W., Bodwell, C.E., M o r r i s , E.R., Mertz, W., Canary, J.J., Prather, E.S., Fed. Proc. 1983, 42, 529. 55. Bodwell, C.E., M i l e s , C.W., M o r r i s , E.R., Mertz, W., Canary, J.J., and Prather, E.S., Fed. Proc. (1983) 42:529. 56. Lynch, S.R., Dassenko, S.A., Morck, T.A., Beard, J.L., and Cook, J.D. Am. J. Clin. Nutr. 1985, 41, 13. 57. Lynch, S.R., Beard, J.L., Dassenko, S.A. and Cook, J.D. Am. J. Clin. Nutr. 1984, 40, 42. 58. Janghorbani, M., I s t f a n , N.W., Pagounes, J.O., Steinke, F.H., and Young, V.R. Am. J. Clin. Nutr. 1982, 36, 537. 59. Solomons, N.W., Janghorbani, Μ., T i n g , B.T.G., Steinke, F.H., C h r i s t e n s e n , Μ., Bijlani, R., I s t f a n , N. and Young, V.R. J. Nutr. 1982, 112, 1809. 60. Anderson, B.M., Gibson, R.S. and Sabry, J.H. Am. J. Clin. Nutr. 1981, 34, 1042. 61. Harland, B.F. and Peterson, M. J. Am. D i e t e t . A. 1978, 72, 259. 62. Dwyer, J.T., D i e t z , W.H., J r . , Andrews, E.M. and Suskind, R.M. Am. J. Clin. Nutr. 1982, 35, 204. 63. S c h u l t z , T.D. and Leklem, J.E., J. Am. D i e t e t . A. 1983, 83, 27. RECEIVED March 17, 1986


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