Nutritional Bioavailability of Zinc - American Chemical Society

9 Effect of Fiber and Oxalic Acid on Zinc Balance of Adult Humans

Downloaded by UNIV OF PITTSBURGH on February 19, 2016 | http://pubs.acs.org Publication Date: January 20, 1983 | doi: 10.1021/bk-1983-0210.ch009

JUNE L. KELSAY U.S. Department of Agriculture, Carbohydrate Nutrition Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, Beltsville, MD 20705

In a study of 12 men fed a diet containing fiber in fruits and vegetables, mean zinc balance was negative and significantly lower than that on a low fiber diet. The higher fiber diet included spinach, which is high in oxalic acid. In a second study, zinc balance was not negative when cauliflower, which is low in oxalic acid, replaced the spinach in the higher fiber diet. In a third study, zinc balance was negative and significantly lower on the higher fiber diet including spinach than on a low fiber diet including spinach, or on a higher fiber diet without spinach. The adverse effect of the higher fiber diet containing spinach was observed during the fourth week of the study, but not during the third week. Fiber components can bind zinc and other minerals, possibly rendering the minerals unavailable for absorption by the animal body (1_, 2:, 3) . The effect of fiber on zinc balance of human subjects was reviewed previously (4) and appears to be related to level and kind of fiber, level of zinc, other components of the diet, and length of study period. One of the dietary components which may affect zinc availability is oxalic acid. Oxalic acid is capable of combining with minerals to form salt complexes. Calcium and zinc form the least soluble salts with oxalic acid (5, 6). Spinach contains more oxalic acid than most foods (approximately 700 mg/100 g), and i t s effect on calcium availability has been studied rather extensively. Other green leafy vegetables also contain considerable amounts of oxalic acid, and the oxalic acid is concentrated more in the leaves than in the stalks (7). Rhubarb, some nuts, tea, and cocoa have also been found to contain oxalic acid in amounts greater than 200 mg/100 g food (7-11). A number of studies have been conducted on rats to evaluate This chapter not subject to U.S. copyright Published 1983 American Chemical Society In Nutritional Bioavailability of Zinc; Inglett, George E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


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the e f f e c t o f the i n c l u s i o n o f spinach i n t h e d i e t on calcium u t i l i z a t i o n (12). Many o f these s t u d i e s were conducted w i t h low c a l c i u m intakes and h i g h l e v e l s o f spinach i n t h e d i e t . Under these c o n d i t i o n s , when young r a t s were f e d spinach, growth and c a l c i u m i n bones decreased. Calcium r e t e n t i o n could be improved by adding e x t r a calcium, and was a l s o i n f l u e n c e d by the a v a i l a b i l i t y o f v i t a m i n D. Studies on the e f f e c t o f o x a l i c a c i d i n spinach on calcium balance i n humans have shown a small decrease o r no e f f e c t on c a l c i u m balance (12). However, when subjects were given t e s t meals o f e i t h e r Swiss chard (13) o r amaranth (.14, IS) , which are r i c h i n o x a l i c a c i d , u r i n a r y e x c r e t i o n o f calcium i n d i c a t e d t h a t the absorption o f calcium from these sources was l e s s than t h a t o f an equal amount o f calcium from m i l k . Absorption o f calcium from m i l k was a l s o reduced when given along w i t h amaranth (14). L i t t l e i n f o r m a t i o n i s a v a i l a b l e on the e f f e c t o f o x a l i c a c i d on z i n c b i o a v a i l a b i l i t y . I n one study, Welch e t a l . (16) f e d weanling r a t s z i n c - d e f i c i e n t d i e t s w i t h and without 0.75% sodium o x a l a t e . The r a t s were dosed o r a l l y w i t h z i n c - l a b e l e d spinach leaves o r z i n c - l a b e l e d z i n c s u l f a t e . D i e t a r y o x a l a t e enhanced the a v a i l a b i l i t y o f r a d i o a c t i v e z i n c from z i n c s u l f a t e , but had no e f f e c t on z i n c from spinach leaves. Absorption and r e t e n t i o n o f z i n c was greater from spinach leaves than from z i n c s u l f a t e . Experiments Three s t u d i e s were c a r r i e d out i n our l a b o r a t o r y i n coopera t i o n w i t h the Food, N u t r i t i o n , and I n s t i t u t i o n A d m i n i s t r a t i o n Department o f the U n i v e r s i t y o f Maryland. The purpose o f these s t u d i e s was t o determine mineral balances i n a d u l t human s u b j e c t s when f i b e r i n f r u i t s and vegetables was added t o the d i e t . Zinc was one o f the minerals determined. The e f f e c t s o f the d i e t c o n t a i n i n g f i b e r were compared w i t h those o f a low f i b e r d i e t i n which f r u i t and vegetable j u i c e s replaced the f r u i t s and veget a b l e s . I n the f i r s t study, spinach was i n c l u d e d i n the d i e t c o n t a i n i n g f i b e r i n f r u i t s and vegetables. I n t h e second study, c a u l i f l o w e r , which i s low i n o x a l i c a c i d , replaced the spinach. In t h e t h i r d study, spinach was i n c l u d e d i n the low f i b e r d i e t and i n a d i e t c o n t a i n i n g f r u i t s and vegetables; c a u l i f l o w e r was i n c l u d e d i n a second d i e t c o n t a i n i n g f r u i t s and vegetables. Study 1. Two d i e t s were f e d i n a crossover design t o 12 men 37 t o 58 years o f age (17) . During the f i r s t 26 days o f t h e study, s i x men consumed t h e higher f i b e r d i e t c o n t a i n i n g f r u i t s and vegetables and s i x men consumed the low f i b e r d i e t c o n t a i n i n g f r u i t and vegetable j u i c e s . At the end o f 26 days, the s u b j e c t s consumed the a l t e r n a t e d i e t f o r 26 days. A 2-day r e v o l v i n g menu comprised each d i e t . Foods i n c l u d e d i n the same amounts i n both d i e t s are given i n Table I . In Table I I are l i s t e d the foods and amounts f e d i n each o f the two d i e t s i n a d d i t i o n t o those i n

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

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Table I Foods Common t o Both D i e t s , 2800-Calorie L e v e l , Study 1


Day 1

Day 2

Puffed r i c e c e r e a l , 7.5 g M i l k , 366 g Bread, w h i t e , 78 g Egg, scrambled, 50 g B u t t e r , 42.3 g Cream, 90 g Sugar, 60 g Roast beef, 85 g Pudding, 130 g Ham, 85 g Salad d r e s s i n g , 48 g Cake, 53 g

M i l k , 366 g Bread, w h i t e , 103 g Bacon, b r o i l e d , 15 g B u t t e r , 28.2 g Cream, 90 g Sugar, 72 g T u n a f i s h , 78 g Mayonnaise, 28 g Ground beef, 113 g Salad d r e s s i n g , 32 g Ice cream, 66 g

Table I I A d d i t i o n s t o D i e t s , 2800-Calorie L e v e l , Study 1

Day 1

Grapefruit juice, 247 g Jelly, 25 g Sugar, 24 g

Pineapple 125 Vegetable 121 Macaroni, 105

Day 2 Higher f i b e r

Low f i b e r

juice, g juice, g g

Grape j u i c e , 253 g Milk, 122 g

Grapefruit, 200 g Dates, 80 g

Corn, 82 g Pineapple, 123 g Spinach, 102 g Carrots, 55 g Cabbage, 45 g

Blackberries, 252 g

Low f i b e r

Higher f i b e r

Orange j u i c e , 249 g Jelly, 25 g Sugar, 18 g

Apple j u i c e , 124 g Vegetable j u i c e , 121 g Macaroni, 140 g

Grape j u i c e , 253 g Milk, 122 g

Oranges, 200 g Raisins, 72 g

Peas, 85 g Apple, 160 g Broccoli, 92 g Squash, 120 g Lettuce, 30 g Tomato, 100 g Blueberries, 284 g



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Table I . These are the amounts f e d a t the 2800-calorie l e v e l . C a l o r i c i n t a k e was adjusted t o the i n d i v i d u a l needs o f the subj e c t s by i n c r e a s i n g o r decreasing a l l foods the appropriate percentage t o maintain each subject's weight during the study. Carbohydrate, f a t , and p r o t e i n made up 50, 37, and 13% o f t h e t o t a l c a l o r i e s , r e s p e c t i v e l y . The low f i b e r d i e t was supplemented w i t h carotene, i r o n , magnesium, and copper i n an attempt t o make the two d i e t s equivalent i n a l l respects except f i b e r . During the l a s t 7 days o f each 26-day p e r i o d , the subjects c o l l e c t e d a l l u r i n e and f e c a l samples. Feces were marked by g i v i n g each subject 50 mg B r i l l i a n t blue. Seven-day composites o f food, u r i n e , and feces were prepared. N e u t r a l detergent f i b e r (NDF) i n t a k e was 5 and 25 g/day on the low and higher f i b e r d i e t s , r e s p e c t i v e l y ( 1 8 ) . Bowel t r a n s i t time was computed as the time from i n g e s t i o n o f the marker u n t i l most o f the c o l o r appeared i n t h e f e c e s . T r a n s i t time decreased from a mean o f 52 hours on the low f i b e r d i e t t o a mean o f 38 hours on the higher f i b e r d i e t . The i n c l u s i o n o f f r u i t s and vegetables i n the d i e t a l s o increased f e c a l weight, number o f d e f e c a t i o n s , and f e c a l e x c r e t i o n s o f energy, n i t r o g e n , and f a t . Zinc intakes o f the subjects were 13.2 and 12.6 mg/day on the low and higher f i b e r d i e t s , r e s p e c t i v e l y (19). Fecal e x c r e t i o n s o f z i n c were 70 and 102% o f the i n t a k e on the low and higher f i b e r d i e t s , r e s p e c t i v e l y (Figure 1 ) . The mean z i n c balance was p o s i t i v e on the low f i b e r d i e t and negative on the higher f i b e r d i e t , and these balances d i f f e r e d s i g n i f i c a n t l y from each other. The mean r e t e n t i o n o f z i n c on the low f i b e r d i e t was 3.5 mg/day, and the mean l o s s on the higher f i b e r d i e t was 0.9 mg/day (Figure 2 ) . These r e s u l t s i n d i c a t e d t h a t i n c r e a s i n g the f i b e r i n the d i e t might r e s u l t i n negative balances o f z i n c , and appeared t o confirm r e s u l t s o f some e a r l i e r s t u d i e s which were reviewed p r e v i o u s l y (£>· Study 2. The purpose o f t h i s study was t o determine the e f f e c t o f d i f f e r e n t l e v e l s o f f i b e r i n the d i e t on mineral b a l ances. Four d i e t s were f e d t o 12 men 35 t o 49 years o f age ( 2 0 ) . A l l s u b j e c t s consumed a l l d i e t s f o r 21 days each i n a 4 X 4 L a t i n square design. D i e t s 1 and 3 were s i m i l a r t o the low and higher f i b e r d i e t s o f study 1, except t h a t a t h i r d menu, designed t o c o n t a i n the same amounts o f n u t r i e n t s and f i b e r as those i n study 1, was r o t a t e d w i t h the other two. A l s o , c a u l i f l o w e r replaced the spinach i n the day 1 menu f o r d i e t 3. D i e t 2 contained 1/2 and d i e t 4 contained 1 1/2 the amounts o f f r u i t s and vegetables o f d i e t 3, and these two d i e t s a l s o had 3-day r e v o l v i n g menus. As an example, the foods and amounts f e d a t the 2800-calorie l e v e l f o r the day 3 menu are l i s t e d i n Tables I I I and IV. Menus f o r days 1 and 2 f o r d i e t s 2 and 4 were adjusted f o r i n t a k e s o f f r u i t s and vegetables i n a manner s i m i l a r t o those f o r day 3. C a l o r i c i n t a k e s were adjusted by i n c r e a s i n g o r decreasing a l l foods the appropriate percentage t o maintain each subject's weight during



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Figure 1. Zinc excretion as percentage of intake, study 1 (19).



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Figure 2. Zinc intake and excretion, study 1. Dietary intake is indicated by the top of the bar. The length of the vertical bar represents total excretion in urine and feces. Balance is indicated by the bottom of the bar. When the bottom of the bar is above the zero line, the balance is positive. When the bottom of the bar is below the zero line, the balance is negative.


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Table I I I


Foods Common t o A l l D i e t s , 2800-Calorie L e v e l , Day 3, Study 2

Egg, 50 g

Bread, w h i t e , 50 g

B u t t e r , 52 g

Cream, 90 g

Pork chop, 85 g

Mayonnaise, 14 g

Ice cream, 66 g

Turkey, 75 g

Cookies, 25 g

Table IV A d d i t i o n s t o D i e t s , 2800-Calorie L e v e l , Day 3, Study 2

Orange j u i c e Oranges Figs, dried Bread Maple s i r u p Milk Sugar Apple j u i c e Pears B r u s s e l s sprouts Vegetable j u i c e Asparagus Rice Cranberry j u i c e Cranberries Apples Raisins B u t t e r s c o t c h pudding Pumpkin pudding Cookies

Diet 3

Diet 4

200 75 28 39 122 36

300 113

155 78

233 116

48

95

143

24 25 25 65 91

48 50 50

72 75 75

182 10

273

Diet 1

Diet 2

g

g

249

124 100 38 28 39 305 96 62 78 39

28 39 366 84 124

121 124 100

130



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the study. Carbohydrate, f a t , and p r o t e i n made up 50, 37, and 13% o f the t o t a l c a l o r i e s , r e s p e c t i v e l y , and were s i m i l a r on a l l f o u r d i e t s . Carotene, i r o n , magnesium, and copper were not added t o the low f i b e r d i e t as i n study 1, because we f e l t t h a t the unsupplemented i n t a k e s would be more r e p r e s e n t a t i v e o f the l e v e l s o f i n t a k e on a low f i b e r d i e t . The number o f d e f e c a t i o n s increased as the f i b e r i n t h e d i e t i n c r e a s e d . The increase was from 7 per week on t h e low f i b e r d i e t to 11 per week on the highest f i b e r d i e t ; however, mean t r a n s i t time on a l l d i e t s was about 30 hours. Both wet and d r y f e c a l weights increased as the f i b e r i n the d i e t i n c r e a s e d . Fecal e x c r e t i o n s o f energy, n i t r o g e n , and f a t increased as the l e v e l o f f i b e r i n the d i e t increased. Mean z i n c intakes on t h e four d i e t s ranged from 11.8 t o 12.4 mg/day. F e c a l e x c r e t i o n s o f z i n c were 73, 74, 81, and 84% o f t h e i n t a k e on d i e t s 1 t o 4, r e s p e c t i v e l y , and t h e percent e x c r e t i o n on d i e t 4 was s i g n i f i c a n t l y higher than those on d i e t s 1 and 2 ( F i g u r e 3 ) . Zinc balance was s i g n i f i c a n t l y lower on d i e t 4 than on d i e t s 1 and 2, and r e t e n t i o n s on the f o u r d i e t s were 2.8, 2.9, 2.1, and 1.5 mg/day f o r d i e t s 1 t o 4, r e s p e c t i v e l y (Figure 4 ) . The reason f o r t h e d i f f e r e n c e s i n z i n c balances between these two s t u d i e s was not c l e a r . I n an e f f o r t t o determine i f t h e o x a l i c a c i d i n spinach i n the f i r s t study could be r e s p o n s i b l e f o r a t l e a s t p a r t o f the decrease i n b i o a v a i l a b i l i t y o f z i n c i n t h e f i r s t study, we determined o x a l i c a c i d content o f f e c e s . Mean o x a l i c a c i d e x c r e t i o n i n feces when the subjects were on t h e h i g h e s t f i b e r d i e t i n study 2 was about 1/2 t h a t on the h i g h e r f i b e r d i e t i n study 1 (210 and 423 mg/day, r e s p e c t i v e l y ) . Another f a c t o r which might help e x p l a i n the r e s u l t s was the length o f the d i e t a r y p e r i o d s ; t h e d i e t a r y p e r i o d s i n study 1 were 5 days longer than i n study 2. Study 3. Because o f t h e c o n f l i c t i n g r e s u l t s o f t h e f i r s t two s t u d i e s w i t h regard t o mineral balances, we c a r r i e d out a t h i r d study t o i n v e s t i g a t e the separate and combined e f f e c t s o f f i b e r and o x a l i c a c i d , as w e l l as length o f study p e r i o d on mineral balances. Twelve men 34 t o 58 years o f age consumed three d i e t s f o r 28 days each i n a 3 X 3 L a t i n square design (21). D i e t 1 was s i m i l a r to t h e low f i b e r d i e t f e d i n the f i r s t study, w i t h the f o l l o w i n g m o d i f i c a t i o n s : Spinach was i n c l u d e d i n the d i e t every other day and b r o c c o l i was included on a l t e r n a t e days; o n l y 1/2 cup o f m i l k was given w i t h the evening meal i n place o f 1 cup as i n t h e f i r s t study, i n order t o e q u a l i z e the amount o f calcium a v a i l a b l e w i t h the spinach meal i n d i e t s 1 and 2; carotene, i r o n , magnesium, and copper were not added t o the d i e t as i n the f i r s t study. D i e t 2 contained f i b e r i n f r u i t s and vegetables and was the same as the higher f i b e r d i e t i n the f i r s t study, i n c l u d i n g spinach every other day and b r o c c o l i on a l t e r n a t e days. D i e t 3 was t h e same as d i e t 2 except t h a t c a u l i f l o w e r replaced the spinach. On a l l three



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Figure 3. Zinc excretion as percentage of intake, study 2 (20).



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Figure 4. Zinc intake and excretion, study 2. Dietary intake is indicated by the top of the bar. Balance is indicated by the bottom of the bar.


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d i e t s , 1 cup o f m i l k was given with b r e a k f a s t and 1/2 cup w i t h dinner. During weeks 3 and 4 o f each 28-day p e r i o d , a l l u r i n e and feces were c o l l e c t e d . Two 7-day composites o f food, u r i n e , and feces were prepared. Bowel t r a n s i t times were not s i g n i f i c a n t l y d i f f e r e n t on the three d i e t s during week 3, but the mean t r a n s i t times o f 33 and 30 hours on the two higher f i b e r d i e t s were s i g n i f i c a n t l y lower than t h a t o f 43 hours on the low f i b e r d i e t during week 4. The number o f d e f e c a t i o n s and wet and dry f e c a l weights were s i g n i f i c a n t l y h i g h e r on the d i e t s c o n t a i n i n g f i b e r than on the low f i b e r d i e t during both weeks 3 and 4. Mean z i n c intakes ranged from 10.7 to 12.3 mg/day. Fecal z i n c as a percent of intake on d i e t s 1, 2, and 3 during week 3 was 95, 83, and 88%, and these values were not s i g n i f i c a n t l y d i f f e r e n t from each other (Figure 5 ) . Zinc balances during week 3 were 0.0, 1.7, and 0.7 mg/day on d i e t s 1, 2, and 3, r e s p e c t i v e l y , and were not s i g n i f i c a n t l y d i f f e r e n t from each other (Figure 6 ) . During week 4, f e c a l z i n c as a percent o f intake was 77, 105, and 91% on d i e t s 1, 2, and 3, r e s p e c t i v e l y , and was s i g n i f i c a n t l y h i g h e r on d i e t 2 than on d i e t s 1 and 3 (Figure 7). Zinc balances during week 4 were 2.0, -1.4, and 0.4 mg/day on d i e t s 1, 2, and 3, r e s p e c t i v e l y , and the balance on d i e t 2 was s i g n i f i c a n t l y lower than those on d i e t s 1 and 3 (Figure 8). Discussion

and

Conclusions

R e s u l t s of the t h i r d study i n d i c a t e t h a t the negative z i n c balances were a r e s u l t of the combination o f o x a l i c a c i d and f i b e r i n the same d i e t . With the l e v e l and k i n d o f f i b e r and the l e v e l o f z i n c f e d , f i b e r alone d i d not have an adverse e f f e c t on z i n c balance. There was a decrease i n z i n c balance on the h i g h e s t f i b e r d i e t i n study 2; however, the balance was p o s i t i v e . With the l e v e l o f z i n c f e d , a g r e a t e r e f f e c t might have been seen w i t h l e v e l s of f i b e r higher than the ones f e d . Some o f the subjects complained of the l a r g e r amounts of watery feces when they consumed the highest f i b e r d i e t i n study 2. However, w i t h an extended p e r i o d o f time on t h i s d i e t they might have become adjusted and excreted s t o o l s w i t h a f i r m e r c o n s i s t e n c y . A l s o , an extended p e r i o d of time might have r e s u l t e d i n f u r t h e r decreases i n z i n c balance. Bowel t r a n s i t times, number o f d e f e c a t i o n s , f e c a l weights, and f e c a l excretions of energy, n i t r o g e n , and f a t were not r e l a t e d t o z i n c balances, but were r e l a t e d t o l e v e l o f f i b e r intake. F u r t h e r i n v e s t i g a t i o n i s needed on the combined e f f e c t s o f o x a l i c a c i d and f i b e r . In v i t r o studies could provide clues t o the nature of the b i n d i n g o f minerals to o x a l i c a c i d and f i b e r : whether o x a l i c a c i d and f i b e r each binds p a r t o f the z i n c , o r whether there i s a f i b e r - z i n c - o x a l a t e complex formed. Kojima et a l . (22) studied the i n v i t r o e f f e c t o f spinach on the s o l u b i l i z a t i o n of i r o n p r e v i o u s l y s o l u b i l i z e d from cooked



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Figure 5. Zinc excretion as percentage of intake, week 3, study 3.


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Figure 6. Zinc intake and excretion, week 3, study 3. Dietary intake is indicated by the top of the bar. Balance is indicated by the bottom of the bar.



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Figure 7. Zinc excretion as percentage of intake, week 4, study 3.


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Figure 8. Zinc intake and excretion, week 4, study 3. Dietary intake is indicated by the top of the bar. Balance is indicated by the bottom of the bar.



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p i n t o bean suspension. T o t a l s o l u b l e i r o n was decreased by 7% when spinach supernatant was added, by 50% when spinach r e s i d u e was added, and by 80% when whole spinach was added. The i n v e s t i gators concluded t h a t "spinach supernatant contains f a c t o r s which b i n d i r o n and increase the a f f i n i t y f o r a s s o c i a t i o n w i t h the i n s o l u b l e spinach r e s i d u e " . At l e a s t one o f these f a c t o r s could be o x a l i c a c i d . However, Van Campen and Welch (23) reported t h a t i n r a t s i r o n was e q u a l l y a v a i l a b l e from spinach, i r o n o x a l a t e , and FeClg, and t h a t the a d d i t i o n o f 0.75% o x a l a t e t o the d i e t appeared t o enhance i r o n u t i l i z a t i o n . Since we d i d not f i n d adverse e f f e c t s on z i n c balance by the h i g h e r f i b e r d i e t c o n t a i n i n g spinach u n t i l the f o u r t h week o f study 3, balance s t u d i e s should be c a r r i e d out f o r longer p e r i o d s o f time t o determine i f negative z i n c balances p e r s i s t . Perhaps i n the e a r l i e r s t u d i e s on e f f e c t s o f spinach on calcium balance o f human s u b j e c t s , more d e f i n i t i v e e f f e c t s would have been noted i f the spinach had been f e d along w i t h a higher f i b e r d i e t . Length o f study p e r i o d i s a l s o a l i k e l y f a c t o r , as some o f t h e s t u d i e s were c a r r i e d out f o r l e s s than 2 weeks. Negative mineral balances as a r e s u l t o f o x a l i c a c i d and f i b e r together i n the d i e t may not n e c e s s a r i l y be a problem, as i t i s not too l i k e l y t h a t spinach would be i n c l u d e d i n even a h i g h f i b e r d i e t as o f t e n as 3 o r 4 times a week. However, i t i s p o s s i b l e t h a t the frequent i n c l u s i o n o f foods c o n t a i n i n g o x a l i c a c i d i n the d i e t might be o f concern where d i e t s are high i n f i b e r and low i n mineral content. Singh e t a l . (24) reported t h a t the normal r u r a l d i e t i n the Udaipur r e g i o n o f I n d i a i s low i n o x a l i c a c i d but t h a t i t s i n t a k e r i s e s s h a r p l y i n the season when ama r a n t h , p u r s l a n e , pigweed, and spinach a r e abundant. I n t h a t r e g i o n , o x a l i c a c i d i n t a k e was c o n s i s t e n t l y higher f o r t h e upper income group than f o r t h e low income group. Tabekhia e t a l . (25) found a high l e v e l o f o x a l a t e i n r e l a t i o n t o calcium i n Jew's mallow and p u r s l a n e , which a r e two important l e a f y vegetables i n the Egyptian d i e t . F u r t h e r study o f the e f f e c t s o f d i f f e r e n t l e v e l s o f o x a l i c a c i d and f i b e r i n t a k e on mineral balances i s recommended.

Literature Cited 1. 2. 3. 4. 5. 6.

Reinhold, J . G.; Ismail-Beigi, F.; Faradji, B. Nutr. Rep. Int. 1975, 12, 75-85. Ismail-Beigi, F . ; Faradji, B.; Reinhold, J . G. Am. J . Clin. Nutr. 1977, 30, 1721-5. Camire, A. L.; Clydesdale, F. M. J . Food Sci. 1981, 46, 548-51. Kelsay, J . L. Cereal Chem. 1981, 58, 2-5. Hodgkinson, Α.; Zarembski, P. M. Calc. Tiss. Res. 1968, 2, 115-32. Weast, R. C.; Astle, M. J. "CRC Handbook of Chemistry and Physics"; 61 ed.; CRC Press, Inc.: Boca Raton, FL, 1980-81.


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KELSAY


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Kohman, E. P. J. Nutr. 1939, 18, 233-46. Majumdar, B. N.; De, Ν. Κ. Ind. J. Med. Res. 1938, 25, 671-5. Andrews, J. C.; Viser, Ε. T. Food Res. 1951, 16, 306-12. Zarembski, P. M.; Hodgkinson, A. Brit. J. Nutr. 1962, 16, 627-34. Kaul, S.; Verma, S. L. Ind. J. Med. Res. 1967, 55, 274-8. Gontzea, I . ; Sutzescu, P. "Natural antinutritive substances in foodstuffs and forages"; S. Karger: Basel, Switzerland, 1968. Walker, A. R. P.; Walker, B. F . ; Wadvalla, M. Ecol. Fd. Nutr. 1975, 4, 125-30. Pingle, U . ; Ramasastri, Β. V. Brit. J. Nutr. 1978, 39, 119-25. Pingle, U . ; Ramasastri, Β. V. Brit. J. Nutr. 1978, 40, 591-4. Welch, R. M.; House, W. A . ; Van Campen, D. J. Nutr. 1977, 107, 929-33. Kelsay, J. L.; Behall, K. M.; Prather, E. S. Am. J. Clin. Nutr. 1978, 31, 1149-53. Kelsay, J. L.; Goering, H. K.; Behall, Κ. M.; Prather, E. S. Am. J. Clin. Nutr. 1981, 34, 1949-52. Kelsay, J. L.; Jacob, R. Α.; Prather, E. S. Am. J. Clin. Nutr. 1979, 32, 2307-11. Kelsay, J. L.; Clark, W. M.; Herbst, B. J.; Prather, E. S. J. Agr. Food Chem. 1981, 29, 461-5. Kelsay, J. L.; Prather, E. S. Fed. Proc. 1981, 40, 854. Kojima, N . ; Wallace, D.; Bates, G. W. Am. J. Clin. Nutr. 1981, 34, 1392-1401. Van Campen, D. R.; Welch, R. M. J. Nutr. 1980, 110, 1618-21. Singh, P. P.; Kothari, L. K.; Sherma, D. C.; Saxena, S. N. Am. J. Clin. Nutr. 1972, 25, 1147-52. Tabekhia, M. M.; Toma, R. B . ; El-Mahdy, A. R. Nutr. Rep. Int. 1978, 18, 611-6.

RECEIVED October

13, 1982


Nutritional Bioavailability of Zinc - American Chemical Society

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