To fight the battle of the bulge, many are turning to diets that emphasize protein.
By volume, bone is 50 percent mineral, 64 percent of which is calcium. Protein makes up most of the remaining 50 percent. A large percentage of the amino acids in bone collagen is trapped and unable to be used for new protein synthesis. Therefore, proper osseous turnover requires regular ingestion of adequate amounts of dietary protein.1
It has been known for many years that dietary protein increases urinary calcium losses.2 Dr. Stephanie Atkinson, a calcium expert from McMaster University in Canada, states that for each gram of protein consumed, we excrete 1-1.5 mg of calcium in our urine. If a woman eats 70 grams of protein per day, her urinary calcium losses will range from 70 to 105 mg of calcium. This may seem like an insignificant amount, given that the RDA for calcium is 1,200 mg for women over 50. However, the average American only consumes 600 mg of calcium per day.3 Subtract 100 mg from the average diet, and it is clear that protein can have a significant effect on bone health. In a recent paper, researchers found that high protein intakes were associated with an increased risk of fracture, but only if dietary calcium intakes were low (less than 400 mg per day).4
Studies have shown that premenopausal and postmenopausal women with high total protein intakes and high animal-to-vegetable-protein ratios have a higher incidence of fractures.5,6 In contrast, other studies have conflicted with these findings and have shown that higher dietary protein intakes are associated with reduced fracture risk in postmenopausal women.7 In one study of geriatric patients recovering from hip fractures, the group given 20 grams of protein supplements per day for one year, along with calcium and vitamin D, showed greater improvement in bone mineral density than the calcium and vitamin D group that received no extra protein.8
Part II will expand on this topic and take an in-depth look at a large, three-year, randomized controlled trial on calcium, vitamin D, and how protein affected the bone density of over 300 healthy men and women 65 years of age and older.References
- Heaney RT. Protein and calcium: antagonists or synergists? Am J Clin Nutr 2002;75:609-10.
- Heaney RP, Recker RR. Effects of nitrogen, phosphorus, and caffeine on calcium balance in women. J Lab Clin Med 1982;99:46-55.
- Liebman B. Bare bones. Nutrition Action Health Letter 2002;29:1-8.
- Meyer HE, Pedersen JI, et al. Dietary factors and the incidents of hip fracture in middle-aged Norwegians. Am J Epidemiol 1997;145:117-23.
- Sellmeyer DE, Stone KL, et al. A high ratio of dietary animal-to-vegetable-protein increases the rate of bone loss and risk of fracture in postmenopausal women. Am J Clin Nutr 2001;73:118-22.
- Feskanich D, Willet WC, et al. Protein consumption and bone fractures in women. Am J Epidemiol 1996;143:472-9.
- Munger RG, Cerhan JR, Chiu BC. Prospective study of dietary protein and risk of hip fracture in postmenopausal women. Am J Clin Nutr 1999;59:147-5q.
- Schurch MA, Rizzoli R, et al. Protein supplements increase serum insulin-like growth factor-1 levels and attenuate proximal femur bone loss in patients with recent hip fracture. Ann Intern Med 1998;128:801-9.
G. Douglas Andersen,
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