11 Dietary Phytate/Zinc Molar Ratio and Zinc Balance in Humans
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EUGENE R. MORRIS and R E X ELLIS U.S. Department of Agriculture, Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville Agricultural Research Center, Beltsville, MD 20705
The effect on zinc balance of a 10-fold difference in dietary molar ratio of phytate/zinc was tested i n a metabolic balance study with 10 adult men. The mean zinc balance was 2.74 mg per day when the dietary molar ratio of phytate/zinc was about 12 and 2.0 mg per day when the r a t i o was about 1. Menus consisted of foods commonly consumed i n the United States. The mean daily intake of zinc was 17 mg and of neutral detergent fiber 16 g. The molar ratios of phytate/zinc were attained by using 36 g per day of whole or dephytinized wheat bran. Analysis of hospital and self-chosen diets indicate that the majority of the United States population consume diets with molar ratios of phytate/zinc less than 10, but which provide less than the recommended dietary allowance of z i n c . The balance results are discussed i n relation to magnitude of the zinc intake, the type of food consumed and the role of adaptive responses i n maintaining adequate zinc nutriture. Zinc i s a required mineral nutrient i n the diet of animals and the signs and effects of a dietary deficiency have been described in several species (jL). Nutritional zinc deficiency has also been described i n humans (2). Signs of n u t r i t i o n a l zinc deficiency may be manifest even though the individual i s consuming an amount of dietary zinc that exceeds the usually designated requirement (3). Thus, b i o a v a i l a b i l i t y of dietary zinc i s a factor that must be evaluated i n considering adequacy of dietary intake (JO. Phytic acid and dietary fiber i n foods have been implicated as important determinants of dietary zinc b i o a v a i l a b i l i t y (5,.6,7). For rats, the molar ratio of phytic acid to zinc i s a good predictor of b i o a v a i l a b i l i t y of dietary zinc when semipurified type diets are fed i n which ZnS04 and either sodium phytate or This chapter not subject to U.S. copyright Published 1983 American Chemical Society Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
N U T R I T I O N A L BIOAVAILABILITY OF
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160
ZINC
soy p r o t e i n are the d i e t a r y source of z i n c and p h y t i c a c i d , r e s p e c t i v e l y (8,9,10). 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 to a s c e r t a i n the i n f l u e n c e of the d i e t a r y molar r a t i o of phytate/ z i n c on z i n c n u t r i t i o n o f humans. D i e t a r y f i b e r from wheat bran i n the d i e t of r a t s does not seem to i n f l u e n c e b i o a v a i l a b i l i t y of z i n c but the phytate does (JL1,12,JL3). D i f f e r e n t i a t i o n between the e f f e c t o f phytate and f i b e r i s d i f f i c u l t i n b i o a v a i l a b i l i t y s t u d i e s w i t h wheat bran or other c e r e a l and legume products t h a t c o n t a i n both phytate and d i e t a r y f i b e r . By the a c t i o n of the endogenous phytase, wheat bran can be dephytinized without changing the d i e t a r y f i b e r c o n c e n t r a t i o n (1^)· Although there may be an as yet u n i d e n t i f i e d chemical change i n the d i e t a r y f i b e r , e n z y m a t i c a l l y dephytinized wheat bran provides a r e l a t i v e l y high f i b e r food product from c e r e a l g r a i n that i s low i n phytate. We conducted a human metabolic balance study to t e s t the concept o f d i e t a r y p h y t a t e / z i n c molar r a t i o as a p r e d i c t o r o f z i n c b i o a v a i l a b i l i t y to humans. Using unaltered or e n z y m a t i c a l l y d e p h y t i n i z e d wheat bran w i t h o r d i n a r y foods we a t t a i n e d phytate z i n c molar r a t i o s of about 1 and 12 w i t h r e l a t i v e l y high i n t a k e s o f d i e t a r y f i b e r i n the menus and found no d i f f e r e n c e i n z i n c balance. R e t r o s p e c t i v e l y , the r e s u l t may be q u a l i f i e d on the b a s i s o f the magnitude of the z i n c i n t a k e and p o s s i b l e adaptive or homestatic responses over the period of the study. A second study was then conducted and a wider range o f p h y t a t e / z i n c molar r a t i o was provided than i n the f i r s t study. We w i l l b r i e f l y o u t l i n e the f i r s t study, g i v e a progress report on the second study and, w i t h some i n f o r m a t i o n on phytate i n t a k e s obtained by our l a b o r a t o r y , d i s c u s s the n u t r i t i o n a l i m p l i c a t i o n . Balance Study I Study P r o t o c o l and M a t e r i a l s . Ten healthy men ranging i n age from 23 to 48 years volunteered as subjects f o r the study. Each gave informed consent and was given a p h y s i c a l examination p r i o r to the study. An o u t l i n e o f the study p r o t o c o l i s shown i n Figure 1. Each phytate/zinc molar r a t i o was consumed f o r 15 days, three repeats o f the 5-day menu c y c l e . S t o o l and u r i n e c o l l e c t i o n s were pooled f o r the periods as i n d i c a t e d i n Figure 1. A f a s t i n g blood sample f o r serum z i n c a n a l y s i s was taken on days 1, 16 and 31. The menus c o n s i s t e d of foods r o u t i n e l y consumed i n the United S t a t e s . An example o f one day's menu i s given i n Table I . D i f f e r e n t c a l o r i c i n t a k e s were provided, to maintain each subjects weight, by v a r y i n g the amount of the non-muffin items i n i n c r e ments of 10% using the 3200 k c a l meals as base. Each subject consumed two bran muffins w i t h each meal, 6 g o f bran per m u f f i n . A l l food was supplied and cooked by the Human Study F a c i l i t y o f the B e l t s v i l l e Human N u t r i t i o n Research Center. Monday through F r i d a y meals were consumed at the Human Study F a c i l i t y and take-home packs were s u p p l i e d f o r weekends and one h o l i d a y .
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
11.
AND
MORRIS
15
Phytate/Zinc Molar Ratio
ELLIS
DAYS
15
161
DAYS
GROUP A WHOLE BRAN
MUFFINS
DEPHYTINIZED
GROUP
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DEPHYTINIZED
BRAN
I
WHOLE BRAN COLLECTION
II
STOOL
5,6
STOOL &
MUFFINS
PERIODS
III URINE
15
16
MUFFINS
Β
MUFFINS EXCRETA
1
BRAN
IV
STOOL
20,21
STOOL & URINE
31
Figure 1. Outline of experimental protocol. Menus repeated in 5-day cycles. T bran muffins consumed with each meal (6 g of bran/muffin). Five subjects e subgroup, A & B. Brilliant blue dye (50 mg) was given with breakfast on days 1, 6, 16, 21, and 31 (lower line) to aid in demarcation of stool.
DEIONIZED
WATER,
DRINKING,
B U T NO OTHER B E V E R A G E S WERE A L L O W E D .
THE TORY, OUR
INSTANT
WHEAT BRAN
WAS
LABORATORY AT B E L T S V I L L E ,
ONE-HALF OF
T H E BRAN
USED
DEIONIZED WITH
(WHOLE
PHYTASE WATER
CONSTANT
INCUBATION
(1
BRAN)
ACTIVITY G BRAN
SHAKING
THE ENTIRE
PRODUCTS,
STORED
AND
CONSUMED
6
CONSUMED
EACH
BUT 5
MUFFINS
(GROUP
CONSUMED ALTERNATE
DRIED BEFORE
G O F BRAN
OR 36
CONSUMED
COMPOSITES
SAMPLING
FOR
MUFFIN
A PORCELAIN CRUCIBLE
MUFFINS
AND
A
HOMOGENIZED AND
ML A L I Q U O T
DRY A S H E D .
ZINC
BRAN
WAS
WERE
SUBJECT
SUBJECT OF
THE
(GROUP 15
STUDY, B)
DAYS
AND T H E
DAYS.
FREEZE-DRIED 50
5
THE 3200 KCAL
SEPARATELY), WERE
EACH AND
37°
HYDROLYSIS
EACH
THE F I R S T 15
AT
T H E BRANS AND
BY IN
AFTER
AND
DAY.
T H E SECOND
WERE MADE O F
STOOLS
SUSPENDED
INCUBATED
USE.
IN
REFRIGER
OF DEPHYTINIZED
MUFFIN,
FOR
WAS
HOURS.
NUTRIENTS
EACH
MUFFINS
ANALYSIS.
AND 16
LABORA
WHEAT.
DEPHYTINIZED
WAS
OVER T H E COURSE
WHOLE BRAN
MUFFIN
COMPOSITED
FOR A N A L Y S I S .
PER
G O F BRAN
BRAN
T Y P E O F BRAN WERE
OR ABOUT
REFRIGERATED UNTIL 6
DEPHYTINIZED
DAILY (MUFFINS
ML WATER)
THE MINERAL
T Y P E O F BRAN A)
10
T H E BRAN
WATER S U S P E N S I O N
RETAINING
INTO MUFFINS,
TO
SPRING
O N E - H A L F WAS
(12).
OVERNIGHT
FREEZE-DRIED, BAKED
AND
FOR
T H E USDA WHEAT Q U A L I T Y RED
ENDOGENOUS
IN
M I L L E D BY
L O T O F HARD
UNTIL
ND
C O F F E E WERE S U P P L I E D
FROM A S I N G L E
ATED
FARGO,
T E A AND
MENU AND
ITEMS FREEZE-
THROUGHLY M I X E D
OF URINE
ANALYSIS
WAS
WAS
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
BY
DRIED FLAME
162
N U T R I T I O N A L BIOAVAILABILITY OF
Table I .
Example of One Day's Menu
ZINC
1
BREAKFAST Orange/Grapefruit Scrambled Egg Margarine Sausage L i n k s M i l k , 2% Muffins
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2
Jelly Margarine Sugar
2
2
Juice
124 grams 50 5 42 246 120 66 40 10
LUNCH Turkey Roast Macaroni Mayonnaise Cranberry J u i c e Ice Cream Muffins
90 70 15 126 100 120
DINNER Steak B o i l e d Potato Stewed Tomato Pumpkin P i e M i l k , 2% Grape J u i c e Muffins
2
10 50 50 100 2H6 253 120
I32OO 2
k c a l , 132 g p r o t e i n , 40% c a l o r i e s from f a t , P/S G i v e n with breakfast and used throughout the day.
0.66.
atomic absorption spectroscopy o f 1 N HC1 s o l u t i o n o f dry ashed d i e t or s t o o l composite. Phytate a n a l y s i s was by the method of E l l i s et a l . (14). N e u t r a l detergent f i b e r was determined by the approved method o f the American A s s o c i a t i o n of C e r e a l Chemists (15). Results Results p e r t a i n i n g to z i n c w i l l be summarized here. Information concerning other mineral n u t r i e n t s have been published i n part i n a b s t r a c t s and a short communication (16,17,18).
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
11.
MORRIS
NUTRIENT ZINC
INTAKE.
AND P H Y T I C
THE D I F F E R E N T ZINC
Phytate/ Zinc Molar Ratio
A N D ELLIS
SUMMARIZES
T H E RANGE O F Z I N C
C A L O R I C L E V E L S CONSUMED.
CONSUMED WAS CONTAINED
PHYTIC
A C I D WAS D E R I V E D
THE DAILY INTAKE
FROM T H E M U F F I N S
AND, SINCE
WAS NO D I F F E R E N C E
DUE TO T H E C A L O R I C L E V E L
BY AND
TABLE
II.
I N PHYTIC
I N PHYTIC
DAILY
INTAKES
MUFFIN
THERE
ACID
ACID
INTAKES.
INTAKES
T H E MEAN C A L C U L A T E D MOLAR R A T I O O F
WAS ABOUT 12 WHEN WHOLE BRAN M U F F I N S
G R E A T E R THAN 1 WHEN D E P H Y T I N I Z E D
JUST
T H E SAME
REGARDLESS O F CALORIC L E V E L ,
A TEN-FOLD DIFFERENCE
T Y P E O F BRAN M U F F I N .
OF THE
ABOUT 9 5 Î O F T H E
WAS E A T E N
PHYTATE/ZINC
INTAKES OF
I S T H E RESULT O F
ABOUT ONE-THIRD
IN THE MUFFINS.
NUMBER O F M U F F I N S
T H E R E WAS, HOWEVER,
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TABLE I I
ACID.
163
OF ZINC
AND P H Y T I C
ZINC
PHYTIC
WERE CONSUMED
BRAN M U F F I N S
WERE
ACID
P H Y / Z N MOLAR
ACID
RATIO
TYPE MG WHOLE BRAN
G
DEPHYTINIZED
-
18.9)
(10.5
1
-
13.6)
1
1.2
0.2
17.1
BRAN
11.8
2.0
16.8 (14.7
^-RANGE CONSUMED. SUPPLIED
A N EQUAL AMOUNT O F N E U T R A L D E T E R G E N T F I B E R WAS BY EACH
T Y P E O F BRAN M U F F I N .
G O F NEUTRAL DETERGENT F I B E R ZINC EACH
BALANCE.
15 DAY PERIOD
FIGURE
2.
T H E ZINC
AND I V , F I G U R E
WERE I N P O S I T I V E Z I N C
O F T H E T Y P E O F BRAN M U F F I N CONSUMED. SUBJECTS,
THE ZINC
WHOLE BRAN M U F F I N S .
INDIVIDUAL
ONE I N E A C H
B A L A N C E WHEN CONSUMING
O V E R A L L T H E MEAN B A L A N C E WAS 0 . 7
BRAN M U F F I N S .
10 DAYS O F A R E SHOWN I N
BALANCE REGARDLESS
O F T H E 10
ONLY TWO I N D I V I D U A L S ,
G R E A T E R WHEN E A T I N G WHOLE BRAN M U F F I N S IZED
1)
B A L A N C E FOR 8 WAS G R E A T E S T WHEN CONSUMING T H E
WERE I N MORE P O S I T I V E Z I N C BRAN M U F F I N S .
A MEAN O F 1 6
DAILY.
B A L A N C E S FOR T H E L A S T
(PERIODS I I
A L L SUBJECTS
BY ANALYSIS,
WAS CONSUMED
THIS
SUBGROUP,
DEPHYTINIZED
MG P E R DAY
THAN WHEN E A T I N G
DEPHYTIN-
D I F F E R E N C E WAS NOT S T A T I S T I C A L L Y
SIGNIFICANT. VALUES IN
FOR I N T A K E M I N U S F E C A L
TABLE I I I .
AND
III
AND T H E 10 DAYS
SEQUENCE FOR DAYS
EXCRETION OF ZINC
T H E V A L U E S AR E M G / D A Y FOR T H E 5 DAYS O F PERIODS
II
AND I V .
ARE P R E S E N T E D O F PERIODS
REGARDLESS
I N WHICH T H E TWO T Y P E S O F BRAN WERE CONSUMED,
VALUES
I N T A K E MINUS F E C A L E X R E T I O N WERE G R E A T E R FOR T H E L A S T EACH
TYPE O F MUFFIN
WAS CONSUMED
I
OF THE
THAN FOR T H E F I R S T 5
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
10 DAYS,
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164
NUTRITIONAL
SUBJECTS I
SUJECTS 6-10
BIOAVAILABILITY
OF
ZINC
A L L SUBJECTS
Figure 2. Zinc balances for metabolic periods II and IV. Mean daily balance for individual subjects shown in the sequence of type of bran muffin consumed. Wit each subgroup, each individual is represented by a different shapedfigure.Mean are shown by horizontal lines for each subgroup and the arrows for all subjects. Key: solid symbols, whole bran; and open symbols, dephytinized bran.
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
11.
PERIODS
II
AND I V COMPARED TO I
AND I I I ,
MAGNITUDE O F T H E S . D . FOR P E R I O D S INDIVIDUALS
O F EACH
THAN WAS CONSUMED,
SUBGROUP
FECAL
E X C R E T I O N V A L U E S WERE ALWAYS
FIRST
5 DAYS
TABLE
MUFFINS
DEPHYTINIZED
BRAN
LESS
PERIOD
THE
I N MAGNITUDE
MINUS
THAN T H E
WERE CONSUMED,
GROUP A
III VS. I.
EXCRETION OF ZINC
I
II
PERIOD
2
III
MG/DAY
IV
1
(zl
(+)3 -1.4+1.8
I.
THE INTAKE
EXCRETA COLLECTION
SUBGROUP
THAT SOME
I N T H E STOOL
A DURING
CONSUMED
MUFFINS
I N T A K E MINUS F E C A L
SUBJECT
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WERE
V S . I L L AND Β P E R I O D S
III.
RESPECTIVELY. THE
AND I I I V E R I F Y
E S P E C I A L L Y SUBGROUP
5 DAYS WHOLE BRAN
I
I
E X C R E T E D MORE Z I N C
FIRST
PERIODS
165
Phytate IZinc Molar Ratio
MORRIS A N D ELLIS
3.2+0.9
1.8+3.6
2.4+1.6
0.9+2.0
(-)
2.4+1.1 (+)
1.2+1.3
3.0+0.4
IMEAN + S . D . 2
SEE
FIGURE
3(+)
1.
WHOLE BRAN SERUM Z I N C
SERUM Z I N C DURING 1
RESPONSE.
DEPHYTINIZED
TABLE
THE STUDY.
THE INITIAL DURING
OF PHYTATE. PHYTATE
OBERLEAS DISCUSSES
THAT I N F L U E N C E RATS
GROWTH,
EQUIVALENT
TO WHEN Z N S 0 4
APPARENTLY
THEZINC
OF ZINC
ZINC
RATS
EXHIBIT
ZINC
(9,20).
ABSORPTION,
ZINC
ZINC OF ANY
R E S P O N S E WAS
SOURCE. COMPLEXES D I S S O C I
FROM E X T R A C T I N G T H E Z I N C .
I N THE DIET SIGNS
I N 12
TO 1 5 - F O L D
T H E M E T A B O L I C B A L A N C E DOES
OF B I O A V A I L A B L E NUTRIENT
HOWEVER,
WHEN
MOLAR E X C E S S
OVER
O F DECREASED B I O A V A I L A B I L I T Y NOT MEASURE
B U T A MEASURE C A N B E O B T A I N E D
BIOAVAILABILITY
SOME O F
T R A C T OR T H E COMPLEX I S NOT STRONG ENOUGH
TO P R E V E N T T H E I N T E S T I N E IS PRESENT
B U T NOT FEMUR Z I N C
WAS T H E D I E T A R Y
FOR 1 5
I N THE PRESENCE
O F WATER I N S O L U B L E
O F T H E S E WATER I N S O L U B L E
IN THE DIGESTIVE
PHYTATE
BRAN
DIFFERENT.
OR C A L C I U M - Z I N C P H Y T A T E C O M P L E X E S I N T H E A B S E N C E
ADDED P H Y T A T E ( . 1 0 , 1 9 ) .
ATES
T H E MEAN S E R U M Z I N C WAS
I N THESE PROCEEDINGS
THEZINC
TYPE OF
VALUES
Β WAS LOWER THAN
THE DEPHYTINIZED
THE SOLUBILITY
CAN U T I L I Z E
EACH
SERUM Z I N C
WERE S T A T I S T I C A L L Y
B U T T H E MEANS WERE NOT S I G N I F I C A N T L Y
FACTORS
CONSUMING
MEAN FOR SUBGROUP
T H E STUDY
A V E R A G I N G BOTH S U B G R O U P S ,
DISCUSSION. THE
MUFFINS.
I V I S A SUMMARY O F T H E I N I T I A L
iJg/100 ML G R E A T E R A F T E R CONSUMING
DAYS,
BRAN
T H E TENDENCY WAS TOWARD H I G H E R
AND T H E I N C R E A S E S
SIGNIFICANT. 10
(-)
V A L U E S AND A T T H E END O F 1 5 DAYS
BRAN M U F F I N S . A S
MUFFINS,
UNDER
A GIVEN
WOULD B E I N D I C A T E D
O F DIETARY TRUE
OVER T I M E O F T H E AMOUNT
DIETARY
REGIMEN.
DECREASED
BY A DECREASE I N APPARENT
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
166
NUTRITIONAL
BIOAVAILABILITY
OF
ZINC
Table IV. Serum Zinc Response to Bran Muffins
Sub jec t Subgroup
Day 16
Day 1
Day
31
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Pg/100 ml A
92+23
Β
80+ll
a
(+)2ll7+l6
(-)111+12
(-)
(+)110+13°
136+8°
iMean + S.D., F a s t i n g blood sample morning o f day i n d i c a t e d . (+)Whole bran muffins preceding 15 days, (-) dephytinized bran muffins preceeding 15 days. a,b,c S i g n i f i c a n t l y d i f f e r e n t , Ρ < 0.05. 2
a b s o r p t i o n , that i s an i n c r e a s e i n f e c a l e x c r e t i o n r e l a t i v e to i n t a k e . Apparent absorption o f z i n c by subjects on our study was lower the f i r s t 5 days the whole bran muffins were consumed than when dephytinized bran muffins were consumed, mean -0.2 and 1.5 mg/day, r e s p e c t i v e l y . T h i s i n d i c a t e s that the 12 molar r a t i o o f phytate/zinc decreased b i o a v a i l a b i l i t y o f z i n c the i n i t i a l 5 days whole bran muffins were consumed and e v i d e n t l y prevented r e a b s o r p t i o n o f z i n c that had been secreted i n t o the i n t e s t i n e (some i n d i v i d u a l s excreted more i n the s t o o l than they consumed). However, the r e l a t i o n reversed over the remaining 10 days each regimen was eaten, 3.1 v s . 2.4 mg/day f o r whole bran and dephytin i z e d bran muffins, r e s p e c t i v e l y . Reversal o f the apparent absorption values suggest an adaptation to the d i e t , e i t h e r a change i n the a b i l i t y o f the i n t e s t i n e to absorb z i n c or a homeostatic response which decreases s e c r e t i o n o f endogenous z i n c i n t o the i n t e s t i n e . The i n t a k e o f z i n c i n our study was g r e a t e r than from some h o s p i t a l and s e l f chosen d i e t s (20,21,22) and exceeded s l i g h t l y the recommended d i e t a r y i n t a k e (3). We d i d not determine the usual i n t a k e by our v o l u n t e e r s p r i o r to the study and i t i s p o s s i b l e t h a t the magnitude o f the balances was i n f l u e n c e d by the high i n t a k e s . The f a s t i n g serum z i n c values during the study were markedly elevated compared to the i n i t i a l value, supporting the conjecture that they consumed more z i n c during than p r i o r t o the study. Prasad summarizes l i t e r a t u r e i n d i c a t i n g that balance may i n c r e a s e during a p e r i o d o f adequate z i n c i n t a k e when preceded by a period o f low i n t a k e (23). Women showed increased plasma response to a z i n c load f o l l o w i n g a v e g e t a r i a n d i e t compared to a f t e r a d i e t that contained meat (24). The dephytinized bran contained the same percentage o f n e u t r a l detergent f i b e r as the nonincubated whole bran. Thus, the i n t a k e s o f n e u t r a l detergent f i b e r d i d not d i f f e r between the two d i e t a r y
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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11.
MORRIS
A N D ELLIS
Phytate I Zinc Molar Ratio
167
regimens. Experiments on i r o n absorption by humans i n d i c a t e the d e p h y t i n i z a t i o n process may a l t e r b i n d i n g o f i r o n by d i e t a r y f i b e r i n wheat bran (25). Lower z i n c balances when dephytinized wheat bran was consumed might i n d i c a t e the a f f i n i t y f o r z i n c by the f i b e r i n dephytinized bran may be g r e a t e r than t h a t of the f i b e r i n the unincubated whole bran. That c o n c l u s i o n i s e q u i v o c a l , however, i f based only on our study. The molar r a t i o o f p h y t a t e / z i n c o f some mid-eastern d i e t s was estimated to be 20 (26), but only small amounts of meat were g e n e r a l l y a v a i l a b l e . Sandstrom et a l . obtained r e s u l t s t h a t i n d i c a t e absorption of z i n c from a meal may be a p p r e c i a b l y i n f l u e n c e d by the type o f p r o t e i n i n the meal (27,28). Our menus provided p r o t e i n from meat i n most of the meals which may have a f f e c t e d b i o u t i l i z a t i o n o f the d i e t a r y z i n c . I n one comparison Sandstrom et a l . found t h a t whole wheat bread decreased percentage a b s o r p t i o n , but the absolute amount o f z i n c absorbed was g r e a t e r because t o t a l z i n c i n the whole wheat bread meal was g r e a t e r . Although the balance r e s u l t s i n d i c a t e that i n human d i e t s a phytate/zinc molar r a t i o o f 12 i s not a d e t e r r e n t to adequate z i n c n u t r i t u r e i n a d u l t men, q u a l i f i c a t i o n s as discussed above r a i s e questions i n i n t e r p r e t i n g the p r a c t i c a l a p p l i c a t i o n . We have pursued two questions (1) What i s the molar r a t i o o f phytate/ z i n c i n our t y p i c a l d i e t s ? (2) What would be the e f f e c t o f lower z i n c i n t a k e s i n a metabolic balance study with phytate/zinc molar r a t i o as the v a r i a b l e ? Part o f question 1 has been completed, but only p r e l i m i n a r y i n f o r m a t i o n i s a v a i l a b l e on question 2. A n a l y s i s of H o s p i t a l and Self-Chosen
Diets
Sample t r a y s o f three d i f f e r e n t h o s p i t a l menus, r e g u l a r , ovo-lacto vegetarian and soy-meat s u b s t i t u t e , were c o l l e c t e d f o r seven c o n s e c t i v e days and analyzed f o r minerals, p h y t i c a c i d and f i b e r (29). Each meal was composited, homogenized and analyzed s e p a r a t e l y . The c a l c u l a t e d c a l o r i c l e v e l o f the meals was 2800 k c a l per day. The mean d a i l y amount o f z i n c , phytate, f i b e r and the molar r a t i o phytate/zinc provided by the three d i e t s i s summarized i n Table V. Only the soy-meat s u b s t i t u t e d i e t supplied the recommended d i e t a r y i n t a k e o f z i n c f o r a d u l t males. The values found f o r the r e g u l a r and ovo-lacto vegetarian menus are s i m i l a r to those reported by Brown et a l . (20). The p h y t i c a c i d i n the ovo-lacto vegetarian menu was s l i g h t l y g r e a t e r than i n the r e g u l a r menu, but both were c o n s i d e r a b l y l e s s than provided by the soy-meat s u b s t i t u t e menu. The phytate/zinc molar r a t i o o f soy-meat s u b s t i t u t e menu was about 2.3 and 1.7 times g r e a t e r than o f the r e g u l a r and ovo-lacto vegetarian menus. The r a t i o of 7.6 i s , however, considerably lower than 12 from our human study I . N e u t r a l detergent f i b e r content o f the r e g u l a r and ovo-lacto v e g e t a r i a n d i e t s was s i g n i f i c a n t l y l e s s than i n the soy-meat s u b s t i t u t e and the l a t t e r d i e t supplied an amount equal
Inglett; Nutritional Bioavailability of Zinc ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
168
NUTRITIONAL
TABLE
V.
ANALYSIS THREE
OF ZINC,
HOSPITAL
NUTRIENT
ACID
(26)
REGULAR
ZINC MG/DAY
PHYTIC
PHYTIC
DIETS
ACID
12.2
+
3.3
387
+
60
3.3
+
1.4
7.8
+
0.6
a
AND F I B E R
S U P P L I E D BY
1
OVO-LAETO
SOY-MEAT
V E G E TARIAN
S UB ST I TU T E
A
9.7
+ 1.4
440
+ 210
A
4.5
+ 0.8
A
9.4
+
A
BIOAVAILABILITY O F ZINC
15.0
+
1.8°
1144
+
I44
B
B
7.6
+
0.7
C
A
16.9
±
1.7
B
A
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MG/DAY
PHY/ZN
2
FIBER3
3.3
G/DAY
^MEAN + S D FOR 7 DIFFERENT MULTIPLE 2
MOLAR
CONSECUTIVE
SUPERSCRIPT RANGE T E S T ,
RATIO
3NEUTRAL
Ρ
DETERGENT
THE OVO-LACTO VEGETARIAN
STUDY
DIET.
T H ESLIGHT OVER
CONTAINED
ZINC
BRIEF
BELOW,
AND BROUGHT ALL
FOOD
JUICES,
15
AND L I Q U I D AND L I Q U I D S IS
ADDITIONAL
ZINC,
ZINC
FROM 5 . 6 2.1
RANGED ZINC
TO 2 0 . 6 MG.
FROM 3 0 0
FROM 3 . 5
DIETS
WITH
OVERALL
FOOD,
WERE K E P T
ADDED
(SD O F + MG/DAY.
3.9)
DESCRIBED
FOR 1 W E E K ,
INCLUDING
DIET
ZINC
WILL
O F T H E FOOD
CONTRIBUTE
TO 2 5 0 0
CONTENT O F T H E FOOD
INDIVIDUAL MG/DAY ONLY
MEAN P H Y T A T E / Z I N C
ACID
MOLAR R A T I O
RANGED
FROM
OF PHYTATE/
INDIVIDUALS
G R E A T E R THAN WAS 7 . 2
AND S E L F - C H O S E N
RANGED
FOR I N D I V I D U A L S
AND T H E MOLAR R A T I O
TWO O F T H E 15
OF PHYTATE/ZINC
OF HOSPITAL
INTAKES
INTAKES
LITTLE
OF THE COMPOSITES
FOR I N D I V I D U A L S
DAILY
DIARIES
DUPLICATING
M I L K AND F R U I T
ANALYSIS
LIQUIDS
AND MEANS
T H E MEAN P H Y T I C
ZINC
FOR T H E M E A T , AND
T H E R E F O R E WE KNOW A C L O S E A P P R O X I M A T I O N
TO 1 6 . 4 .
OUR A N A L Y S I S
WERE
FOR T H E LOW
BALANCE STUDY,
SEPARATE.
T H E BULK
THAT
THAN T H E
LOW.
MAINTAINED
CONSUMED.
MEAN MOLAR R A T I O
INFORMATION
SUBSTITUTED
I N A SECOND
T H E MEAN D A I L Y
MG/DAY
TO 2 9 . 2
PRODUCTS
TO COMPENSATE
MENU WAS
VOLUNTEERS
COMPLETED.
INTAKES. 11.2
MENU
INDICATES
ITEMS
TO T H E LABORATORY 2ND P L A T E C O L L E C T I O N S
COMPOSITES
WAS
BY T H I S
TO P A R T I C I P A T I N G
I N P H Y T A T E AND F I B E R
MORE WHOLE G R A I N
I N D A I R Y PRODUCTS
SUPPLIED
PRIOR
INCREASE
T H E REGULAR D I E T
B U T , NOT ENOUGH WHOLE G R A I N
THE OVO-LACTO VEGETARIAN
CONCENTRATION
IN
I.
FORMER P R O B A B L Y
THE
WITH
BY D U N C A N ' S
FIBER.
OUR HUMAN
TO
IN A LINE
DIFFERENT