Osteoporosis Studies Courtesy Dr. Mirkin

[Guest guest]

" A high ratio of dietary animal to vegetable protein increases the

rate of bone loss and the risk of fracture in postmenopausal women. "

BACKGROUND: Different sources of dietary protein may have different

effects on bone metabolism. Animal foods provide predominantly acid

precursors, whereas protein in vegetable foods is accompanied by base

precursors not found in animal foods. Imbalance between dietary acid

and base precursors leads to a chronic net dietary acid load that may

have adverse consequences on bone.

OBJECTIVE: We wanted to test the hypothesis that a high dietary ratio

of animal to vegetable foods, quantified by protein content,

increases bone loss and the risk of fracture.

DESIGN: This was a prospective cohort study with a mean (+/-SD) of

7.0+/-1.5 y of follow-up of 1035 community-dwelling white women aged

>65 y. Protein intake was measured by using a food-frequency

questionnaire and bone mineral density was measured by dual-energy X-

ray absorptiometry.

RESULTS: Bone mineral density was not significantly associated with

the ratio of animal to vegetable protein intake. Women with a high

ratio had a higher rate of bone loss at the femoral neck than did

those with a low ratio (P = 0.02) and a greater risk of hip fracture

(relative risk = 3.7, P = 0.04). These associations were unaffected

by adjustment for age, weight, estrogen use, tobacco use, exercise,

total calcium intake, and total protein intake.

CONCLUSIONS: Elderly women with a high dietary ratio of animal to

vegetable protein intake have more rapid femoral neck bone loss and a

greater risk of hip fracture than do those with a low ratio. This

suggests that an increase in vegetable protein intake and a decrease

in animal protein intake may decrease bone loss and the risk of hip

fracture. This possibility should be confirmed in other prospective

studies and tested in a randomized trial.

PMID: 11124760

and:

" Effect of dietary protein on bone loss in elderly men and women: the

Framingham Osteoporosis Study. "

Few studies have evaluated protein intake and bone loss in elders.

Excess protein may be associated with negative calcium balance,

whereas low protein intake has been associated with fracture. We

examined the relation between baseline dietary protein and subsequent

4-year change in bone mineral density (BMD) for 391 women and 224 men

from the population-based Framingham Osteoporosis Study. BMD (g/cm2)

was assessed in 1988-1989 and in 1992-1993 at the femur, spine, and

radius. Usual dietary protein intake was determined using a

semiquantitative food frequency questionnaire (FFQ) and expressed as

percent of energy from protein intake. BMD loss over 4 years was

regressed on percent protein intake, simultaneously adjusting for

other baseline factors: age, weight, height, weight change, total

energy intake, smoking, alcohol intake, caffeine, physical activity,

calcium intake, and, for women, current estrogen use. Effects of

animal protein on bone loss also were examined. Mean age at baseline

(+/-SD) of 615 participants was 75 years (+/-4.4; range, 68-91

years). Mean protein intake was 68 g/day (+/-24.0; range, 14-175

g/day), and mean percent of energy from protein was 16% (+/-3.4;

range, 7-30%). Proportional protein intakes were similar for men and

women. Lower protein intake was significantly related to bone loss at

femoral and spine sites (p < or = 0.04) with effects similar to 10 lb

of weight. Persons in the lowest quartile of protein intake showed

the greatest bone loss. Similar to the overall protein effect, lower

percent animal protein also was significantly related to bone loss at

femoral and spine BMD sites (all p < 0.01) but not the radial shaft

(p = 0.23). Even after controlling for known confounders including

weight loss, women and men with relatively lower protein intake had

increased bone loss, suggesting that protein intake is important in

maintaining bone or minimizing bone loss in elderly persons. Further,

higher intake of animal protein does not appear to affect the

skeleton adversely in this elderly population.

PMID: 11127216

Rodney.