Zinc Absorption from Composite Meals - ACS Symposium Series (ACS

15 Zinc Absorption from Composite Meals WENCHE FRØLICH Norwegian Cereal Institute, National Institute of Technology, Oslo1,Norway

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BRITTMARIE SANDSTRØM Sahlgrenska Sjukhuset, Institutt for klinisk näringslära, 41345 Gøteborg, Sweden Zinc absorption was measured from meals based on wheat bread. A lower absolute amount of zinc was absorbed from a low zinc white bread (72% extraction rate) than from a whole-meal bread with a higher zinc content (100% extraction rate). When the two types of bread where enriched with zinc chloride, more zinc was absorbed from the white bread. By increasing the zinc content of the whole meal bread i n form of animal protein sources, such as milk and cheese, the absorption increased to the same level as that from zinc-enriched white bread. Addition of calcium i n the form of milk products improved the absorption of zinc from a meal with whole meal bread. Zinc i s well established as an essential nutrient and signs of zinc deficiency i n man has been reported (1). In Norway zinc deficiency seems to be unusual, although a suboptimal supply i n certain groups i n the population might occur. The daily dietary requirement of zinc depends not only on the physiological requirements of zinc, but also on the composition of the meals. In Norway there i s essentially no f o r t i f i c a t i o n of foodstuffs (exception iron i n goat cheese, vitamin A and vitamin D i n margarine, and iodine i n s a l t ) . We have i n Norway an o f f i c i a l n u t r i t i o n and food policy since 1975 02). In this Whitebook from the Government to the P a r l i a ment, the authorities are trying to stimulate the consumer and producer towards a diet which should be more suitable. The n u t r i t i o n and food policy should coordinate several important objectives and considerations. Members of the National Nutrition Council which are appointed from the Social and Health Department are working with guidelines of this policy. The best way to reach this n u t r i t i o n a l goal is to give the consumer information and education about which foods are the best 0097-6156/83/0210-0211$06.00/0 © 1983 American Chemical Society Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


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sources f o r the d i f f e r e n t n u t r i e n t s , and to encourage them to eat more of these products, which u s u a l l y means more unrefined products i n the case of m i n e r a l s . The success i n reaching the goals which are p r e d i c t e d i n the n u t r i t i o n p o l i c y , depend on the research i n progress. An i n creased knowledge of the r e l a t i o n between n u t r i t i o n and h e a l t h r e q u i r e s comprehension of the n u t r i e n t s , among others how an i n s u f f i c i e n t supply of d i f f e r e n t n u t r i e n t s could l e a d to or be a part of the development of diseases. Even i f the d i e t i n Norway must be considered n u t r i t i o n a l l y adequate, g e n e r a l l y covering the r e q u i r e d e s s e n t i a l n u t r i e n t s , there could i n c e r t a i n groups i n the p o p u l a t i o n e x i s t an i n s u f f i c i e n t supply of c e r t a i n m i n e r a l s . An increased knowledge about the d i f f e r e n t minerals i n our d i e t i s important, and a l o t of work i s done i n many areas, e.g. on i r o n , z i n c , selenium and chromium. Improving the d i e t i s i n i t s e l f not enough. How an optimal b i o a v a i l a b i l i t y of the minerals could be o b t a i n i s as important as knowledge about the content of these m i n e r a l s . This paper w i l l deal w i t h the mineral z i n c , and how a meal could be composed i n such a way that a maximal absorption could be the r e s u l t . The amount of z i n c that the d i e t must contain^depends on the a v a i l a b i l i t y of z i n c f o r a b s o r p t i o n . The WHO committee gives no data f o r d i e t s , and the suggested d a i l y d i e t a r y requirement range from 2.8 mg i n infancy to 54.5 mg f o r l a c t a t i n g women. The United States Food and N u t r i t i o n Board suggest a d a i l y intake of 15 mg a day f o r a d u l t s ( 3 ) . The average intake of z i n c i n Norway i s 14.2 mg per person per day, where 30% i s coming from c e r e a l s . This i s except f o r meat, one of the l a r g e s t s i n g l e sources of z i n c i n our d i e t . An increase i n consumption of whole g r a i n f l o u r products i s one of the n u t r i t i o n a l aims i n Norway. The high 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 ^ 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 minerals as suggested by s e v e r a l authors (4, 5^ 6^, 7_ 8 ) . E s p e c i a l l y p h y t i c a c i d has been claimed to be a potent i n h i b i t o r of z i n c absorption and z i n c d e f i c i e n c y on high intake of p h y t i c a c i d have been shown i n d i f f e r e n t animals (9, 10). Knowledge about how an optimal absorptîon""c ou Id be obtained from whole g r a i n products i s of great v a l u e , since t h i s i s an important source of z i n c i n our d i e t . I t i s important to n o t i c e that i t i s not only the b i o a v a i l a b i l i t y of z i n c from bread which i s important, i t i s the b i o a v a i l a b i l i t y of z i n c from the composite meal where bread i s one of the components which gives the most i n t e r e s t i n g and u s e f u l i n f o r m a t i o n . In Sweden and Norway the e a t i n g p a t t e r n are r a t h e r common, and we have more or l e s s the same aim f o r our n u t r i t i o n p o l i c y . More u n r e f i n e d c e r e a l products i s an important f a c t o r i n t h i s effort for better eating habits. 9

Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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The experiments which are t o be described i n t h i s paper, were c a r r i e d out by Dr. B r i t t m a r i e Sandstr0m from the Department of C l i n i c a l N u t r i t i o n at the U n i v e r s i t y of Gothenburg, Sweden, ( 1 1 ) . The

aim of the study The aim of the present study was 1.


2.

To study the e f f e c t of p h y t i c a c i d , calcium and p r o t e i n i n bread meals i n v a r i o u s combination, on the z i n c ab s o r p t i o n i n man. To study the e f f e c t on z i n c absorption a f t e r enrichment with z i n c c h l o r i d e of bread w i t h d i f f e r e n t e x t r a c t i o n rate.

As z i n c d e f i c i e n c y has been observed on high intakes of whole f l o u r bread, 50% of the t o t a l energy of the meal was covered by bread. M a t e r i a l s and methods Subjects Healthy medical o r d i e t e t i c students and l a b o r a t o r y p e r s o n a l , a l l w i t h normal serum z i n c l e v e l s , volunteered f o r the study. T h i r t h y - f i v e women and t h i r t y - o n e men between nineteen and sixtyone years o f age (average 22 years) p a r t i c i p a t e d i n the experiment. No apparent d i f f e r e n c e s i n z i n c intake were found and they were not consuming mineral supplements. Absοrρtion me asurment The meals were e x t r i n s i c a l l y l a b e l l e d by added 65 Zn. The r a t i o n a l e f o r t h i s method i s that a complete isotope exchange takes place between the added r a d i o a c t i v e z i n c isotope and the z i n c present i n the meal. Measurements of the uptake of r a d i o a c t i v e i r o n isotopes i n blood o r i n the whole body have been used f o r many years i n studies of i r o n a b s o r p t i o n . (12, 13, 14). The absorption i n the present study i s determined from measurement of the whole body r e t e n t i o n of the r a d i o i s o t o p e . However, t h i s can not be done u n t i l the non-absorbed f r a c t i o n of the isotope has l e f t the body. During t h i s période of time some of the i n i t i a l l y absorbed ^^Zn has been e x t r e c t e d . A c o r r e c t i o n of r e t e n t i o n data f o r t h i s endogenous z i n c e x c r e t i o n i s made, based on f i g u r e s f o r the r a t e of e x c t e t i o n a f t e r i n t r a v e n o u s l y i n j e c t e d ^^Zn. In healthy subjects the d i f f e r e n c e s i n the r a t e of z i n c t u r n over are r e l a t i v e l y small and a standard c o r r e c t i o n can be made. Otherwise repeated measurements of the r a t e of e x c r e t i o n can be used t o e x t r a p o l a t e r e t e n t i o n t o absorption values at the time f o r intake of the meal. The r e t e n t i o n measurements i s done a f t e r two weeks to a l l o w f o r long bowel t r a n s i t time. The endogenous e x t r e t i o n of 65 Zn during t h i s period i s only about 10%. The r a d i o n u c t i d e technique w i t h 65 Zn and whole body counting are described i n more d e t a i l i n an other paper (15).


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P r e p a r a t i o n and composition of the meals In the present study, bread i n the form of r o l l s was prepared from whole g r a i n f l o u r (100% e x t r a c t i o n r a t e ) w i t h a z i n c content of 22 mg/kg and from white wheat f l o u r of about 72% e x t r a c t i o n r a t e , where the z i n c content was 7 mg/kg. The water added to the dough, contained an amount of almost c a r r i e r f r e e isotope s o l u t i o n , corresponding to 0.25 y / i C i of ^5 Zn f o r each r o l l . The isotope s o l u t i o n was made by d i l u t i n g a stock s o l u t i o n of 65 Zn C l i n 0.1 M HC1 (0.1 to 0.5 C i / g Zn, Radiochemical c e n t r e , Amersham, England) w i t h p h y s i o l o g i c a l s a l i n e to a f i n a l r a d i o a c t i v i t y of 1 ^ / C C i / m l . Each t e s t meal contained two r o l l s and 200 ml l i q u i d . A l l meals except f o r 2 meals were prepared to have a t o t a l z i n c content of 3.5 mg. I n those meals which d i d not have a n a t u r a l content of 3.5 mg z i n c , z i n c c h l o r i d e , was added d u r i n g p r e p a r a t i o n of the bread. The energy contents i n the d i f f e r e n t meals were e q u a l i z e d to 380 k c a l by s e r v i n g v a r i o u s amounts of b u t t e r w i t h the bread and v a r i o u s l i q u i d s (3% m i l k , 0.5% m i l k or w a t e r ) . The c a l c i u m content of the meals was increased by adding m i l k or lowfat cheese. In the s t u d i e s on the e f f e c t of p r o t e i n , the animal p r o t e i n sources were m i l k , cheese, b o i l e d beef and b o i l e d egg. To f u r t h e r i n c r e a s e , the p r o t e i n content without at the same time i n c r e a s i n g the c a l c i u m or z i n c content, sodium c a s e i n a t e was used i n one meal.


2

Exper iment a1 de s i g n On the b a s i s on the isotope technique d e s c r i b e d (15), the f o l l o w i n g experimental design was a p p l i e d : 1. 2. 3. 4. 5.

The meals were prepared i n advance, e x t r i n s i c a l l y l a b e l l e d and measured i n the whole body counter. Each subject f a s t e d f o r 12 hours. The t e s t meal was eaten, and no other tood was allowed f o r the f o l l o w i n g three hours. R e t e n t i o n was measured a f t e r 14 days and the f i g u r e s were c o r r e c t e d f o r endogenous e x c r e t i o n . A b s o r p t i o n data were expressed i n per cent and absolute amount absorbed.

J u s t i f i c a t i o n of comparison of per cent a b s o r p t i o n f i g u r e s can only be done i f the z i n c contents of the meals are i d e n t i c a l . When meals of d i f f e r e n t z i n c contents are compared i t i s necessary t o express the a b s o r p t i o n i n terms of absolute amounts of z i n c absorbed.


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Chemical methods The t o t a l z i n c content was determined by atomic a b s o r p t i o n spectrophotometry ( P e r k i n Elmer Model 360), a f t e r dry-ashing a t 500°C. The c a l c i u m a n a l y s i s was a l s o done by atomic a b s o r p t i o n spectrophotometry, but a f t e r wet-ashing i n s u l p h u r i c a c i d and hydrogen peroxide. N i t r o g e n a n a l y s i s was performed by a m i c r o - K j e l d a h l technique i n a Technicon Autoanalyser. P h y t i c a c i d determinations were performed by a m o d i f i c a t i o n of the procedure d e s c r i b e d by H o l t (16, 1 7 ) . The r a d i o a c t i v i t y i n each i n d i v i d u a l p o r t i o n of bread was measured i n the whole-body counter before s e r v i n g . TABLE I

Meal no and composition 1. White bread

Composition of the meals. Zinc content Zn a b s o r p t i o n (mg) Total Added % mg

0.4

38.2 (29.9-52.0)

a

b

0.15 (0.12-0.21)

2. White bread

3.6

3.1

13.2 (8.7-24.2)

0.48 (0.31-0.87

3. White bread, m i l k , cheese

3.3

1.1

15.7 (6.9-25.3)

0.52 (0.23-0.83)

16.6 (19.1-23.2)

0.22 (0.12-0.30)

4. Whole f l o u r bread 1.3

-


2.2

8.2 (5.7-11.3)

0.29 (0.20-0.40)

6. Whole f l o u r bread 3.1 milk

1.0

9.9 (5.6-14.4)

0.31 (0.17-0.45)

7. Whole f l o u r bread 3.2 beef

0.8

10.6 (6.0-15.6)

0.34 (0.19-0.50)

14.0 (8.7-21.8)

0.45 (0.28-0.70)

14.8 (10.0-22.9)

0.52 (0.35-0.80)

16.8 (10.7-26.3)

0.59 (0.37-0.92)

8. Whole f l o u r bread 3.2 cheese, m i l k 9. Whole f l o u r bread 3.5 egg, m i l k 10. Whole f l o u r bread 3.5 cheese,milk,casein Mean Range

a

-

0.4

-

b



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R e s u l t s and d i s c u s s i o n The composition of 10 d i f f e r e n t meals are shown i n Table I . This t a b l e a l s o i n c l u d e s the z i n c content, the per cent absorpt i o n and the absolute amount absorbed. As can be seen, there i s a s i g n i f i c a n t l y higher per cent a b s o r p t i o n i n meals c o n s i s t i n g of white bread (low e x t r a c t i o n rate) than i n meals c o n s i s t i n g of whole f l o u r bread, 38.2% versus 16.6%. The amount of z i n c was however c o n s i d e r a b l y h i g h e r i n whole f l o u r bread (1.3 mg versus 0.4 mg), which causes a higher absolute a b s o r p t i o n of z i n c from whole f l o u r bread. (0.22 mg versus 0.15 mg). When these two types of bread were enriched w i t h z i n c c h l o r i d e , r e s u l t i n g i n a z i n c content of 3.6 mg and 3.5 mg r e s p e c t i v e l y , an increased a b s o r p t i o n was found i n both of breads. The a b s o r p t i o n however was h i g h e r from the enriched white bread than from the enriched whole f l o u r bread. (0.48 mg (13.2%) versus 0.29 mg ( 8 . 2 % ) ) . Consequently i f the white bread i s e n r i c h e d w i t h z i n c t h i s could be a b e t t e r z i n c source than whole f l o u r bread enriched t o the same l e v e l . TABLE I I Zn-absorption from meals w i t h d i f f e r e n t p r o t e i n content Zn content (mg) Meal no and composition 2. White bread

Protein content (g)

T o t a l Added

3.6

5. White f l o u r bread 3.5

%

mg

3.1

5.2

13.2 (8.7-24.2)

0.48 (0.31-0.87)

2.2

6.0

8.2 (5.7-11.3)

0.29 (0.20-0.40)

19.3

14.0 (8.7-21.8)

0.45 (0.28-0.70)

26.7

0.59 16.8 (10.7-26.3) (0.37-0.92)


10. Whole f l o u r bread 3.5 cheese, m i l k , c a s e i n

Zn a b s o r p t i o n

_

When adding animal p r o t e i n i n the form of m i l k , egg and cheese t o the whole f l o u r meal, the z i n c a b s o r p t i o n was i n c r e a s e d . (Table I I ) . I t seems l i k e the b i n d i n g of z i n c t o p h y t i c a c i d and fibercomponents i s overcome i f enough animal p r o t e i n i s served together w i t h the whole f l o u r bread. The p r o t e i n content of whole f l o u r bread meal w i t h 3.5 mg z i n c i s 6 g and the a b s o r p t i o n i s 0.29 mg (8.2%). By i n c r e a s i n g the p r o t e i n content t o 19.3 g cheese and m i l k and keeping the same z i n c content, the a b s o r p t i o n increased t o 0.45 mg (14%).


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By i n c r e a s i n g the p r o t e i n content f u r t h e r t o 26.7 g w i t h the z i n c c o n c e n t r a t i o n s t i l l at 3.5 mg, the absorbed amount of z i n c was 0.59 mg (16.8%). TABLE I I I Zn a b s o r p t i o n from meals w i t h d i f f e r e n t Ca content


Zn content (mg) Meal Total no and composition

P r o t e i n Calcium

Added

gr

mg


%

mg

5. Whole f l o u r bread

3.5

2.2

6.0

19

8.2 0.29 (5.7-11.3) (0.20-0.40)

6. Whole f l o u r bread, m i l k

3.1

1.0

12.6

292

9.9 0.31 (5.6-14.4) (0.17-0.45)

7. Whole f l o u r bread, beef

3.2

0.8

12.6

23

10.6 0.34 (6.0-15.6) (0.19-0.50)

In animal experiments i t has been shown that a h i g h c a l c i u m content i n combination w i t h the p h y t i c a c i d i n whole f l o u r bread w i l l decrease the z i n c a b s o r p t i o n ( 1 0 ) . When adding m i l k and m i l k products to the whole f l o u r bread i n Dr. Sandstr0ms experiments the same p o s i t i v e e f f e c t was seen from the p r o t e i n despite of the h i g h e r c a l c i u m content (Table I I I ) . Meal no. 6 and no. 7 are showing t h i s e f f e c t , the p r o t e i n content i s i n both meals 12.6 g, while the Ca content i n no 6 i s about 10 times as h i g h as i n no. 7. The z i n c a b s o r p t i o n however TABLE IV Zn a b s o r p t i o n from white bread and d i f f e r e n t p r o t e i n content Zn content (mg) Meal no and composition

Protein

Total

Added

gr


%_

mg

2.

White bread

3.6

3.1

5.2

13.2 0.48 (8.7-24.2) (0.31-0.87)

3.

White bread cheese, m i l k

3.3

1.1

18.6

15.7 0.52 (6.9-25.3) (0.23-0.83)



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i s almost the same 9.9% and 10.6%, which i n both case are higher than without p r o t e i n (8.2%). No increase i n z i n c a b s o r p t i o n was seen when p r o t e i n was added to the white bread meals. (Table I V ) . I t ,is p o s s i b l e that the p r o t e i n competes w i t h the b i n d i n g to p h y t i c a c i d or f i b e r components i n whole f l o u r bread r a t h e r than f a c i l i t a t i n g z i n c a b s o r p t i o n . In c o n c l u s i o n , the b i n d i n g of the z i n c due to whole f l o u r bread i s not a serious problem i n a d i e t w i t h a low bread and a high p r o t e i n content such as i n normal d i e t s of people i n industrialized countries. By i n c r e a s i n g the fermentation p e r i o d when making the dough f o r the bread, the decreased z i n c absorption i n whole f l o u r bread can be overcome. The p h y t i c a c i d i s i n t h i s way broken down, and the z i n c b e t t e r a v a i l a b l e a b s o r p t i o n . In Table V i s shown the Zn absorption of the meals a f t e r d i f f e r e n t fermentation on p e r i o d s . The meals were b r e a k f a s t meals, composed of sour m i l k , white bread and bran or bread w i t h bran i n i t . TABLE V Zn a b s o r p t i o n from bread with d i f f e r e n t fermentation period Zn (mg)

Sour m i l k , white bread

Phytic acid mol

Zn absorption % mg (X-SD)

1.9

500

9.6^1.5

0.18^0.03

Sour m i l k bread w/ bran yeast 45 min« 1.8

420

11.9-2.5

0.21-0.04

Sour m i l k bread w/ bran yeast 15 h + 45 m i n d . 8

100

19.8-4.9

0.35-0.08

This could be of importance i n c o u n t r i e s where whole f l o u r bread i s a main component i n the d i e t and the supply of animal protein i s limited. Conclusion Most of our knowledge about f a c t o r s a f f e c t z i n c a b s o r p t i o n (2.» i£» 18) comes from s t u d i e s on animals. The most extensive s t u d i e s are made on the a f f e c t of p h y t i c a c i d , which i s present i n vegetables and u n r e f i n e d c e r e a l products. Decreased z i n c abs o r p t i o n has been found both when s u b s t a n t i a l amounts of sodiumphytate are added to the d i e t and when the d i e t s are based on p h y t i c - c o n t a i n i n g food, such as soy beans. The e x p l a n a t i o n of t h i s i s that a complex between Zn and p h y t i c a c i d i s made, r e s u l t i n g i n a decreased b i o a v a i l a b i l i t y .


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In human s t u d i e s done w i t h leavened and unleavened whole g r a i n bread (7, 19), the conclusions drawn were the same to those drawn f o r animal s t u d i e s . The importance of p h y t i c a c i d was l a t e r questioned by the same authors and decreased absorption was described to the f i b e r content i n the d i e t s (20) . A negative z i n c balance was a l s o a c r i b e d to the f i b e r content when a d i e t c o n t a i n i n g f r u i t s and vegetables (21) . Contrary to t h i s i s a study where z i n c balance was not a f f e c t e d even w i t h a high content of d i e t a r y f i b e r (22), where animal p r o t e i n a l s o showed a positive correlation Even i f there i s a l o t of unanswered questions around b i o a v a i l a b i l i t y of z i n c from the d i e t , these s t u d i e s could give us important i n f o r m a t i o n f o r o b t a i n i n g an optimal z i n c a b s o r p t i o n from composite bread meals. F i r s t of a l l these s t u d i e s do not support a change from whole f l o u r bread to a more r e f i n e d bread with a lower z i n c con tente Even i f there i s a lower per cent a b s o r p t i o n of z i n c from whole f l o u r bread, the absolute amount of z i n c absorbed from the unrefined products i s h i g h e r , because of the considerable h i g h e r content of z i n c i n these products. When the two types of bread were enriched to the same z i n c l e v e l the absorption was higher from the white bread. I f the z i n c content of a meal based on whole f l o u r bread was increased i n the form of animal p r o t e i n as m i l k and m i l k products, the absorption increased to the same l e v e l as that from z i n c en r i c h e d white bread. Consequently the c o n c l u s i o n drawn from t h i s study shows that i n a mixed balanced meal the z i n c - b i n d i n g of whole f l o u r bread has n e g l i g a b l e n u t r i t i o n a l s i g n i f i c a n c e . Four f a c t o r s are of importance f o r the a b s o r p t i o n and u t i l i z a t i o n of a mineral from the d i e t i n humans:


0

1. 2· 3. 4.

The c o n c e n t r a t i o n of the mineral i n the d i e t The c o n c e n t r a t i o n of other minerals and n u t r i e n t s i n the d i e t The b i o a v a i l a b i l i t y of the mineral i n the d i e t . The i n d i v i d u a l person's need f o r the m i n e r a l .

There i s a l o t of unanswered and important questions around b i o a v a i l a b i l i t y ο I n the l i t e r a t u r e there i s a tendency to de s c r i b e upper l i m i t s f o r a v a i l a b i l i t y of the minerals i n the d i e t . Do the " b i o a v a i l a b i l i t i e s " represent r e l i a b l e measurements of the amount of these elements a v a i l a b l e f o r a b s o r p t i o n , or do they only give values f o r the average absorption f o r the p a r t i c u l a r circumstances of the s t u d i e s ? I s i t p o s s i b l e to describe upper l i m i t s f o r a v a i l a b i l i t i e s of minerals? Do we r e a l l y increase the absorbed and u t i l a z e d amount of a m i n e r a l by f o r t i f i c a t i o n w i t h the mineral i n question? Do we f o r g e t that there i s a cooperation between a l l the elements present i n the d i e t which determine the b i o a v a i l a b i l i t y ? An other important f a c t o r i s that the body might r e g u l a t e the absorption of the mineral a f t e r the body's own need.



220


The s i g n i f i c a n c e of d i f f e r e n t i n h i b i t o r s i n the d i e t are the most common way t o study the b i o a v a i l a b i l i t y of a m i n e r a l . The i n h i b i t o r s of greatest consequence i n our d i e t i s as mentioned e a r l i e r f i b e r and p h y t i c a c i d . As important as studying these i n h i b i t o r s s i g n i f i c a n c e i n a mineral d e f i c i e n c y s i t u a t i o n i t might be t o determine these components value as p r o t e c t i n g f a c t o r s i n t o x i c conditions. Might be the body's own r e g u l a t i o n system i s put out of f u n c t i o n when a m i n e r a l i s given i n pure form without a t the same time give an increased amount of other minerals and n u t r i e n t s . This i s one of the reasons why Norway has a very r e s t r i c t i v e f o r t i f i c a t i o n p o l i c y of foods. We t h i n k we can have a b e t t e r c o n t r o l over the intake of minerals without f o r t i f y i n g , r a t h e r than give d i e t a r y advice to v u l n e r a b l e groups i n the p o p u l a t i o n . Studies of z i n c a b s o r p t i o n from s i n g l e meals can be used to i d e n t i f y d i e t a r y f a c t o r s i n f l u e n c i n g the degree of a b s o r p t i o n . They can, however, only give suggestions f o r the importance of these f a c t o r s f o r the whole d i e t . Furthermore i t i s uncompletely known how the a b s o r p t i o n of z i n c i s r e g u l a t e d . W i l l the body compensate a low a b s o r p t i o n from one meal w i t h a higher absorption from the next? The only way t o overcome t h i s problem i s long term balance s t u d i e s To o b t a i n complete z i n c balance i t i s important to i n c l u d e a l l components which might give l o s s e s Losses from the s k i n are seldom included i n these types of s t u d i e s , and as a consequence i t i s d i f f i c u l t t o t a l k about true balance. What i s determined i s a r e l a t i v e balance. Most of the z i n c balance s t u d i e s published so f a r , are short term experiments, and i t i s t h e r e f o r e d i f f i c u l t t o draw any conclusions about the value of d i f f e r e n t d i e t s as complete z i n c balance i s probably not o b t a i n e d From the data obtained f o r z i n c a b s o r p t i o n i n the s t u d i e s presented here, the contents of z i n c , p r o t e i n and p h y t i c a c i d were u s e f u l i n e s t i m a t i n g the degree of z i n c a b s o r p t i o n . The main determinant, however, seems t o be the t o t a l z i n c content. For p r a c t i c a l use f o r the consumer could be concluded: The b i n d i n g of z i n c due t o whole-meal bread i s not a s e r i o u s problem i n a well-balanced d i e t w i t h a r e l a t i v e low bread and a high p r o t e i n content such as i n the normal d i e t s of people l i v i n g i n i n d u s t r i a l i z e d nations. 0

0

0

Literature Cited 1. Prasad, A. S. "Trace elements in human health and disease. I. Zinc and Copper"edited by A. S. Pasad. New York: Academic Press 1976, p. 1. 2. Anonymous, 1975. "On Norwegian nutrition and food policy". Whitebook to the Parliament, november 1975. The Royal Ministry of Agriculture, Oslo. 3. National Research Council. Food and Nutrition Board.


15.

4. 5. 6. 7.


8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

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Recommended Dietary Allowances, 9th Ed., National Academy of Sciences, Washington, D.C. 1980. Maleki, M. Iran. Ecol. Food Nutr. 1973, 2, 39. Prasad, A. S.; Miale Jr. Α.; Farid, Z.; Sandstead, Η. H.; Schulert, A. R. J. Lab. Clin. Med. 1963, 61, 537. Prasad, A. S.; Schulert A. R.; Niale Jr. Α.; Farid Z.; Sandstead, Η. H. Am. J. Clin. Nutr. 1963, 12, 437. Reinhold, J. G.; Hedayati, H.; Lahimgarzadeh, Α.; Nast, K. Ecol. Food Nutr. 1973, 2, 157. Ronaghy, Η. Α.; Moe, P. G.; Halsted, J. A. Am. J. Clin. Nutr. 1968, 21, 709. Davies, N. T.; Olpin, S. E. Br. J. Nutr. 1979, 41, 591. O'Dell, B. L. Am. J. Clin. Nutr. 1969, 22, 1315. Sandstrøm, B . ; Arvidson, B.; Cederblad, Å.; Bjørn-Rasmussen, E. Am. J. Clin. Nutr. 1980, 33, 739. Cook, J. D.; Layrisse, M.; Martinez-Torres, C.; Walker, R.; Monsen, E.; Finch, C. A. J. Clin. Invest. 1972, 51, 805. Hallberg, L . ; Bjørn-Rasmussen, E. Scand. J. Heamatol. 1972, 9, 193. Layrisse, M.; Martinez-Torres, C. Am. J. Clin. Nutr. 1972, 25, 401. Arvidson, B . ; Cederblad, Å.; Bjørn-Rasmussen, E.; Sandstrøm, B. Internat. J. Nucl. Med. Biol. 1978, 5, 104. Holt, R. J. Sci. Food Agric. 1955, 6, 136. Davies, N. T.; Reid, H. Br. J. Nutr. 1979, 41, 579. Davies, N. T.; Hristic, V.; Flett, A. A. Nutr. Dep. Int. 1977, 15, 207. Reinhold, J. G.; Nasr, K.; Lahimgarzadele, Α.; Hedayati, H. Lancet. 1973, 1, 283. Reinhold, J. G.; Ismail-Beigi, F.; Faradji, B. Nutr. Dep. Int. 1975, 12, 75. Kelsay, J. L . ; Jacob, R. Α.; Prather, E. S. Am. J. Clin. 1979, 32, 2307. Sandstead, H. H.; Munoz, J. M.; Jacob, R. Α.; Klevay, L. M.; Reck, S. J.; Logan, J r . , G. M.; Dintzis, F. R.; Inglett, G. E . ; Shuey, W. C. Am. J. Clin. Nutr. 1978, 31, 1980.

RECEIVED October

13, 1982


Zinc Absorption from Composite Meals - ACS Symposium Series (ACS

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