10 Bioavailability of Iron from Bran in Pigs Nutritional Bioavailability of Iron Downloaded from pubs.acs.org by UNIV OF TEXAS AT EL PASO on 11/04/18. For personal use only.
WENCHE FRØLICH Norwegian Cereal Institute, P.O. Box 8116, Dep., Oslo 1, Norway
In most countries, cereals are the largest single source of dietary iron. The iron content of white flour is considerably lower than that of whole grain flour and flours of higher extraction rate. In Norway we have no fortification of the white flour, and the contribution of iron from cereals to the diet accounts for only 30%. Our neighbor country Sweden does enrich its white flour, with the result that over 60% of the iron in the diet comes from cereals. The frequency of iron anemia is, nevertheless, the same in the two countries. Bran has been claimed to reduce iron absorption. The aim of this study was to evaluate the bioavailability of iron in pigs in a diet with a high content of bran (6-10%). The results did not show any sign of inhibitory effect on iron absorption from bran, either in short-term experiments or in long-term experiments. It should be stressed that this applies to pigs and should be tested on humans before any further conclusions are drawn. Norway i s a mountainous country and agriculture is difficult* The result of this i s that Norway i s importing about 80% of the grain for human consumption. This gives us the benefit of selecting cereals with the quality we consider best, both from a nutritional and technological point of view. In the Whitebook from the Government to the Parliament called Report No. 32 on Norwegian Nutrition and Food Policy from 1975, (1) the authorities are trying to stimulate the consumer and producer towards a diet which should be suitable. It is necessary to have a diet which provides sufficient energy and which ensures adequate supplies of a l l necessary nutrients and other desirable ingredients. The nutrition and food policy should coordinate several important objectives and considerations. 0097-6156/82/0203-0163$06.00/0 © 1982 American Chemical Society
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O b j e c t i v e s of the n u t r i t i o n and food p o l i c y may be summarized as follows: 1. Healthy d i e t a r y h a b i t s should be encouraged, 2. A n u t r i t i o n and food p o l i c y should be formulated i n accordance with the recommendations of the World Food Conference* 3. For reasons connected w i t h the question of supply, the p o l i c y should aim at i n c r e a s e d p r o d u c t i o n and consumption of food and a t s u f f i c i e n c y i n the food supply. 4. For r e g i o n a l p o l i c y reasons, the h i g h e s t p r i o r i t y should be placed on u t i l i z i n g the food production resources i n the econo m i c a l l y weaker areas. Considerable s h i f t s have taken p l a c e i n the number and types of energy-providing foods. The p r o p o r t i o n of f a t s i n the energy supply has i n c r e a s e d , w h i l e the p r o p o r t i o n of carbohydrates has decreased w i t h a reduced consumption of s t a r c h e s , although the consumption of sugar i n c r e a s e d . The N a t i o n a l N u t r i t i o n C o u n c i l s t r e s s e s that a r e d u c t i o n of the energy supply from f a t and an i n c r e a s e i n the energy supply from carbohydrates i s d e s i r a b l e . There should be a greater use of s t a r c h e s . An i n c r e a s e i n the consumption of c e r e a l products would be a b e n e f i t i n s e v e r a l n u t r i t i o n a l r e s p e c t s . Over a p e r i o d of the percent of food consumption represented by g r a i n has g r a d u a l l y f a l l e n to about 70 kg per year per person i n 1970. In the past few years,however, t h i s tendency seems to have been r e v e r s e d and i t i s today 80 kg per year per person. It i s our g o a l to i n c r e a s e the consumption of g r a i n to 90 kg per person per year during the p e r i o d before 1990. One way of doing t h i s i s to have a r e l a t i v e l y cheap and s t a b l e p r i c e on c e r e a l s . Today we have a p r i c e system f o r g r a i n where the p r i c e i s i n d e pendent of f l u c t u a t i o n s on the world market p r i c e and a l s o i n d e pendent of the producer p r i c e f o r Norwegian food g r a i n . The e x t r a c t i o n r a t e i n Norway of 78-80% must be considered r e l a t i v e l y h i g h compared w i t h that of other c o u n t r i e s , but even such a f l o u r has s i g n i f i c a n t l y l e s s i r o n than whole wheat f l o u r (Table I ) . Table I .
Content of M i n e r a l s , Vitamin B and D i e t a r y F i b e r i n 100 g of D i f f e r e n t Wheat Products Minerals Calcium Iron (mg) (mg)
Thiamin (mg)
Vitamin B Riboflavin (mg)
Dietary F i b e r (g)
Whole g r a i n wheat f l o u r Wheat f l o u r
40
3.5
0.43
0.15
12.6
20
1.5
0.24
0.06
3.2
120
12.0
0.70
0.24
52.8
78%
extraction rate Bran of wheat flour
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An Increase i n our e x t r a c t i o n r a t e has been considered. This would r e s u l t i n greater s u p p l i e s of minerals, vitamins and dietary f i b e r . In Norway only 17% of the t o t a l f l o u r consumed i s whole grain f l o u r . A considerable i n c r e a s e would be d e s i r a b l e from a n u t r i t i o n i s t ' s p o i n t of view. The f r a c t i o n of the f l o u r consumed as white bread has been remarkably s t a b l e , although l a r g e campaigns have been performed encouraging the use of whole g r a i n flour. The Iron S i t u a t i o n i n Norway Hemoglobin s t u d i e s i n d i c a t e that i r o n - d e f i c i e n c y anemia i s q u i t e common i n our population, e s p e c i a l l y i n women between ages 15 and 50. Cereals and c e r e a l products are not only the l a r g e s t s i n g l e source of energy, but a l s o a main source of d i e t a r y i r o n . In many c o u n t r i e s the i r o n content of bread made from white f l o u r i s t h e r e f o r e increased by f o r t i f y i n g the white f l o u r with i r o n . But there i s a l s o another way to i n c r e a s e the i r o n content i n the d i e t and that i s to i n c r e a s e the consumption of whole g r a i n f l o u r . In Norway we have no f o r t i f i c a t i o n of f l o u r , a c o n c l u s i o n drawn long a f t e r d i s c u s s i o n s and some years with i r o n f o r t i f i c a t i o n i n some areas. Because of long storage time f o r f l o u r i n Norway, d i s c o l o r i n g due to i r o n f o r t i f i c a t i o n has been a r e s u l t . The added compounds have a l s o been shown to have a negative e f f e c t on the storage s t a b i l i t y . For some years the enrichment i n g r e d i e n t s were then added to the dough at the time of breadmaking. T h i s turned out to be i n convenient f o r the bakers, and a f t e r a short p e r i o d , t h i s put an end to the i r o n f o r t i f i c a t i o n i n our country. We i n the Norwegian N u t r i t i o n C o u n c i l t h i n k i t i s a b e t t e r p o l i c y to give the consumer information and education about which foods are the best i r o n sources and to encourage them to eat more of these unrefined products. Our neighbor country, Sweden, has a d i f f e r e n t p o l i c y . They do e n r i c h t h e i r white f l o u r , with the r e s u l t that 2/3 of the i r o n i n the d i e t comes from c e r e a l s , 42% of the t o t a l i r o n i s from fortification. I t i s worthwhile to mention that the frequency of i r o n anemia i s the same i n our two c o u n t r i e s . Common n u t r i t i o n a l recommendations are a goal i n Scandinavia. Because of the d i f f e r e n t f o r t i f i c a t i o n p o l i c i e s concerning i r o n , an agreement on i r o n recommendations has been d i f f i c u l t . With a Norwegian food p a t t e r n and with no f o r t i f i c a t i o n , i t i s hard to get more than 15 mg d i e t a r y i r o n per day, which has been the Norwegian recommendation f o r a d u l t women. The corresponding value i n Sweden i s 18 mg per day. No agreement has yet been reached, but p r e l i m i n a r y steps have been taken. Table I I shows current recommendations•
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Recommended D a i l y
C h i l d r e n up to 6 months C h i l d r e n from 6 months Adults
Allowances
Sweden 10 mg 15 mg 18 mg
Norway 5 mg 10 mg 12-18 mg
One way to i n c r e a s e the b i o a v a i l a b i l i t y of i r o n i n the d i e t i s to i n c r e a s e the content of f a c t o r s s t i m u l a t i n g i t s a b s o r p t i o n . A s c o r b i c a c i d i s known t o i n c r e a s e the a b s o r p t i o n of i r o n . The Norwegian recommendation of a s c o r b i c a c i d i n the d i e t was u n t i l r e c e n t l y 30 mg per day. But we have accepted the Swedish recommendation of 60 mg per day p a r t l y because the b i o a v a i l a b i l i t y of the i r o n could be improved. Iron and Whole G r a i n C e r e a l s An i n c r e a s e i n consumption of whole g r a i n f l o u r products i s the n u t r i t i o n a l aim i n Norway. The h i g h content of d i e t a r y f i b e r or f a c t o r s a s s o c i a t e d w i t h i t , however, present i n bran and whole g r a i n f l o u r , may i n t e r f e r e w i t h the b i o a v a i l a b i l i t y of i r o n as i n d i c a t e d by s e v e r a l authors (2,3»4) • Phosphate and e s p e c i a l l y p h y t i c a c i d present i n u n r e f i n e d c e r e a l products have f r e q u e n t l y been s a i d to be potent i n h i b i t o r s of i r o n a b s o r p t i o n (5,6). On the other hand, M o r r i s et a l . (7) r e c e n t l y pointed out that n a t u r a l l y o c c u r i n g i r o n i n wheat i s predominantly present i n the form of monoferric phytate, which ( u n l i k e phytate complexed with two or more i r o n atoms) i s s o l u b l e a t pH 7.0 and above and may t h e r e f o r e be a r e l a t i v e l y a v a i l a b l e form of d i e t a r y i r o n . C o n f l i c t i n g r e p o r t s i n the l i t e r a t u r e on the e f f e c t of phytate on i r o n a b s o r p t i o n might be due to the use of d i f f e r e n t f e r r i c phytate complexes i n the v a r i o u s s t u d i e s . Other f a c t o r s i n the whole g r a i n bread have been pointed out as i n h i b i t o r s of i r o n . Reinhold e t a l . (8) concluded that f i b e r i n whole g r a i n products might be r e s p o n s i b l e f o r the decreased mineral a b s o r p t i o n , because i t remains undigested i n the small i n t e s t i n e . A l l these c o n f l i c t i n g r e p o r t s have c a l l e d i n t o question the v a l u e of whole g r a i n bread i n the d i e t . B i o a v a i l a b i l i t y of I r o n from Bran i n P i g s On the b a s i s of t h i s i t was of i n t e r e s t to study what i n f l u ence a h i g h content of f i b e r would have on the b i o a v a i l a b i l i t y of i r o n i n the d i e t . For many consumers bran has become almost synonymous w i t h f i b e r , which i s not the case. But bran i s the most concentrated form of f i b e r and cheaply a v a i l a b l e to the general p u b l i c . In the work I w i l l present here, wheat bran w i t h a f i b e r content of 60% was used as a source of f i b e r . Previous s t u d i e s of t h i s k i n d have i n most cases used r a t s as experimental animals. The h i g h a v a i l a b i l i t y of i r o n i n the
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presence o f phytate i n r a t s c o u l d be a t t r i b u t e d t o the presence of an i n t e s t i n a l phytase that might l i b e r a t e food i r o n as the phytate i s degraded. I t does not seem that the human i n t e s t i n a l t r a c t possesses t h i s enzyme. I f p h y t i c a c i d does i n f l u e n c e the i r o n a b s o r p t i o n , a p a r a l l e l i s d i f f i c u l t t o draw between r a t s and humans. As i n humans the enzyme has not been demonstrated i n p i g s and, f o r t h i s reason, p i g s were chosen f o r experimental animals • The p r o j e c t was done i n cooperation w i t h Dr. Lyso and P r o f e s s o r Homb a t the A g r i c u l t u r a l High School i n Norway. The experiments were s t a r t e d d i r e c t l y a f t e r the p i g s were born. There were about 10 p i g s i n each l i t t e r , both male and female. The weight o f the p i g s r i g h t a f t e r b i r t h was around h a l f a k i l o . Right a f t e r b i r t h , a l l the p i g s were given an almost i r o n f r e e diet. I n a d d i t i o n t o mother's m i l k they got fodder c o n t a i n i n g skimmed dry m i l k , white f l o u r , soya f l o u r , sugar, s a l t , v i t a m i n s and m i n e r a l s (except f o r i r o n ) . The t o t a l content o f i r o n i n t h i s d i e t was 17 mg per k i l o . The d i e t was the same f o r a l l p i g s , and they were f r e e t o eat as much as they wanted u n t i l they were taken from t h e i r mother, a t around 7 weeks o l d . The surroundings i n which the p i g s l i v e d were a l s o completely i r o n f r e e , and because they l i v e d indoors they d i d not get h o l d o f any e a r t h , i n which i r o n c o u l d c o n t r i b u t e t o the d i e t . The need f o r i r o n i n t h i s p e r i o d i s 50 mg/kg d i e t . A f t e r 5 t o 7 weeks the p i g s became very anemic. The hemoglobin had decreased t o around 5 g/ 100 ml. The normal hemoglobin f o r p i g s i s 13 g/100 ml. At t h i s time the p i g s were d i v i d e d i n t o two groups: 1. The r e f e r e n c e group 2. The bran group The bran group got 6% o f bran i n t h e i r d i e t . Except f o r the bran the d i e t was the same f o r the two groups. The content o f i r o n i n the d i e t s was not p l e n t i f u l . The t o t a l i r o n c o n c e n t r a t i o n was the same i n the two groups. T h i s means that the bran group, which had e x t r a i r o n from bran, had a lower a d d i t i o n o f i r o n i n the r e s t of the d i e t . The a d d i t i o n o f i r o n i n the r e f e r e n c e group was o n l y f e r r o u s sulphate, w h i l e i n the bran group, 60% o f the i r o n came from bran and 40% from f e r r o u s sulphate. In t h i s p a r t o f the experiment the a d d i t i o n o f i r o n was: 1. 2.
Reference group Bran group
103 mg Fe per k i l o 111 mg Fe per k i l o
diet diet
At the time o f grouping the p i g s were extremely anemic, n e a r l y yellow i n c o l o r . The growth i n t h i s f i r s t p e r i o d was somewhat reduced. With the a d d i t i o n of i r o n the p i c t u r e changed very r a p i d l y . The a p p e t i t e of the p i g s was very good and the growth was f o r a l l
NUTRITIONAL BIOAVAILABILITY OF IRON
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p i g s greater than normal. A l s o the blood p i c t u r e a l t e r e d r a p i d l y , but was d i f f e r e n t i n the two groups* Blood samples were taken each week f o r 6 weeks* The hemog l o b i n and serum i r o n were determined i n each sample* For both hemoglobin and serum i r o n the v a l u e s i n c r e a s e d most r a p i d l y i n the bran group* A f t e r 2-3 weeks they had reached a hemoglobin l e v e l of 10, w h i l e the r e f e r e n c e group used a c o n s i d e r a b l y longer time* The same was t r u e f o r serum i r o n * T h i s was s i g n i f i c a n t f o r a l l the p i g s , a l t o g e t h e r 10 p i g s i n each group, w i t h a standard d e v i a t i o n of 5-6%. The c o n c l u s i o n of t h i s must be t h a t there i s no greater r i s k f o r i r o n anemia i n p i g s w i t h a d i e t c o n t a i n i n g a c o n s i d e r able amount of bran and f i b e r than without bran* G i v i n g the same amount of bran i n a d d i t i o n to the d i e t during a long p e r i o d , p i g s never gave any s i g n of anemia. On the c o n t r a r y , there was a tendency towards b e t t e r i r o n b i o a v a i l a b i l i t y f o r the bran p i g s . In an a d d i t i o n a l experiment the p i g s were given Fe59 to study the b i o a v a i l a b i l i t y of i r o n i n the bran d i e t a f t e r c o n t i n uous bran a d d i t i o n f o r 8 months. There was no d i f f e r e n c e i n i r o n i n the bran group and the r e f e r e n c e group. Conclusions Concerning P i g Experiment In these experiments w i t h p i g s there were no i n d i c a t i o n s that bran had an i n h i b i t o r y e f f e c t on i r o n a b s o r p t i o n . I t seems that i r o n from bran i s as b i o a v a i l a b l e as f e r r o u s sulphate even from a d i e t c o n t a i n i n g a r e l a t i v e l y h i g h p o r t i o n of bran, i n an anemic s i t u a t i o n . T h i s c o u l d be expressed i n the f o l l o w i n g way: 1. 2.
3.
Iron i n bran and whole g r a i n c e r e a l products i s as good a source f o r i r o n as i n o r g a n i c i r o n . Bran does not seem to have any i n h i b i t o r y e f f e c t on the a b s o r p t i o n of i r o n , e i t h e r on i n o r g a n i c i r o n or on n a t u r a l l y o c c u r i n g i r o n from c e r e a l s . I f a d d i t i o n of bran r e s u l t s i n a higher a b s o r p t i o n of i r o n , as the tendency i s i n our experiments, t h i s c o u l d be i n t e r p r e t e d i n the f o l l o w i n g way: a) Iron from c e r e a l products i s a b e t t e r source of i r o n than i n o r g a n i c i r o n . b) F a c t o r s i n bran have a p o s i t i v e e f f e c t on the t o t a l iron absorption.
I t should be s t r e s s e d t h a t t h i s a p p l i e s to p i g s and should be t e s t e d on humans before any f u r t h e r c o n c l u s i o n s are drawn. Experiments on p i g s are now being performed where i r o n from c e r e a l s i s the only source of i r o n . So f a r i t seems that the i r o n a b s o r p t i o n i s as good f o r the b r a n - c e r e a l p i g s as f o r the p i g s i n the r e f e r e n c e group which get a l l t h e i r i r o n from f e r r o u s sulphate•
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In V i t r o Experiments on D i e t a r y F i b e r The d i e t a r y f i b e r content of v a r i o u s Norwegian wheat f l o u r s (9) w i t h d i f f e r e n t e x t r a c t i o n r a t e s were analyzed. To analyze the d i e t a r y f i b e r content we used a g r a v i m e t r i c method, based on d i g e s t i o n o f the samples w i t h pepsin and p a n c r e a t i n . The method i s a m o d i f i c a t i o n of the procedure described by Hellendorn et a l . and modified by Asp e t a l (10)• The pepsin d i g e s t i o n was c a r r i e d out a t pH 1.5 f o r 1 h r , and the p a n c r e a t i n d i g e s t i o n at pH 6.8 f o r 1 h r . I n s o l u b l e components were recovered by f i l t r a t i o n a f t e r enzyme d i g e s t i o n , and s o l u b l e components a f t e r p r e c i p i t a t i o n with a l c o h o l and another f i l t r a t i o n . The f i b e r values thus obtained were c o r r e c t e d f o r remaining t r a c e s of s t a r c h and p r o t e i n . The ash content o f the w a t e r - s o l uble and w a t e r - i n s o l u b l e f i b e r f r a c t i o n s was determined g r a v i m e t r i c a l l y a f t e r i g n i t i o n a t 550°C. (Dietary f i b e r values do not i n c l u d e t h i s ash). The w a t e r - i n s o l u b l e f r a c t i o n c o n s t i t u t e s 70-94% of the t o t a l d i e t a r y f i b e r , but does not c o n t a i n measurable amounts o f ash. The s o l u b l e f i b e r components, on the other hand, were a s s o c i a t e d with c o n s i d e r a b l e amounts o f ash, and there seems t o be a l i n e a r c o r r e l a t i o n between s o l u b l e f i b e r and ash (11) as shown i n Figure 1. The nature o f the b i n d i n g i s under i n v e s t i g a t i o n . Conclusion In c o n c l u s i o n , the i n s o l u b l e f r a c t i o n , which i s by f a r the main p a r t o f c e r e a l d i e t a r y f i b e r , does not bind measurable amounts of ash a f t e r d i g e s t i o n with p r o t e o l y t i c and a m y l o l y t i c enzymes under c o n d i t i o n s s i m i l a r t o those i n the human g a s t r o i n t e s t i n a l t r a c t . A l l the b i n d i n g c a p a c i t y seems t o be due t o the small s o l u b l e f r a c t i o n i n which the polysaccharides but a l s o most o f the p h y t i c a c i d i s recovered. Thus, i f these i n v i t r o experiments r e f l e c t what i s going on i n the i n t e s t i n e s , the f i b e r s i n bran do not seem t o bind ash ( i n c l u d i n g i r o n ) , and are t h e r e f o r e i n good agreement w i t h the good b i o a v a i l a b i l i t y of i r o n from bran i n the p i g s .
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Figure 1. Relation between the soluble dietary fiber fraction and associated ash in wheat products. (Reproduced, with permission, from Ref. 11. Copyright 1980, American Society for Clinical Nutrition.)
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Literature Cited 1. Royal Norwegian Ministry of Agriculture: On Norwegian Nutrition and Food Policy. Whitebook No. 32 to the Parliament, Nov., 1975. 2. Jenkins, D.J.A.; H i l l , M.S.; Cummings, J.H. Am. J. Clin. Nutr. 1975, 28, 104. 3. Bjorn-Rasmussen, E. Nutr. Metabol. 1974, 16, 101. 4. Widdowsen, E.M., McCance, R.A. Lancet 1942, 1, 588. 5. Sharpe, L.M.; Peacock, W.G.; Cooke, R.; Harris, R.S. J. Nutr. 1950, 41, 433. 6. Hussain, R.; Patwardhan, V.H. Ind. J. Med. Res. 1959, 47, 676. 7. Morris, E.R.; Ellis, R. J. Nutr. 1976, 106, 753. 8. Reinhold, J.G.; Ismail-Beigi, F.; Faradji, B. Nutr. Rep. Int. 1975, 12, 75. 9. Frolich, W.; Asp, N.G. Cereal Chemistry (in press). 10. Asp, N.G.; Johansson, C.G.; Hallmer, H.; Silgestrom, M. J. Food. Agr. Chem. (submitted). 11. Frolich, W.; Asp, N.G., Am. J. Clin. Nutr. 1980, 33, 2397. RECEIVED
August 13,
1982.
