Vegetarianism and the Bioavailability of Iron - ACS Symposium Series

12 Vegetarianism and the Bioavailability of Iron C. KIES and L. McENDREE

Downloaded by RUTGERS UNIV on February 22, 2016 | http://pubs.acs.org Publication Date: November 1, 1982 | doi: 10.1021/bk-1982-0203.ch012

University of Nebraska, Lincoln, NB 68583

Increasing the proportion of plant to animal products in diets should have profound effects on the iron nutritional status of human populations. Such diets tend to be lower in heme iron, higher in fiber, and higher in phytates, a l l factors which inhibit utilization of iron. In addition, i t is thought that vegetarian diets tend to be low in total iron. However, in a laboratory controlled study, vegetarians were found to better utilize iron from a vegetarian diet than were omnivores consuming the same vegetarian diet. These results support the theory that iron absorption is in part mediated by the nutritional needs of the host. E i t h e r because of economic n e c e s s i t y or because of choice based on e t h i c a l , h e a l t h o r r e l i g i o u s c o n s i d e r a t i o n s , many Americans a r e i n c r e a s i n g the c e r e a l / v e g e t a b l e / f r u i t components of t h e i r d i e t s while decreasing the animal product components. The U.S. D i e t a r y Goals would seem t o suggest that t h i s i s d e s i r a b l e . While the numbers of i n d i v i d u a l s adopting frank vegetarianism are r e l a t i v e l y few, s h i f t s i n food i n t a k e p a t t e r n s may r e s u l t i n a c t u a l s h i f t s of n u t r i e n t i n t a k e s or i n s h i f t s i n n u t r i e n t to n u t r i e n t enhancer p a t t e r n s or i n n u t r i e n t to n u t r i e n t i n h i b i t o r p a t t e r n s . By examining n u t r i t i o n a l w e l l - b e i n g of veget a r i a n s , i t may be p o s s i b l e t o gain i n s i g h t s on the f u t u r e n u t r i t i o n a l s i t u a t i o n s of i n d i v i d u a l s who a r e merely s h i f t i n g p r o p o r t i o n s o f b a s i c foods w i t h i n t h e i r d i e t s so as t o i n c r e a s e the p l a n t product components and to decrease the animal product components. The a b i l i t y of p l a n t - o r i e n t e d d i e t to provide f o r adequacy of i r o n n u t r i t i o n has been questioned both i n terms o f t o t a l i r o n provided by these d i e t s and i n terms of the a v a i l a b i l i t y of i r o n from plant-based products. T h i s paper w i l l address both of these i s s u e s .

0097-6156/82/0203-0183$06.00/0 © 1982 American Chemical Society

In Nutritional Bioavailability of Iron; Kies, Constance; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

184

NUTRITIONAL BIOAVAILABILITY OF IRON


F a c t o r s A f f e c t i n g Iron Absorption from Vegetarian D i e t s In monogastric species i r o n a b s o r p t i o n takes p l a c e p r i m a r i l y i n the upper small i n t e s t i n e ( 1 ) . Not a l l the i r o n present i n foods i s absorbed i n t o the body. In the normal a d u l t with adequate s t o r e s of i r o n , u s u a l l y l e s s than 10% of the i r o n i n foods i s absorbed (2). Because of the body's l i m i t e d c a p a c i t y to excrete i r o n , the a b i l i t y to r e f r a i n from absorbing unneeded i r o n i s r e g u l a t e d i n the duodenum and i s r e f e r r e d to as the mucosal block (1). When the requirement f o r i r o n i n c r e a s e s as i n growth and pregnancy and i n v a r i o u s disease and d e f i c i e n c y s t a t e s , the mucosal block i s modified and increased i r o n absorpt i o n occurs. The explanation o f f e r e d by Underwood (3) i s as f o l l o w s : i r o n taken i n t o the mucosal c e l l i s converted to f e r r i t i n and when the c e l l s become p h y s i o l o g i c a l l y saturated with f e r r i t i n , f u r t h e r a b s o r p t i o n i s impeded u n t i l the i r o n i s r e l e a s e d from f e r r i t i n and t r a n s f e r r e d to plasma. The mechanism of the gut's i n f l u e n c e on i r o n a v a i l a b i l i t y i s the subject of much controversy. Researchers can be d i v i d e d i n t o two groups, one h o l d i n g that the i n t e s t i n e c o n t r o l s the absorpt i o n of i r o n by a l t e r i n g the mucosal a v i d i t y f o r i r o n , the other h o l d i n g that the contents of the lumen are changed to make the i r o n more or l e s s a v a i l a b l e according to requirement (1). I t i s w e l l e s t a b l i s h e d that the form of i r o n i n food a l s o a f f e c t s i t s a v a i l a b i l i t y f o r a b s o r p t i o n . Inorganic forms of i r o n and i r o n - p r o t e i n compounds need to be reduced to the f e r r o u s s t a t e and r e l e a s e d from conjugation f o r e f f e c t i v e a b s o r p t i o n ( 3 ) . Since most food i r o n i s i n the form of f e r r i c (Fe+4+) s a l t s , these must be reduced to be e f f i c i e n t l y absorbed ( 2 ) . S i m i l a r l y , f e r r o u s (Fe++) s a l t s are used p r e f e r e n t i a l l y to f e r r i c s a l t s i n the treatment of i r o n d e f i c i e n c i e s ( 1 ) . There has been much c o n s i d e r a t i o n of the e f f i c i e n c y of the a b s o r p t i o n of i r o n from foods of animal and p l a n t o r i g i n . Studies i n normal i n d i v i d u a l s on i r o n absorption from a s i n g l e food have shown that the mean i r o n absorption from vegetable foods ranged from 3 to 8% and from animal products from 8 to 16% (4). To determine the e f f e c t of vegetable and animal products on i r o n a b s o r p t i o n from f e r r i t i n , L a y r i s s e et a l . (5) s t u d i e d i r o n a b s o r p t i o n from f e r r i t i n b i o s y n t h e t i c a l l y l a b e l l e d with r a d i o i r o n i n 108 s u b j e c t s . The a d m i n i s t r a t i o n of t h i s i r o n compound together with vegetables i n a meal r e s u l t e d i n markedly lower l e v e l s of absorption than occurred from maize, wheat or soybeans. Iron absorption from f e r r i t i n was markedly increased when i t was administered with meat, but the absorption from the combination was only about one-half the amount absorbed from meat alone ( 5 ) . I t i s d i f f i c u l t to determine the reasons f o r decreased a b s o r p t i o n of vegetable i r o n sources; however, some researchers speculate that the f e r r i t i n administered with vegetable sources i s incomp l e t e l y m i s c i b l e with a nonheme i r o n p o o l or that i t a c t u a l l y forms a separate i r o n pool (3,5).



12.

KIES AND MCENDREE

Vegetarianism

185

Many f a c t o r s have been i d e n t i f i e d as i n f l u e n c i n g the absorpt i o n of i r o n . In a d d i t i o n to changes w i t h i n the host which a f f e c t i r o n absorption and the form of the i r o n s a l t , v a r i o u s d i e t a r y c o n s t i t u e n t s which may i n c r e a s e or decrease i r o n b i o a v a i l a b i l i t y have a l s o been s t u d i e d . As d i e t s become more p l a n t product o r i e n t e d and l e s s i r o n i s provided by animal products, the occurrence of these other d i e t a r y f a c t o r s i s a l s o l i k e l y to change. F a c t o r s which have been i m p l i c a t e d i n c l u d e the f o l l o w i n g : amount of heme i r o n , a s c o r b i c a c i d l e v e l , d i e t a r y p r o t e i n , d i e t a r y phytate, i r o n - m i n e r a l i n t e r a c t i o n s and l e v e l of d i e t a r y fiber. Heme i r o n from hemoglobin and myoglobin i s found only i n animal f l e s h products. Considerable research i n d i c a t e s that heme i r o n i s b e t t e r u t i l i z e d than i s non-heme i r o n as summarized by Monsen et a l . (6). Thus, a s h i f t i n d i e t s toward vegetarianism would be expected to decrease the p r o p o r t i o n of d i e t a r y i r o n provided by heme, thus decreasing i r o n a v a i l a b i l i t y . Limited evidence e x i s t s i n d i c a t i n g that not only i s heme i r o n b e t t e r u t i l i z e d than i s non-heme i r o n , but that heme i r o n i t s e l f i n creased u t i l i z a t i o n of non-heme i r o n (7-10). L e v e l of a s c o r b i c a c i d i n the d i e t has been found to be an important f a c t o r i n determining non-heme i r o n absorption (6,10,11). A s c o r b i c a c i d intake has been found to be more c l o s e l y c o r r e l a t e d to s e v e r a l biochemical parameters of i r o n n u t r i t i o n a l s t a t u s than was t o t a l i r o n intake (12). However, timing of consumption i s e q u a l l y important. I f non-heme i r o n absorption i s to be increased v i a t h i s f a c t o r , then both the non-heme i r o n and the a s c o r b i c a c i d must be consumed at the same time. Considering that important sources of a s c o r b i c a c i d are a l l of p l a n t o r i g i n , the chances that a s h i f t from more animal-based foods to more p l a n t based foods w i l l l e a d to increased consumption of a s c o r b i c a c i d are good indeed. However, t h i s i s not n e c e s s a r i l y the case i f the s h i f t moves toward a d i e t based s o l e l y , f o r example, on highly polished cereals. Phytate-bound i r o n may or may not c o n s t i t u t e a v a i l a b l e forms of i r o n to the human as discussed i n s e v e r a l other chapters of t h i s book. E a r l i e r work sugests that phytates i n h i b i t i r o n absorption. Since phytates and oxalates are provided by c e r e a l / p l a n t products, an increase i n the p l a n t components of d i e t i s l i k e l y to i n c r e a s e the i n t a k e of these i n h i b i t o r s . Several amino a c i d s are speculated to be e f f e c t i v e i n i n c r e a s i n g i r o n absorption and can be d i v i d e d i n t o three c a t e g o r i e s . These are 1) amino a c i d s which act as b u f f e r i n g agents i n the i n t e s t i n e and delay the increase of the pH towards n e u t r a l i t y where i r o n i s o x i d i z e d and forms i n s o l u b l e p r e c i p i t a t e s ; 2) amino a c i d s which form iron-amine c h e l a t e s that act to enhance i r o n absorption and; 3) amino a c i d s which act to stimul a t e i r o n t r a n s p o r t systems w i t h i n the animal (3). A wide v a r i e t y of soy products ranging from soy meal to soy p r o t e i n i s o l a t e s were found to have a strong i n h i b i t o r y e f f e c t on



186


non-heme i r o n .absorption (13). I t i s unknown whether the phytate content o f these products, the soy p r o t e i n i t s e l f , o r some other aspect r e l a t e d t o these products i s accountable f o r t h i s effect. I n t e r a c t i o n s among m i n e r a l s a f f e c t i n g t h e i r u t i l i z a t i o n a r e c u r r e n t l y an area o f i n t e n s e i n v e s t i g a t i o n . Greger has reviewed impacts o f phosphorus and c a l c i u m on i r o n u t i l i z a t i o n i n t h i s book. I n t e r a c t i o n s o f i r o n w i t h copper and z i n c have a l s o been e s t a b l i s h e d (14-16). I f m i n e r a l s compete w i t h i r o n f o r absorpt i o n b i n d i n g s i t e s , adverse e f f e c t s on i r o n b i o a v a i l a b i l i t y may occur. Since d i e t a r y f i b e r i s provided o n l y by plant-based products, i t i s reasonable t o suppose that as the animal product components of d i e t s a r e decreased and the p l a n t product components i n c r e a s e that d i e t a r y f i b e r i n t a k e w i l l be p r o p o r t i o n a l l y i n c r e a s e d . T h i s i s , however, dependent upon the k i n d o f p l a n t products which a r e i n c o r p o r a t e d . Studies designed t o study e f f e c t s o f d i e t a r y f i b e r on i r o n u t i l i z a t i o n have given mixed r e s u l t s . Kelsay e t a l . (17) reported no s i g n i f i c a n t e f f e c t of f i b e r from f r u i t s and vegetables on i r o n balances of young men. S i m i l a r r e s u l t s were r e p o r t e d by Sandstead e t a l . (18) when wheat bran was the d i e t a r y f i b e r source. Contrary t o t h i s , Reinhold e t a l . (19) found that dephytinized wheat and corn bran had an adverse e f f e c t on i r o n u t i l i z a t i o n . R e s u l t s from t h i s l a b o r a t o r y suggest that source of d i e t a r y f i b e r may be an important f a c t o r . In our s t u d i e s , h e m i c e l l u l o s e from p s y l l i u m and wheat bran i n h i b i t e d i r o n absorpt i o n , r i c e bran and c e l l u l o s e had a l e s s e r e f f e c t and no e f f e c t was determined when corn bran o r p e c t i n were the f i b e r source used (20-23). Iron Content of Vegetarian D i e t s I t has long been known that percent i r o n a b s o r p t i o n i s somewhat dependent upon the t o t a l amount of i r o n provided by the diet. S h i f t s i n consumption p a t t e r n s toward the e a t i n g of l e s s red meats may r e s u l t i n a c t u a l i n c r e a s e s i n t o t a l i r o n contents* of such d i e t a r i e s i f replacement i s made w i t h whole-grain o r enriched c e r e a l s ; however, i f the replacement i s i n terms of m i l k or cheese, as i s o f t e n the case w i t h the l a c t o - v e g e t a r i a n , the i r o n consumption may w e l l decrease. C a l c u l a t i o n s of i r o n i n t a k e s u f f i c i e n c y have been r e p o r t e d i n s e v e r a l papers. Iron i n t a k e s of 97 a d u l t omnivores (eaters of both p l a n t and animal p r o d u c t s ) , f i s h e a t e r s (eaters of p l a n t products but no f l e s h foods except f i s h ) , and v e g e t a r i a n s l i v i n g i n Maine were c a l c u l a t e d from 3-day d i e t a r y d i a r i e s and compared to the 1974 N a t i o n a l Research C o u n c i l Recommended D i e t a r y Allowances (NRC RDA's) f o r i r o n (24,25). Intakes of s e v e r a l other n u t r i e n t s were compared i n a s i m i l a r f a s h i o n . Of the male omnivores, f i s h e a t e r s and v e g e t a r i a n s , 88, 88, and 87%, r e s p e c t i v e l y , had i r o n i n t a k e s which met or exceeded 100% of the NRC


12.

KIES AND MCENDREE

Vegetarianism

RDA's f o r men. However, o f the female omnivores, f i s h e a t e r s , or v e g e t a r i a n s , only 4, 36, and 46%, r e s p e c t i v e l y , met o r exceeded the NRC RDA s f o r women; furthermore, 58, 45, and 8% of these three groups f a i l e d to consume even two-thirds o f the NRC RDA's. These f i g u r e s suggest that d i e t s of vegetarians were no poorer i n t o t a l i r o n content than were those o f omnivores and f i s h eaters and i n the case of v e g e t a r i a n women i r o n intakes were somewhat b e t t e r than f o r the other two groups. A s c o r b i c a c i d intake which i s known t o enhance u t i l i z a t i o n o f non-heme i r o n was a l s o found to be higher among v e g e t a r i a n women than f o r the other two groups s t u d i e d . Iron and a s c o r b i c a c i d intake of a d u l t v e g e t a r i a n men and women i n comparison t o the NRC RDA's were a l s o reported by Brown and Bergan (26). S i m i l a r l y , as i n the p r e v i o u s l y reported study by Tober and Cook, v e g e t a r i a n men had mean i r o n intakes of 148% of the NRC RDA's but the f i g u r e f o r v e g e t a r i a n women was only 62% of t h i s standard. Mean a s c o r b i c a c i d intakes were 164 and 165% of the standards f o r a d u l t men and women. Using a d i f f e r e n t approach, A b d u l l a e t a l . (27) analyzed n u t r i e n t contents of 1-day d i e t s of 6 s t r i c t Swedish vegetarians (vegans) using a d u p l i c a t e p o r t i o n sampling technique. The vegan d i e t s provided 17 ± 6 mg of i r o n f o r men and 16 ± 7 mg o f i r o n f o r women. Iron d e n s i t y of the vegan d i e t s was found t o be s i g n i f i c a n t l y higher than that f o r a normal mixed d i e t (9.0 ± 2.4 v s . 65 ± 1.9). D i e t a r y f i b e r which has been i m p l i c a t e d as an i r o n absorption i n h i b i t o r was a l s o found to be consumed i n l a r g e amounts i n the vegan d i e t s w i t h men consuming 62 ± 9 g/day and women consuming 43 ± 9 g/day. D i e t a r y f i b e r d e n s i t y was a l s o found t o be s i g n i f i c a n t l y higher i n the vegan d i e t s than i n normal mixed d i e t s (29.4 ± 4 v s . 6.3 ± 2 ) . In a study from t h i s l a b o r a t o r y , i r o n intakes and i r o n n u t r i t i o n a l s t a t u s of Seventh Day A d v e n t i s t students attending Union C o l l e g e i n L i n c o l n , Nebraska were s t u d i e d . As a beginning study, 28 Seventh-Day A d v e n t i s t students were asked t o keep 3day d i e t a r y d i a r i e s . Of the 28 s u b j e c t s , 15 claimed t o be veget a r i a n s and 13 claimed t o be omnivores. Most meals and food eaten by the subjects were obtained from the Union C o l l e g e c a f e t e r i a which i s operated as a lacto-ovo-vegetarian food s e r v i c e . A l l foods served were sampled f o r i r o n analyses. F a s t i n g blood serum samples were drawn on the morning f o l l o w i n g the t a k i n g o f the l a s t food recorded. The 13 subjects who claimed t o be omnivores a c t u a l l y consumed very l i t t l e meat during the course o f the study; hence, r e a l l y were much l i k e the omnivores consuming a vegetarian d i e t . As shown i n Table I , i r o n intakes of both groups was approximately the same with mean values being only about one-half the NRC RDA allowances f o r t h i s age/sex group. However, a s c o r b i c a c i d intake l e v e l s were high which might have helped i n the u t i l i z a t i o n of the i r o n provided. Hemoglobin and hematocrit l e v e l s which are sometimes used as indexes of adequate i r o n 1


187



188


Table I Iron N u t r i t i o n a l Status of Omnivore and Vegetarian Students E a t i n g a Lacto-Ovo-Vegetarian Food S e r v i c e D i e t ( S e l f - S e l e c t e d )

Number of s u b j e c t s Serum i r o n

(ug/dl)

Omnivores

Vegetarians

13

15

121

124

36.48

24.84

Hemoglobin (g/dl)

14.05

13.95

Hematocrit

42.04

41.67

Iron i n t a k e (mg/day), c a l c u l a t e d

10.36

10.60

A s c o r b i c a c i d i n t a k e (mg/day)

95.6

Serum f e r r i t i n

(mg/ml)

(%)

125

P r e l i m i n a r y data, L. McEndree



12.

KIES AND MCENDREE

189

Vegetarianism

n u t r i t i o n were i n the normal range f o r both groups o f s u b j e c t s as were the serum i r o n l e v e l s . However, the serum f e r r i t i n l e v e l s of the v e g e t a r i a n subjects were s i g n i f i c a n t l y lower than those f o r omnivore groups suggesting that the v e g e t a r i a n s u b j e c t s had lower i r o n s t o r e s than d i d the omnivore students. Iron intakes and n u t r i t i o n a l s t a t u s of 56 o l d e r Canadian Seventh-Day A d v e n t i s t women (mean age 52.9 ± 15.3 years) who had been f o l l o w i n g v e g e t a r i a n d i e t s f o r 19 ± 17 years were reported by Anderson e t a l . (25). Iron i n t a k e s were c a l c u l a t e d from 3-day d i e t a r y d i a r i e s . Mean i r o n intakes o f the 25 veget a r i a n women who were not t a k i n g i r o n supplements was 12.5 mg/ day from food with a range o f 7.3 t o 19.3 mg/day and mean d i e t a r y f i b e r intake was 30.9 mg/day with a range of 10.6 t o 68.3 mg. Percentage c o n t r i b u t i o n s o f the food groups t o t o t a l i r o n intakes were as f o l l o w s : 32% from bread and c e r e a l s , 25% from vegetables, 18% from d r i e d legumes and nuts ( i n c l u d i n g soya p r o d u c t s ) , 18% from f r u i t , 6% from m i l k and eggs, and 2% from f a t s , o i l s , beverages and a l c o h o l . Mean hemoglobin, serum i r o n , t o t a l i r o n b i n d i n g c a p a c i t y and serum t r a n s f e r r i n l e v e l s of the v e g e t a r i a n women t a k i n g i r o n supplements were 12.9 g / d l , 135 ug/dl, 346 ug/dl and 39%, r e s p e c t i v e l y , and those f o r women not t a k i n g i r o n supplements were 13.2 g / d l , 107 ug/dl, 312 ug/dl and 36%, r e s p e c t i v e l y . In s p i t e o f low i r o n intakes and high f i b e r i n t a k e s , these veget a r i a n women e x h i b i t e d normal biochemical indexes o f i r o n s t a t u s whether o r not they were c o n c u r r e n t l y consuming i r o n supplements. From the r e s u l t s o f these s t u d i e s i t would appear that d i e t s of both v e g e t a r i a n and omnivore women tend t o c o n t a i n l e s s than recommended t o t a l amounts o f i r o n . Furthermore, the i r o n i n v e g e t a r i a n d i e t s tends t o come from foods of suspected low i r o n b i o a v a i l a b i l i t y . However, on the b a s i s of biochemical i n d i c e s of i r o n s t a t u s , most seemed t o be i n adequate n u t r i t i o n a l s t a t u s . Recently, Bergan and Brown (29), reported r e s u l t s of a study i n v o l v i n g new v e g e t a r i a n s . R e s u l t s i n d i c a t e d that 50% had non-acceptable hematocrit l e v e l s ; 23% had non-acceptable hemoglobin l e v e l s , 18% had non-acceptable serum i r o n l e v e l s , 14% had non-acceptable t r a n s f e r r i n s a t u r a t i o n l e v e l s , and 7% had non-acceptable serum a s c o r b i c a c i d l e v e l s . Comparative U t i l i z a t i o n o f Iron by Vegetarians

and Omnivores

Considerable research e x i s t s from l a b o r a t o r y s t u d i e s i n d i c a t i n g that i r o n contained i n v e g e t a r i a n d i e t s should not be well u t i l i z e d . Furthermore, r e s u l t s from survey s t u d i e s suggest that i r o n intakes of v e g e t a r i a n women tend to be low i n comparison t o recommended standards of i n t a k e . However, biochemical indexes o r i r o n s t a t u s among these women do not suggest a h i g h incidence o f i r o n d e f i c i e n c i e s . Therefore, a research p r o j e c t was undertaken a t the U n i v e r s i t y of Nebraska t o study the compara t i v e u t i l i z a t i o n of i r o n by v e g e t a r i a n and omnivore s u b j e c t s i n several laboratory c o n t r o l l e d diet studies.



190

NUTRITIONAL BIOAVAILABILITY

OF IRON

In the f i r s t comparison 12 lacto-ovo-vegetarians who p a r t i c i p a t e d i n s e v e r a l d i f f e r e n t n u t r i t i o n a l s t u d i e s were p a i r matched by age, sex, s i z e , weight and e t h n i c background to 12 omnivore s u b j e c t s who p a r t i c i p a t e d i n the same s t u d i e s . A l l subjects consumed a l a b o r a t o r y c o n t r o l l e d v e g e t a r i a n d i e t based on peanut b u t t e r , milk, bread, f r u i t s and vegetables f o r 21 to 28 days. While s e v e r a l d i f f e r e n t experimental treatments i n the form of d i e t a r y a d d i t i v e s were employed i n these s t u d i e s , only data from the c o n t r o l p e r i o d when no f u r t h e r experimental v a r i a b l e s were employed were used i n t h i s comparison. As shown on Table I I , serum i r o n l e v e l s , hemoglobin l e v e l s , and hematocrit l e v e l s were not s i g n i f i c a n t l y d i f f e r e n t between the two groups. However, the v e g e t a r i a n subjects d i d show a s i g n i f i c a n t l y higher i r o n b i n d i n g c a p a c i t y i n comparison to omnivore s u b j e c t s (342 ug/dl v s . 312 u g / d l ) . T h i s suggests that the vegetarians had an increased need f o r i r o n and p h y s i o l o g i c a l l y responded by i n c r e a s i n g t h e i r c a p a c i t y f o r absorption. Fecal i r o n e x c r e t i o n of the v e g e t a r i a n s u b j e c t s was somewhat l e s s a t 20.6 mg/day than was the f e c a l i r o n e x c r e t i o n f o r the omnivore subjects (21.8 mg/day) w h i l e both groups r e c e i v e d the l a c t o v e g e t a r i a n d i e t . While these d i f f e r e n c e s were only s i g n i f i c a n t at the 10% l e v e l of p r o b a b i l i t y , they do suggest trends of b i o l o g i c a l i n t e r e s t . Percent i r o n recovery from feces was c a l c u l a t e d as the f e c a l i r o n d i v i d e d by the d i e t a r y i r o n x 100. T h i s i m p l i e s that a l l f e c a l i r o n i s unabsorbed d i e t a r y i r o n which i s , of course, a f a l s e assumption. T h i s c a l c u l a t i o n i s u s e f u l , however, i n minimizing some of the small v a r i a t i o n s i n i n d i v i d u a l intakes of i r o n among s u b j e c t s . Vegetarians w h i l e r e c e i v i n g the l a c t o - v e g e t a r i a n d i e t had a mean f e c a l i r o n recovery of 86.37% w h i l e the omnivore subjects had a mean f e c a l i r o n recovery of 93.2%. T h i s i m p l i e s (but does not prove) that the v e g e t a r i a n subjects were b e t t e r u t i l i z i n g the i r o n provided by the v e g e t a r i a n d i e t than were the omnivore s u b j e c t s . Data from v e g e t a r i a n and omnivore subjects were s p e c i f i c a l l y examined r e l a t i v e to the experimental plans of s e v e r a l s t u d i e s which have d i r e c t bearing on i r o n u t i l i z a t i o n . S i x subjects who were p a r t i c i p a n t s i n a study on e f f e c t s of s e v e r a l p u r i f i e d f i b e r s on n u t r i e n t u t i l i z a t i o n and who were vegetarians were age, sex, h e i g h t , weight and ethnic-group matched w i t h s i x subjects from t h i s s e r i e s of s t u d i e s who were omnivores. The l a b o r a t o r y c o n t r o l l e d d i e t f e d t o a l l subjects f o r 21-28 days was of the l a c t o - v e g e t a r i a n type p r e v i o u s l y d e s c r i b e d . The b a s a l d i e t p r o vided 25.3 mg o f i r o n and 14.7 g of f i b e r . C e l l u l o s e , h e m i c e l l u l o s e or p e c t i n were added to the b a s a l d i e t to provide 20 g of f i b e r / d a y i n separate, randomly arranged periods of 6 to 7 days each. As shown i n Table I I I , blood serum i r o n l e v e l s v a r i e d n e i t h e r between groups o r as a r e s u l t of f i b e r supplementation of d i e t s i n any c o n s i s t e n t f a s h i o n . This*was a l s o true of hematocrit values


12.

KIES AND MCENDREE

191

Vegetarianism


Table I I Iron N u t r i t i o n a l Status of Omnivore and Vegetarian Subjects Consuming Laboratory C o n t r o l l e d , Vegetarian D i e t s

Omnivores

Vegetarians

Number of s u b j e c t s

12

12

Serum i r o n

94

95

312

342

(ug/dl)

Iron b i n d i n g c a p a c i t y (ug/dl) Hemoglobin (g/dl)

13-7

13.6

Hematocrit (%)

42,3

42.1

Dietary iron

23.4

23.4

21.8

20.2

93.2

86.3

Fecal iron

(mg/day)

(mg/day)

Iron recovery from feces (%)


192


Table I I I


Iron U t i l i z a t i o n o f Omnivore and Vegetarian Human Subjects Fed Laboratory C o n t r o l l e d Vegetarian D i e t s With and Without F i b e r Supplements Mean v a l u e while r e c e i v i n g f o l l o w i n g d i e t Parameter

B a s a l alone + c e l l u l o s e

Blood serum i r o n (mg/dl) Omnivores Vegetarians

96 94

Blood hematocrit (%) Omnivores Vegetarians

41.7 42.2

a

94 94

a

95 96

a

Blood hemoglobin (g/dl) Omnivores 13.8 Vegetarians 13.7

+hemicellulose +pectin

a

a

a

a

Iron b i n d i n g c a p a c i t y (ug/dl) Omnivores 318!* Vegetarians 347 F e c a l i r o n e x c r e t i o n (mg/day) Omnivores 22.4 Vegetarians 20.3 a

a

42.3 42.4

a

13.8 13.8

a

a

a

b

22.9 20.4

a

a

Percentage food i r o n recovered i n f e c e s Omnivores 88.6 90.4 Vegetarians 80.3 81.0 a

a

b

a

42.7 42. l

a

13.7 13.5

a

320 352

315? 348

96 94

a

a

a

42.l 42.7

b

24.0 21.0

b

95.0 82.4

a

a

a

13.9 13.5 310 340

a

a

a

a

a

a

a

b

22.6 20.3

a

a

(%) b

89. l 80. l

Note: Values with the same l e t t e r s u p e r s c r i p t not s i g n i f i c a n t l y d i f f e r e n t at P

Vegetarianism and the Bioavailability of Iron - ACS Symposium Series

Recommend Documents