Bioavailability of Dietary Calcium - ACS Symposium Series (ACS

6 Bioavailability of Dietary Calcium Effect of Phytate on Adult Men Consuming Nonvegetarian Diets

Downloaded by UNIV OF LIVERPOOL on November 12, 2016 | http://pubs.acs.org Publication Date: April 2, 1985 | doi: 10.1021/bk-1985-0275.ch006

EUGENE R. MORRIS and REX ELLIS Beltsville Human Nutrition Research Center, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705 Two metabolic balance studies were conducted using healthy adult men to study the effect of phytate on bioavailability of dietary calcium. Dietary treatments were each 15 days in duration. In the first study, a mean daily calcium balance of 208±58 (SD) mg was observed when 2.0 g of phytate from 36 g of whole wheat bran was consumed daily with 1100 mg of calcium, phytate/calcium molar ratio 0.11. Calcium balance was 184±87 mg when 36 g of dephytinized bran was consumed with the same intake of calcium, phytate/calcium molar ratio 0.01. In the second study, calcium intake was 740 mg/day. Apparent absorption (intake minus fecal excretion) of calcium decreased when the diet contained muffins with added sodium phytate to increase the molar ratio of phytate/calcium from 0.04 to 0.14 and 0.24. One-half of the men excreted more calcium in feces than was consumed when the high phytate diet was consumed. People consuming diets with molar ratios of phytate/calcium exceeding 0.2 may be at risk of calcium deficiency because of low bioavailability of dietary calcium unless physiological adjustments can be accomplished that maintain homeostasis. Phytate from plant products i s generally considered to decrease b i o a v a i l a b i l i t y of dietary calcium to humans (1). Most human studies investigating the effect of phytate on calcium b i o a v a i l a b i l i t y have used wheat bran or high extraction wheat flour as the source of phytate. Reinhold et a l . (2) observed greater negative calcium balances by adult men consuming unleavened whole meal bread compared to the same amount of phytate as sodium phytate i n a low f i b e r bread. With the p o s s i b i l i t y therefore, that there may be an effect of dietary fiber on calcium b i o a v a i l a b i l i t y , studies are needed to c l a r i f y whether the phytate or dietary fiber component of wheat bran i s the responsible agent decreasing calcium b i o a v a i l ability. This chapter not subject to U.S. copyright. Published 1985 American Chemical Society

Kies; Nutritional Bioavailability of Calcium ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

64

NUTRITIONAL BIOAVAILABILITY OF CALCIUM

Two metabolic balance studies conducted i n our laboratory have yielded information r e l a t i v e to the e f f e c t o f phytate and dietary fiber on calcium b i o a v a i l a b i l t y . In the f i r s t study, a r e l a t i v e l y high intake of dietary fiber was consumed with a 10-fold difference in phytate intake from wheat bran. In the second study three levels of phytate were consumed with a low amount of dephytinized bran as the p r i n c i p a l dietary fiber source. The two higher phytate levels i n the l a t t e r study were attained using sodium phytate. Materials and Methods


Balance study protocols The two human diet studies w i l l be designated HS-I and HS-II. The f i r s t study (HS-I) was 30 days i n duration. Ten adult men i n good health ranging i n age from 23 to 48 years were subjects. The menus consisted o f foods routinely consumed i n the United States and repeated i n 5-day cycles (3_). The diet treatments were l e v e l of phytate intake, either 0.2 or 2.0 g/day. Each l e v e l was consumed for 15 days, three consecutive repeats of the 5-day menu cycle. To provide 2.0 g/day of phytic acid, 36 g of wheat bran was baked into 6 muffins and two muffins were eaten each meal. Dephytinized bran was prepared by incubating the bran i n water and allowing the endogenous phytase to hydrolyze the phytate, then the entire incubation mixture was freeze-dried (4) and 36 g baked into 6 muffins. Thus, the intake of a l l nutrients and neutral detergent f i b e r was the same for both phytate intakes. Five subjects consumed the whole bran muffins for 15 days followed by the dephytinized bran muffins for 15 days and the other 5 subjects i n the reverse order. B r i l l i a n t blue dye was given at breakfast on the f i r s t day of each c o l l e c t i o n period to aid i n demarcation of stools. Stool composites were made for days 1-5, 6-15, 16-20 and 21-30 and urine composites for days 6-15, and 21-30. Daily food composites were made, homogenized, freeze-dried and then analyzed to determine mineral nutrient intakes. Twelve adult men participated i n the second study (HS-II). The diet treatments consisted of three d i f f e r e n t phytate intakes. A three period crossover design was used i n which each sequence was repeated the same number of times (Table I ) . A repeating 5-day menu cycle was again used and each dietary treatment was 15 days in duration, t o t a l time for the study was 45 days. Muffins, two each meal, contained 8.65 g of the water insoluble f r a c t i o n of dephytinized bran per day, derived from 12 g of whole wheat bran. The muffin ingredients, including the dephytinized bran, provided about 0.3 g of phytate per day. Sodium phytate (Sigma Chemical Co., St. Louis, MO) was added to the muffins to provide two higher intakes of phytate. The other menu items contributed about 0.2 g of phytate per day. B r i l l i a n t blue dye was again administered to aid i n demarcation of stools. Urine and feces were collected throughout the entire study and composites were made from each 5 days.


6. MORRIS AND ELLIS

Effect of Phytate on Adult

Table I . Study Days

Study Design f o r HS-II

Diet Treatment Assignment (12 subjects)

(2) A Β C

1-15 16-30 31-45

65

Men

(2) A C Β

(2) Β A C

(2) Β C A

(2) C A Β

(2) C Β A


Note: Menus r e p e a t e d i n 5-day c y c l e s . D i e t t r e a t m e n t s were p h y t i c a c i d i n t a k e , g/day, A, 0.5; B, 1.7; and C, 2.9.

Concurrently with HS-II, 6 additional men consumed the low phytate menus f o r 45 days, 9 consecutive repeats of the 5-day menu cycle. This study w i l l be designated HS-III i n the following section. The non-muffin food items were provided i n increments as needed to maintain volunteer's weight + 2 kg during each of the three studies. For one week prior to and following the 45-day controlled diet period o f HS-II and HS-III, each i n d i v i d u a l collected duplicate portions of a l l food and l i q u i d s consumed. These self-selected diets were brought to the laboratory and daily composites were prepared for analysis. The wheat bran used i n these studies was milled for us from a single l o t of Waldron hard red spring wheat. Other foods and diet ingredients were purchased from l o c a l food suppliers. Data from HS-I was analyzed s t a t i s t i c a l l y by Student's paired t test, each subject acting as his own control. A three-way analysis of variance (ANOVA) was performed to test for s i g n i f i c a n t differences betwen diet treatments, periods and individuals i n HS-II and HS-III. Phytate analysis of muffins, diet composites and stools was performed by a modification of the f e r r i c ion p r e c i p i t a t i o n method for HS-I (5) and by an ion exchange method for HS-II and - I I I (6). Calcium was determined by atomic absorption spectrophotometry. HS-I diet and f e c a l samples were dry ashed and HS-II and - I I I samples were prepared by a combination dry-wet ashing procedure ( H i l l et a l . unpublished). The approved method of American Association of Cereal Chemists (7) was used for determining neutral detergent f i b e r . Results Dietary intake data for calcium, phytate and phytate/calcium r a t i o are summarized i n Table I I . Mean calcium intake for HS-I was about 300 mg greater than the recommended dietary allowance (RDA) of 800 mg established f o r adults by the National Research Council (8) and for HS-II just s l i g h t l y less than the RDA. The range of calcium intakes, because of d i f f e r e n t c a l o r i c needs was from 927 to 1490


NUTRITIONAL BIOAVAILABILITY O F C A L C I U M

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Table I I .

Summary of D i e t a r y I n t a k e s

Calcium

Phytate

mg/day

g/day

molar r a t i o HS-I

1090 1150

Phy ta te /Ca le ium

1

2

0.11 0.01

2.0 0.2


HS-II3 740 740 740

0.5 1.7 2.9

0.04 0.14 0.24

1

As phytic acid. Ten subjects, means for 15 days. ^Twelve subjects, means for 15 days. Intakes of HS-III (6 subjects) same as low phytate d i e t . 2

for HS-I and 620 to 910 for HS-II. Phytate intakes were essen t i a l l y constant across individuals because almost a l l of the phytic acid was present i n the muffins and each individual ate two muffins each meal regardless of c a l o r i c needs. In HS-I there was a 10-fold difference i n the two phytate intakes and the resultant phytate to calcium molar r a t i o s . The highest phytate intake during HS-II was only 0.9 g/day greater than HS-I, but the intermediate and high phytate/calcium molar ratios were greater than for HS-I. HS-I. Metabolic balance data for HS-I are summarized in Table III. For the f i r s t 5 days of each diet treatment, A i n Table III, about 100 mg more of calcium was excreted i n the feces when whole bran muffins were consumed compared to dephytinized bran muffins. Consequently, apparent absorption was greatest, Ρ

Bioavailability of Dietary Calcium - ACS Symposium Series (ACS

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