9 Effect of Dietary Protein On Skeletal Integrity in Young Rats
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Faustina Bohannon and Gur Ranhotra Nutrition Research, American Institute of Baking, Manhattan, KS 66502
A number of nutrients affect bone integrity early in l i f e . While the role of certain minerals and vitamins bearing on skeletal integrity is well established, that of protein remains controversial, especially when consumed in excessive amounts. Protein-included calciuric effect as observed in adult man and animals may also occur early in l i f e and thus conceivably affect peak bone mass adversely, particularly when calcium intakes may be marginal. In studies reported here (test model: young female rats), i t was found that a diet approaching adequacy in protein and based equally on plant and animal sources would favor some parameters which bear on skeletal mass at maturity more than other combinations of protein consumed. S e v e r a l f a c t o r s , d i e t - r e l a t e d and o t h e r s , a f f e c t bone mass, and thus skeletal integrity early in l i f e . I t i s suspected that i n d i v i d u a l s w i t h l a r g e bone mass a c q u i r e d e a r l y i n l i f e (peak bone mass) a r e l e s s l i k e l y to d e v e l o p o s t e o p o r o s i s — t h i n n i n g o f b o n e s — i n l a t e r y e a r s than i n d i v i d u a l s w i t h l e s s e r bone mass ( 1 - 3 ) . W h i l e the d i e t a r y i n adequacy of c e r t a i n m i n e r a l s and v i t a m i n s t h a t a f f e c t s k e l e t a l mat u r i t y a d v e r s e l y i s w e l l documented, f o r p r o t e i n our c o n c e r n c e n t e r s around the e x c e s s i v e i n t a k e of t h i s n u t r i e n t . P r o t e i n - i n d u c e d c a l c i u r i c e f f e c t o b s e r v e d i n a d u l t man and a n i m a l s i s i m p l i c a t e d by some (4-6)as a c o n t r i b u t o r y f a c t o r i n the e t i o l o g y o f o s t e o p o r o s i s . P r o t e i n - i n d u c e d c a l c i u r i a , i f o c c u r r i n g e a r l y i n l i f e , may c o n t r i b u t e to an e a r l y onset of o s t e o p o r o s i s by a d v e r s e l y a f f e c t i n g the peak bone mass, e s p e c i a l l y when c a l c i u m i n t a k e may be m a r g i n a l . The s t u d i e s r e p o r t e d h e r e were u n d e r t a k e n to examine t h i s l a t t e r p o s s i b i l i t y under c o n d i t i o n s w h e r e i n the s o u r c e of d i e t a r y p r o t e i n a l s o varied. M a t e r i a l s and
Methods
Six p r o t e i n s o u r c e s — t w o p l a n t - d e r i v e d and f o u r a n i m a l - d e r i v e d — w e r e used i n t h i s 2 x 3 f a c t o r i a l type study ( T a b l e I ) . D i e t s were formu-
0097-6156/86/0312-0100S06.00/0 © 1986 American Chemical Society
Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
9.
BOHANNON AND RANHOTRA
Effects of Protein on Skeletal Integrity
101
l a t e d u s i n g t h r e e c o m b i n a t i o n s o f p r o t e i n s o u r c e s , t o c o n t a i n 10% o r 30% p r o t e i n . D i e t s were complete i n a l l n u t r i e n t s r e q u i r e d by t h e r a t (7) except c a l c i u m which was p r o v i d e d a t 60% o f t h e r e q u i r e m e n t level. C a l c i u m (O.3%), phosphorus (O.4%), magnesium, z i n c , sodium and p o t a s s i u m l e v e l s were a l l e q u a l i z e d between d i e t s . Additional i n f o r m a t i o n on d i e t s i s p r o v i d e d e l s e w h e r e ( 8 ) . Table
I.
Experimental
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D i e t No. Level (%)
Design
( 2 x 3 Factorial)
Dietary Protein Type (% o f T o t a l ) Plant Animal a
A Β C
10 10 10
67 50 33
33 50 67
D Ε F
30 30 30
67 50 33
33 50 67
b
a
A s bread: Bread was made w i t h w h i t e wheat f l o u r , wheat g l u t e n and d e f a t t e d soy f l o u r . ^Sources used: Cooked ground b e e f , parmesan c h e e s e , non f a t d r y m i l k and egg w h i t e powder. Weanling female r a t s were used as t h e t e s t model i n t h e s e studies. They were housed i n d i v i d u a l l y (10 r a t s / d i e t ) and o f f e r e d d i e t and d e i o n i z e d water ad l i b i t u m f o r 5 months. Apparent c a l c i u m and phosphorus a b s o r p t i o n and u r i n a r y Ca and Ρ l o s s e s were measured on c o l l e c t i o n s made the l a s t f i v e days each month. U r i n e volume and pH v a l u e s were a l s o r e c o r d e d . Other d a t a (growth r e s p o n s e , serum Ca and Ρ l e v e l s , femur m i n e r a l c o m p o s i t i o n , femur s t r e n g t h and d e n s i t y , and femur h i s t o l o g y ) were o b t a i n e d a t t h e end o f t h e 5-month f e e d i n g study. D e t a i l s o f t h i s and t h e a n a l y t i c a l methods used a r e p r e s e n t ed e l s e w h e r e ( 8 ) . A l l d a t a were s u b j e c t e d t o a p p r o p r i a t e s t a t i s t i c a l analyses. R e s u l t s and D i s c u s s i o n P h y s i o l o g i c a l Responses. The v a r i o u s p h y s i o l o g i c a l r e s p o n s e s mea s u r e d i n r a t s a t t h e end o f t h e 5-month f e e d i n g p e r i o d a r e summarized i n T a b l e I I . These r e s p o n s e s were o b t a i n e d on d i e t s which were com p l e t e i n a l l r e q u i r e d n u t r i e n t s except p r o t e i n and c a l c i u m . Protein was p r o v i d e d a t a m a r g i n a l (10%) o r e x c e s s i v e (30%) l e v e l w h i l e c a l cium was p r o v i d e d a t a s u b m a r g i n a l l e v e l . These l e v e l s r e p r e s e n t p a t t e r n s o f i n t a k e t y p i c a l o f t h e American p o p u l a t i o n . W i t h t h e e x c e p t i o n o f d i e t Β (10% p r o t e i n d i e t based e q u a l l y on p l a n t and a n i m a l p r o t e i n s o u r c e s ; T a b l e I ) , t h e body weight g a i n s of r a t s ( T a b l e I I ) were s i g n i f i c a n t l y h i g h e r ( T a b l e I I I ) when f e d 30% r a t h e r than 10% p r o t e i n d i e t s . Weight g a i n s on d i e t Β e q u a l l e d o r approached g a i n s o b s e r v e d on 30% p r o t e i n d i e t s ( d i e t s D - F ) . D i e t Β a l s o showed t h e h i g h e s t d i e t u t i l i z a t i o n e f f i c i e n c y as t h e d i e t : g a i n r a t i o s suggest ( T a b l e I I ) . I r r e s p e c t i v e o f t h e p r o t e i n s o u r c e s
Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Ory; Plant Proteins: Applications, Biological Effects, and Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
a
b
(5-Month E x p e r i m e n t )
245+23 2130+80 8.8+O.8 639+24 O.42+O.04 6389+240 8519+320 10.1+O.3 3.4+O.7 O.50+O.03 69.9+O.3 25.1+1.0 10.7+O.8
233+22 2034+105 8.7+O.4 610+32 O.45+O.04 6102+316 8134+420 10.1+O.4 3.3+O.3 O.48+O.04 70.2+O.8 26.0+O.4 10.7+O.6
205+14 2026+67 9.9+O.5 203+7 O.40+O.05 6078+200 8104+266 9.9+O.3 3.1+O.3 O.46+O.03 70.2+O.5 25.7+O.6 12.9+O.7
233+4 2003+52 8.6+O.3 200+5 O.37+O.03 6008+155 8011+207 9.9+O.4 3.3+O.3 O.48+O.04 69.9+O.6 25.1+2.0 12.4+O.5
214+17 1960+97 9.2+O.6 196+10 O.38+O.02
5880+291 7840+388 9.8+O.3 3.2+O.6 O.45+O.02 70.6+O.3 26.5+1.3 12.5+O.1 deviation.
Ε
D
C
3
Β
Diets
P h y s i o l o g i c a l Responses Of R a t s
A
II.
V a l u e s show a v e r a g e (9-10 r a t s p e r d i e t ) + s t a n d a r d 'Fat-free, moisture-free b a s i s .
b
b
Body wt. g a i n (g) D i e t i n t a k e (g) Diet:gain (ratio) P r o t e i n i n t a k e (g) Kidney wt. (g/100 g. wt. g a i n ) C a l c i u m i n t a k e (mg) Phosphorus i n t a k e (mg) Serum Ca (mg/dl) Serum Ρ (mg/dl) Femur d r y wt. (g) Femur a s h (%) Femur C a (%) Femur P (%)
Parameter
Table
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6333+281 8444+375 9.9+O.2 3.3+O.5 O.52+O.04 70.4+O.6 24.9+O.4 10.9+O.4
240+23 2111+94 8.8+O.5 633+28 O.42+O.04
F
9.
Effects of Protein on Skeletal Integrity
BOHANNON AND RANHOTRA
used, high p r o t e i n d i e t s - i n d u c e d ney ( T a b l e s I I and I I I ) . Table
III.
significant
103
enlargement of the k i d
S t a t i s t i c a l Analysis: F V a l u e s For Parameters I n c l u d e d In T a b l e I I a
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Level Body wt. g a i n Diet intake Diet : gain Protein intake Kidney wt. Ca i n t a k e Ρ intake Serum Ca Serum Ρ Femur wt. Femur ash Femur Ca Femur Ρ
:
20.2*** 18.6*** 10.5** 62.9*** 27.2*** 18.6*** 18.6*** 4.7 O.5 18.3*** O.6 2 3 143.4*** n s
ns
ns
n s
Dietary Type 4.3* 4.6** 7.2** 3.9* O.8 4.6* 4.6** O.8 O.5 3.4* 3.6* 6.6** 2.3 ns
ns
ns
n s
Protein L e v e l χ Type ns
1.8 O.6 6.0** 1.8 3.2* O.6 O.6 1.2 O.1 2.0 2.7 O.6 O.3 ns
ns
ns
ns
ns
ns
n s
n s
ns
ns
ns, not s i g n i f i c a n t *, P
