Nutritional Bioavailability of Calcium - American Chemical Society

15 Effect of Dietary Fat and Fiber on Calcium Bioavailability CONSTANCE KIES

Downloaded by UNIV LAVAL on July 10, 2016 | http://pubs.acs.org Publication Date: April 2, 1985 | doi: 10.1021/bk-1985-0275.ch015

Department of Human Nutrition and Food Service Management, University of Nebraska, Lincoln, NE 68583 Among the many dietary factors which may influence the absorption of calcium from the intestines are kind and level of dietary fiber and kind and level of dietary fat. Over the last 40 years, considerable amounts of evidence have been gathered from epidemiological and controlled laboratory studies concerning interactions between dietary fiber intake and bioavailability of calcium. Apparently certain kinds of dietary fiber fed under certain conditions can have an adverse effect on the intestinal absorption of calcium. Whether or not a specific kind of dietary fiber has an effect on calcium absorption is dependent upon the chemical-physical properties of the particular fiber, food or diet in whichitis included, the level fed, and physiological characteristics of the individual eating it. The role of dietary fat as a factor influencing the intestinal absorption of calcium has been less extensively investigated. Fatty diarrhea in which the usual efficient fat absorption is deranged also has a pronounced adverse effect on the absorption of calcium. Under some conditions, calcium bioavailability appears to decrease as chain length of fatty acids increase and as the degree of unsaturation decreases. Results of studies designed to investigate effects of level of dietary fat on calcium absorption have given mixed results. H i g h i n c i d e n c e s o f a t h e r o s c l e r o s i s / c o r o n a r y h e a r t d i s e a s e and c a n c e r i n t h e U n i t e d S t a t e s have l e d t o programs e n c o u r a g i n g Ameri c a n s t o change t h e i r e a t i n g p a t t e r n s r e l a t i v e t o consumption o f d i e t a r y f i b e r and f a t (V). However, i n c r e a s e d i n t e r e s t i n p o s s i b l e d i e t a r y o r p h y s i o l o g i c a l f a c t o r s i n v o l v e d i n maintenance o f bone h e a l t h throughout l i f e has developed because o f t h e h i g h i n c i d e n c e of o s t e o p o r o s i s among e l d e r l y Americans ( 2 , 3 ) . The r o l e o f c a l c i u m b i o a v a i l a b i l i t y i n bone m i n e r a l h o m e o s t a s i s has n o t been f u l l y 0097 6156/ 85/0275 0175506.00/0 © 1985 American Chemical Society

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

176

N U T R I T I O N A L BIOAVAILABILITY O L C A L C I U M

defined. However, i t would appear advantageous t o d e f i n e a l l d i e t a r y c o n t r i b u t i o n s to calcium n u t r i t i o n a l s t a t u s . In p a r t i c u l a r , a l l consequences o f suggested d i e t a r y changes r e l a t i v e t o r e d u c i n g i n c i d e n c e o f one type o f p a t h o l o g i c a l c o n d i t i o n s h o u l d be i n v e s t i gated so t h a t a d d i t i o n a l , c o n c u r r e n t recommendations may be made i f found t o be d e s i r a b l e .


D i e t a r y F i b e r and C a l c i u m

Bioavailability

More than 40 y e a r s ago, c a l c i u m a b s o r p t i o n from brown (whole wheat) bread which was f e d t o human s u b j e c t s was found t o be p o o r e r than was t h a t when w h i t e ( e x t r a c t e d wheat f l o u r ) was f e d 04,5). Since then, many s t u d i e s have sought t o d e f i n e the e x t e n t o f i n h i b i t i o n of calcium i n t e s t i n a l b i o a v a i l a b i l i t y by v a r i o u s forms o f d i e t a r y f i b e r w i t h mixed r e s u l t s and c o n c l u s i o n s (6-18). Serum c a l c i u m l e v e l s were d e p r e s s e d w i t h the f e e d i n g o f 18 t o 100 g o f wheat b r a n t o human s u b j e c t s i n the study by Heaton and Pomare (10) but were u n a f f e c t e d by the f e e d i n g o f a p p r o x i m a t e l y 20 g o f wheat f i b e r i n t h e s t u d y by J e n k i n s e t a l . ( 1 9 ) . S i n c e b l o o d serum c a l c i u m l e v e l s tend t o be r e s i s t a n t t o change except under c o n d i t i o n s o f s e v e r e c a l c i u m d e f i c i e n c y , measurement o f b l o o d serum calcium l e v e l s i s probably not s u f f i c i e n t l y s e n s i t i v e to i n d i c a t e change i n c a l c i u m n u t r i t i o n a l s t a t u s i n s h o r t - t e r m f e e d i n g s t u d i e s . Most o f t h e forementioned s t u d i e s which examined the i n f l u e n c e o f v a r i o u s d i e t a r y f i b e r on t h e b i o a v a i l a b i l i t y o f c a l c i u m by human s u b j e c t s have depended upon the comparative measurements o f c a l c i u m c o n t e n t o f d i e t s and c a l c i u m c o n t e n t s o f s t o o l s and u r i n e . As reviewed by A l l e n ( 3 ) , c a l c i u m b a l a n c e s t u d i e s have d i s t i n c t l i m i t a t i o n s r e l a t i v e t o a c c u r a c y and p r e c i s i o n . However, t h e i r ease o f a p p l i c a t i o n and c o s t , l a b o r a t o r y equipment r e q u i r e m e n t s , and r e a l (or p e r c e i v e d ) s a f e t y i n comparison t o a v a i l a b l e r a d i o a c t i v e o r s t a b l e i s o t o p e methods c o n t i n u e t o make t h e i r use p o p u l a r . I n c a l c i u m b a l a n c e s t u d i e s , c a l c i u m a b s o r p t i o n i s assumed t o be t h e d i f f e r e n c e between c a l c i u m e x c r e t i o n i n t h e f e c e s and c a l c i u m intake. U s u a l l y t h i s i s e x p r e s s e d as a p e r c e n t o f the c a l c i u m intake. T h i s method assumes t h a t a l l f e c a l c a l c i u m l o s s i s unabsorbed d i e t a r y c a l c i u m which i s , o f c o u r s e , u n t r u e s i n c e a p p r e c i a b l e amounts o f c a l c i u m from the body a r e l o s t v i a the i n t e s t i n a l r o u t e through the b i l i a r y t r a c t . Hence, c a l c i u m a b s o r p t i o n by t h i s method may u n d e r e s t i m a t e a b s o r p t i o n o f d i e t a r y c a l c i u m but i s u s e f u l f o r comparative p u r p o s e s . I t has been e s t i m a t e d t h a t b i l e s a l t s may c o n t r i b u t e about 100 g c a l c i u m / d a y t o the i n t e s t i n a l calcium contents. B i l e s a l t c a l c i u m has been found t o be more e f f i c i e n t l y absorbed through the i n t e s t i n a l mucosa than i s d i e t a r y c a l c i u m (20) but l e s s so by o t h e r i n v e s t i g a t o r s ( 2 1 ) . Wheat b r a n has been t h e f i b e r s o u r c e most commonly used t o s t u d y e f f e c t s o f d i e t a r y f i b e r on c a l c i u m a b s o r p t i o n i n c o n t r o l l e d l a b o r a t o r y s t u d i e s . However, wheat b r a n and o t h e r forms o f f i b e r as they o c c u r i n food p r o d u c t s p r e s e n t s e v e r a l d i s a d v a n t a g e s i n terms o f d e f i n i t i o n and by c o n c u r r e n t l y a l t e r i n g i n t a k e s o f o t h e r s u b s t a n c e s o r m a t e r i a l s known o r s u s p e c t e d o f h a v i n g an adverse e f f e c t on the b i o a v a i l a b i l i t y o f c a l c i u m such as p h y t a t e s and o x a l a t e s (5,13,17,22-28). S e v e r a l s t u d i e s have been conducted which have sought t o s e p a r a t e o r compare t h e e f f e c t s o f p h y t a t e and f i b e r



15.

K IFS

Effect of Dietary Fat and

Fiber on Ca

Bioavailability

Ml

i n brans (29-31). R e s u l t s of McCance and Widdowson (29) i n d i c a t e d t h a t f e e d i n g d e p h y t a t e d whole wheat b r e a d r e s u l t e d i n improved c a l c i u m b i o a v a i l a b i l i t y ; however, c a l c i u m b i o a v a i l a b i l i t y remained i n f e r i o r to t h a t when w h i t e f l o u r bread was f e d . Reinhold et a l . (31) found t h a t f e e d i n g p u r i f i e d p h y t a t e had l i t t l e e f f e c t on calcium b i o a v a i l a b i l i t y but t h a t p h y t a t e - r i c h whole wheat b r e a d had a p r o nounced n e g a t i v e e f f e c t . S i n c e c a l c i u m i s thought to p o s s i b l y be a b s o r b a b l e i n the lower i n t e s t i n e , i t may be t h a t p h y t a t e i s d i g e s t e d s u f f i c i e n t l y e a r l y to a l l o w f o r the r e l e a s e of c a l c i u m and i t s subsequent a b s o r p t i o n but t h a t f i b e r i n h i b i t s the d i g e s t i o n o f p h y t a t e i t s e l f thus p r e v e n t i n g the r e l e a s e of c a l c i u m . Fecal p h y t a t e e x c r e t i o n i t s e l f has been found to be i n c r e a s e d w i t h f e e d i n g o f f i b e r - r i c h d i e t s i n comparison to f i b e r - p o o r d i e t s ( 3 2 ) . Thus, i t may be t h a t the c o m b i n a t i o n of h i g h p h y t a t e and h i g h f i b e r d i e t s i s more d e t r i m e n t a l to c a l c i u m a b s o r p t i o n than i s e i t h e r c a l c i u m a b s o r p t i o n i n h i b i t o r by i t s e l f . The term e d i b l e or d i e t a r y f i b e r i n c l u d e s a l a r g e v a r i e t y of m a t e r i a l s w i t h w i d e l y d i f f e r e n t p h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s (33-36). The o n l y common c h a r a c t e r i s t i c o f t h e s e s u b s t a n c e s marking them as f i b e r i s a r e s i s t a n c e to d i g e s t i o n i n the upper gastrointestinal tract. B i o l o g i c a l l y , p l a n t f i b e r s may be c l a s s i f i e d as a) s t r u c t u r a l components o f c e l l w a l l s ( c e l l u l o s e , l i g n i n , p e c t i n s and many h e m i c e l l u l o s e s ) ; b) gums and m u c i l a g e s ; and c) i n d i g e s t i b l e s t o r a g e p o l y s a c c h a r i d e s such as guar gum. A n a l y t i c a l l y , t h e s e f i b e r s can be c l a s s i f i e d as water s o l u b l e f i b e r s ( p e c t i n , some h e m i c e l l u l o s e s , m u c i l a g e s , a l g a l p o l y s a c c h a r i d e s and s t o r a g e p o l y s a c c h a r i d e s ) and water i n s o l u b l e f i b e r s ( c e l l u l o s e , some h e m i c e l l u l o s e s and l i g n i n ) . Not o n l y do t h e s e d i f f e r e n t d i e t a r y f i b e r s d i f f e r i n c h e m i c a l s t r u c t u r e and p h y s i c a l c h a r a c t e r i s t i c s i n v i t r o , but because of m o d i f i c a t i o n s due to e n v i r o n m e n t a l changes such as pH, d i g e s t i v e p r o c e s s , p r e s e n c e o f b a c t e r i a s and o s m o l a l i t y w i t h i n the g a s t r o i n t e s t i n a l t r a c t and a t d i f f e r e n t s i t e s w i t h i n the g a s t r o i n t e s t i n a l t r a c t , i n v i v o f u n c t i o n a l e f f e c t s f o r any f i b e r type may d i f f e r c o n s i d e r a b l y from p r e d i c t i o n s made on the b a s i s of i n v i t r o o b s e r v a t i o n s . Most food f i b e r s o u r c e s c o n t a i n m i x t u r e s o f f i b e r s u b s t a n c e s which makes a complex s i t u a t i o n even more c o n f u s i n g . In a d d i t i o n such p r e consumption treatment o f d i e t a r y f i b e r s o u r c e s such as degree o f p u r i f i c a t i o n , g r i n d s i z e , food items i n which the t e s t f i b e r s a r e c o n t a i n e d , o t h e r food items c o n c u r r e n t l y consumed, and degree o f p r e h y d r a t i o n of the f i b e r c o n t e n t may a l l i n f l u e n c e p h y s i o l o g i c a l impact o f t e s t f i b e r consumption. The p h y s i o l o g i c a l c h a r a c t e r i s t i c s o f the i n d i v i d u a l consuming the f i b e r s o u r c e perhaps has the g r e a t e s t i n f l u e n c e on d e f i n i n g the apparent p h y s i o l o g i c a l r e s p o n s e s of feeding p a r t i c u l a r test f i b e r s . Thus, i t s h o u l d not be s u r p r i s i n g t h a t t h e r e i s some l a c k o f agreement among l a b o r a t o r i e s and even w i t h i n the same l a b o r a t o r y on degree and even on d i r e c t i o n o f p h y s i o l o g i c a l r e s p o n s e o f f e e d i n g s p e c i f i c t e s t f i b e r s o u r c e s to humans. In a s e r i e s of human s t u d i e s at the U n i v e r s i t y o f Nebraska, a t o t a l o f 285 human a d u l t s were fed s e v e r a l d i f f e r e n t f i b e r s o u r c e s d u r i n g e x p e r i m e n t a l p e r i o d s of 5 to 7 days each. Some s u b j e c t s r e c e i v e d more than one t e s t f i b e r t r e a t m e n t ; however, a l l s u b j e c t s r e c e i v e d at l e a s t one f i b e r s o u r c e as w e l l as r e c e i v i n g the cont r o l l e d b a s a l d i e t d u r i n g one p e r i o d which i n c l u d e d no added f i b e r



178

M T R I T I O N A L BIOAVAILABILITY O L Γ Λ Κ Ί Γ Μ

source. T e s t f i b e r s o u r c e s were f e d i n amounts to p r o v i d e about 20 g f i b e r / d a y and were f e d a t each o f the t h r e e d a i l y meals as p a r t o f a bread product o r mixed w i t h peanut b u t t e r . A l a b o r a t o r y con t r o l l e d measured d i e t composed o f o r d i n a r y foods was f e d each day d u r i n g a l l s t u d i e s . S u b j e c t s made complete c o l l e c t i o n s o f u r i n e and s t o o l s throughout a l l s t u d i e s . Feces were d i v i d e d i n t o p e r i o d l o t s through use o f f e c a l dye markers. A l l studies provided s i m i l a r amounts o f c a l c i u m . M i l k was t h e p r i m a r y c a l c i u m s o u r c e . S u b j e c t s were p r i m a r i l y young female a d u l t s , u n d e r g r a d u a t e and graduate s t u d e n t s a t the U n i v e r s i t y o f Nebraska. A l l were assumed to be i n good h e a l t h and r e c e i v e d m e d i c a l c l e a r a n c e f o r p a r t i c i p a t i o n p r i o r t o the s t a r t o f each s t u d y from the U n i v e r s i t y o f Nebraska D i v i s i o n o f Student H e a l t h S e r v i c e s . The p r o j e c t was approved by the U n i v e r s i t y o f Nebraska I n s t i t u t i o n a l Review Board I n v o l v i n g t h e P r o t e c t i o n o f Human S u b j e c t s . U r i n e , f e c e s and food were a n a l y z e d f o r c a l c i u m content by atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y . Data w e r e s u b j e c t e d t o s t a t i s t i c a l a n a l y s i s by a n a l y s i s o f v a r i a n c e and Duncan's M u l t i p l e Range T e s t . E f f e c t s o f t h e v a r i o u s t e s t f i b e r s i n t h i s p r o j e c t on f e c a l and u r i n e l o s s e s o f c a l c i u m and on c a l c i u m b a l a n c e s a r e g i v e n i n T a b l e I . Apparent c a l c i u m a b s o r p t i o n s and c a l c i u m b a l a n c e s under these c o n d i t i o n s were c a l c u l a t e d from t h i s d a t a and a r e a l s o g i v e n i n Table I. A d d i t i o n o f b r a n from h a r d r e d and s o f t w h i t e wheat b r a n , p s y l l i u m f i b e r , and c e l l u l o s e r e s u l t e d i n i n c r e a s e d l o s s e s o f c a l c i u m i n f e c e s i n comparison t o l o s s e s when no f i b e r supplements were used ( P < 0 . 0 5 ) . U r i n a r y c a l c i u m l o s s e s were n o t s i g n i f i c a n t l y a f f e c t e d ; however, c a l c i u m b a l a n c e s were lowered when these f o u r f i b e r s o u r c e s were added t o the l a b o r a t o r y c o n t r o l l e d d i e t (P < 0.05). The adverse e f f e c t s o f f e e d i n g the two wheat b r a n s and p s y l l i u m f i b e r were s u f f i c i e n t l y l a r g e t o r e s u l t i n mean n e g a t i v e c a l c i u m balances. C o n s i d e r i n g t h a t t h e s e were young, h e a l t h y , a c t i v e a d u l t s u b j e c t s who would n o r m a l l y be expected t o be i n d i s t i n c t p o s i t i v e n i t r o g e n b a l a n c e at t h i s l e v e l o f c a l c i u m i n t a k e , t h e n e g a t i v e b a l a n c e s were unexpected. Over an extended p e r i o d o f time, nega t i v e c a l c i u m b a l a n c e s c o u l d r e s u l t i n c o n s i d e r a b l e body c a l c i u m loss. E f f e c t s o f f e e d i n g the o t h e r t e s t f i b e r s o u r c e s , c o r n b r a n , r i c e b r a n , and p e c t i n were n o t o f s u f f i c i e n t magnitude and/or o f s u f f i c i e n t c o n s t a n c y among s u b j e c t s t o be found s t a t i s t i c a l l y s i g n i ficant . I n t h i s s t u d y g r e a t e r wet f e c a l w e i g h t s were produced when t h e c e l l u l o s e , wheat b r a n and p s y l l i u m f i b e r s were f e d . Corn and r i c e b r a n f e e d i n g produced e q u a l l y h i g h amounts o f d r y f e c a l r e s i d u e s w h i l e f e c a l d r y and wet w e i g h t s produced w i t h p e c t i n f e e d i n g were no g r e a t e r than those produced when t h e b a s a l d i e t w i t h o u t f i b e r s u p p l e m e n t a t i o n was f e d . These r e s u l t s suggest t h a t b u l k i n g c a p a c i t y may have an i m p o r t a n t b e a r i n g on whether o r not a s p e c i f i c test f i b e r adversely influences calcium absorption. W a t e r - h o l d i n g c a p a c i t y o f h e m i c e l l u l o s e s ( c o n t a i n e d i n wheat brans and p s y l l i u m f i b e r ) and c e l l u l o s e s may d e c r e a s e mouth t o rectum t r a n s i t time, i n c r e a s e f e c a l w e i g h t , and d e c r e a s e i n t r a l u m i n a l p r e s s u r e (36). These c h a r a c t e r i s t i c s might be expected t o i n t e r f e r e w i t h c a l c i u m a b s o r p t i o n d e c r e a s i n g time a l l o w e d f o r i n t e s t i n a l a b s o r p t i o n , by d i l u t i n g t h e c o n c e n t r a t i o n o f c a l c i u m and


15.

KIES

Effect of Dietary Fat and Fiber on Ca Bioavailability

179

Table I . C a l c i u m U t i l i z a t i o n by Humans from D i e t s V a r i e d i n F i b e r Content


Diet

Urine Ca mg/day

+

1450 1474

532 502

796 1032

+

1471

551

950

+

1480

549

799

+

1492

512

827

+

1450

580

899

+

1450

551

+

1450

543

1

Basal Basal rwb Basal wwb Basal cb Basal rb Basal pf Basal Ρ Basal c

Fecal Ca Loss % Dietary Ca mg/day

Ca Intake mg/day

% Apparent Ca Absorption

Ca Balance +122 -60

a

45.I 30.0

e

b

35.6

b

-30

54.0

a

46.0

e

+132

a

55.4

a

43.4

e

+153

a

b

62.0

b

38.0

b

752

a

51.9

a

48.1

873

b

60.2

b

39.8

a

54.9 70.0

c

bc

a

ab

64.4

a

C

a

C

-29

be

b

e

+147

a

b

+34

b

Note: Mean v a l u e s f o r 127 s u b j e c t s . V a l u e s w i t h d i f f e r e n t l e t t e r s u p e r s c r i p t s were s i g n i f i c a n t l y d i f f e r e n t from one another ( P < 0 . 0 5 ) . *The basal diet was a measured, laboratory controlled diet based on ordinary foods fed i n s u f f i c i e n t quantities to meet c a l o r i c requirements of the 127 subjects for weight maintenance and meeting or exceeding the National Research Council Daily Recommended N u t r i ent Intakes. Diet Codes:

rwb = red wheat bran; wwb = white wheat bran; cb = corn bran; rb = r i c e bran; pf = psyllium f i b e r ; ρ = pectin; c = cellulose

by setting up a physical barrier to calcium absorption throughout the g a s t r o i n t e s t i n a l t r a c t . Calcium as well as other nutrients may well become trapped within the matrix of fiber strands. The gel formation a b i l i t y of such water-soluble f i b e r s as pectins and mucilages as guar gum may influence g a s t r i c emptying and increase mouth to cecum t r a n s i t time. These substances form viscous gels based on cross-linkages i n the small i n t e s t i n e s ; thus, i n t e s t i n a l absorption with the feeding of these fibers might be expected to be decreased due to reducing rate of d i f f u s i o n of calcium toward the i n t e s t i n a l mucosa as a result of entrapment of calcium i n the g e l structure. Increase i n mouth to cecum t r a n s i t time, however, might be expected to result i n increase i n calcium absorption by allowing greater time for absorption to occur i n the small intestines. In addition, increased mouth to cecum t r a n s i t


NUTRITIONAL BIOAVAILABILITY OF CALCIUM


180

time has been found to decrease b i l e acid flux which might reduce feedback i n h i b i t i o n of b i l e acid synthesis (36). B i l e acids and s a l t s have been found to enhance the absorption of both calcium and vitamin D; hence, to increase calcium absorption both d i r e c t l y and i n d i r e c t l y (3,37). However, the a b i l i t y of some dietary fibers such as l i g n i n and pectin to absorb conjugated and deconjugated b i l e s a l t s onto their surfaces to be excreted i n the feces (a mechanism credited to the hypocholesterolemic effect of some dietary f i b e r s ) may result i n an o v e r a l l decrease i n calcium absorption from the g a s t r o i n t e s t i n a l tract (7,33,38-40). Several other properties of selected dietary fibers may influence the b i o a v a i l a b i l i t y of calcium d i r e c t l y or i n d i r e c t l y . Those fibers which have cation exchange c a p a b i l i t i e s such as acid polysaccharides due to free carboxyl groups on the sugar residues may bind minerals such as calcium (3,17,33,36). Loss of calcium binding protein as a result of mucosa injury caused by the feeding of some kinds of dietary f i b e r was credited as being the p a r t i a l cause of decreased calcium absorption i n everted, r a t gut sac studies by Oku et a l . (16). In the studies discussed, wheat bran, c e l l u l o s e , and psyllium f i b e r feeding resulted i n increased f e c a l fat losses and i n lowered blood serum cholesterol and t r i g l y c e r i d e levels (14,15,32,41) as well as increased fecal losses of calcium. Possible involvement of dietary fat with high or low dietary f i b e r intake has not been extensively investigated. However, that calcium i s involved i n i n t e s t i n a l fat absorption i s generally accepted (42-45). Dietary Fat and Calcium

Absorption

Interest i n the possible connection between intake of fat and absorption of calcium was generated by the concurrent massive losses of calcium i n patients with steatorrhea, f a t t y diarrhea (46, 47). O r d i n a r i l y , however, fat i s very e f f i c i e n t l y absorbed from the g a s t r o i n t e s t i n a l t r a c t . Results of several studies i n human adults and c h i l d r e n indicate l i t t l e or no effect of l e v e l of dietary fat on absorption of calcium (48-54). However, influence of l e v e l of dietary fat on calcium absorption i n rat studies has produced c o n f l i c t i n g results (55-57). In steatorrhea, the formation and p r e c i p i t a t i o n of insoluble calcium soaps formed from calcium and f a t t y acid has been generally credited as the cause of reduced calcium and fat absorption. However, Patton and Carey (42) have suggested that calcium soap formation i s a part of usual l i p i d digestion. Other research indicates that the a v a i l a b i l i t y of calcium from calcium soaps infused into rat i n t e s t i n e s increases as fatty acid chain length decreases ans as degree of polyunsaturatedness increases (58). Basu and Nath (59), studied calcium absorption i n young men eating diets varied i n levels of calcium. Diets were either nearly f a t free or contained fat supplied primarily by butterfat, sesame o i l , peanut o i l , coconut o i l or mustard seed o i l . Feeding of a l l test fats except coconut o i l resulted i n a s l i g h t decrease i n fecal calcium, thus, an assumed increase i n calcium b i o a v a i l a b i l i t y . However, feeding of coconut o i l (a highly saturated fat) resulted i n increased f e c a l and urinary losses of calcium.



15.

KIES

Effect of Dietary Fat and

Fiber on Ca

Bioavailability

181

Fat absorption has been found to be less e f f i c i e n t i n infants than i n adult humans (60-63). Thus, the p o t e n t i a l for formation and p r e c i p i t a t i o n of calcium soaps i n h i b i t i n g the absorption of calcium would appear to be greater. Furthermore, formulation of products to best promote both fat and calcium u t i l i z a t i o n by b o t t l e fed infants would appear to be a desirable, obtainable objective. Several studies have been conducted on calcium-fat interactions i n human infants (64-70). Low synthesis of b i l e s a l t s and low pancreatic lipase a c t i v i t y may be responsible for poorer fat u t i l i z a t i o n i n infants than i n adults (63,71). Fat from infant formulas may be lower than that from human milk because of the lack of a bile-stimulated l i p a s e i n the former (72). In infants, fat absorption tends to decrease with increase i n f a t t y acid length, with lower degree of saturation, and with increase of t o t a l fat (3). T r i g l y c e r i d e structure may also influence fat absorption i n the infant and, thus, i n d i r e c t l y , might also affect calcium absorption i n the infant. Fat and calcium from infant formulas high i n stéarate and palmitate have been found to be poorly u t i l i z e d (70). Fecal excret i o n of palmitate and stéarate and of calcium were correlated by Hanna et a l . (64). Both calcium and fat absorption i n infants and i n patients with b i l i a r y c i r r h o s i s and subtotal gastrectomies have been improved by dietary substitution of medium chain t r i g l y c e r i d e s for long chain t r i g l y c e r i d e s (47,68,72,73). Medium chain t r i g l y c e r i d e s are more soluble than are long chain t r i g l y c e r i d e s and do not require b i l e s a l t s for their digestion and absorption. Data have been collected from several studies completed at the University of Nebraska to further investigate calcium-fat or calcium-fat-fiber interactions possibly influencing calcium u t i l i z a t i o n . In one study, 15 adolescent boys were fed measured, laboratory-controlled diets based on ordinary foods containing 886 mg of calcium and 12 g of dietary f i b e r from mixed sources per day. Caloric intake was maintained at l e v e l s necessary for s l i g h t weight gain i n each subject. Dietary fat was maintained at 30% of the calories with the chief fat sourcesbeing safflower o i l , soybean o i l and apricot kernal o i l . These o i l s have saturated to monounsaturated to polysaturated r a t i o s of 7:11:80, 45:35:44 and 5:71:23, respectively. The 15 boys were divided into three groups of f i v e boys each. Each group was assigned one of the three test fat diets for 20 days. Data presented are based on the l a s t f i v e days. Other aspects of t h i s study r e l a t i v e to excreta processing and chemical and a n a l y t i c a l analyses were as described i n the e a r l i e r discussed study. Mean urine and f e c a l losses of calcium of subjects while receiving the three test fats are shown on Table I I . Apparent calcium absorptions and calcium balances were calculated from t h i s data. Mean f e c a l calcium losses when safflower o i l , soybean o i l and apricot kernal o i l were fed were 460, 500 and 520 mg/day. With a p r o b a b i l i t y of only Ρ < 0 . 1 0 , these difference were not s t a t i s t i c a l l y s i g n i f i c a n t although a strong trend toward increased f e c a l calcium losses with degree of saturatedness of the dietary fat was shown. Thus, a trend toward increase i n calcium absorption with more polyunsaturated fats was i l l u s t r a t e d . Coupled with changes i n


182

NUTRITIONAL BIOAVAILABILITY OF CALCIUM

urinary nitrogen these changes were s u f f i c i e n t l y large and consis tent to result i n changes i n calcium balance which were s i g n i f i c a n t l y d i f f e r e n t . These results thus somewhat support those of Gacs and Barltrop (58) that fatty acid chain length may influence b i o a v a i l a b i l i t y of calcium. Table I I . C a l c i u m U t i l i z a t i o n from Low Fat D i e t s V a r i e d i n Saturated:Monounsaturated:Polyunsaturated Fatty A c i d Ratios by A d o l e s c e n t Boys


Diet

Ca Intake mg/day

1

Fecal Ca Urine % Dietary Ca mg/day Ca mg/day

Safflower o i l 7:11:80

886

a

210

Soybean o i l 45:35:44

886

a

228

a

a

a

a

460

a

51.9

500

a

56.4

a

a

a

a

% Apparent Ca Absorption

Ca Balance

48.l

a

216

a

43.6

a

158

b

a

b

Apricot kernal 886 232 520 58.7 41.3 134 oil 5:71:23 Note: Mean v a l u e s f o r 15 s u b j e c t s , 5 s u b j e c t s per group. V a l u e s w i t h d i f f e r e n t l e t t e r s u p e r s c r i p t s were s i g n i f i c a n t l y d i f f e r e n t from one another ( P < 0 . 0 5 ) . l-The d i e t s were a measured, l a b o r a t o r y - c o n t r o l l e d d i e t based on o r d i n a r y foods. F a t s p r o v i d e d 307 o f t h e d i e t a r y c a l o r i e s . Satur a t e d t o monounsaturated t o p o l y u n s a t u r a t e d f a t t y a c i d r a t i o s a r e l i s t e d below each t e s t f a t . o

Effects of two levels of dietary fat on dietary calcium u t i l i z a t i o n were investigated i n another study conducted at the Univer s i t y of Nebraska. A group of 10 healthy, young adult subjects who were fed a measured, laboratory controlled diet based on ordinary foods providing 43% of the calories from mixed sources of fat were i n d i v i d u a l l y age, sex, race, and weight matched to subjects from other studies consuming measured, laboratory controlled diets providing approximately the same amount of calcium but only 23% of the calories from various fat sources. Other aspects of these studies were b a s i c a l l y as previously described. As shown i n Table I I I , mean f e c a l calcium losses tended to be higher when the higher fat diet was fed i n comparison to results when the lower fat diet was fed. Therefore, apparent calcium absorption was higher when the low fat diet was fed. These d i f f e r ences were s i g n i f i c a n t at only the Ρ

Nutritional Bioavailability of Calcium - American Chemical Society

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