Two studies appear to show that taking in too much protein causes osteoporosis and so does taking in too little. Researchers at the University of California, San Francisco showed that elderly women who eat lots of meat have much greater loss of hip bone density and more hip fractures than those who eat primarily vegetable protein (1). This does not mean that vegetable protein is better; it is just very hard to get too much protein from vegetable sources because meat is a much more dense source of protein.
Taking in more animal protein than you need causes your body to convert extra protein building blocks called amino acids into organic acids that acidify the bloodstream. The kidneys neutralize the acidity by pushing large amounts of calcium into the urine. On the other hand, the Framingham Osteoporosis Study showed that women who didn't meet their needs for protein have severe bone loss over several years. So both eating too much protein and too little protein may cause osteoporosis.
The average person needs 60-75 grams of protein a day (one gram per kilogram of body weight.) There are no exact numbers, but too much protein is probably defined as more than three or four times this amount.
1) A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. DE Sellmeyer, KL Stone, A Sebastian, SR Cummings. American Journal of Clinical Nutrition, 2001, Vol 73, Iss 1, pp 118-122 Address: Sellmeyer DE, UCSF Prevent Sci Grp, 74 New Montgomery St, Suite 600, San Francisco,CA 94105 USA.
2) December 2000, Volume 15, Number 12. Page 2504. Effect of Dietary Protein on Bone Loss in Elderly Men and Women: The Framingham Osteoporosis Study* MARIAN T. HANNAN,1,2 KATHERINE L. TUCKER,3 BESS DAWSON-HUGHES,3 L. ADRIENNE CUPPLES,2 DAVID T. FELSON,2,4 and DOUGLAS P. KIEL1
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