The pathology of osteoporosis involves a combination of many risk factors and physiological variables such as macro nutrient intakes (carbs, proteins, fats), micro nutrient intakes (vitamins, minerals, etc), hormonal profiles, lack of exercise, gender, family history, and a few others.
The theory is that high protein intakes raise the acidity of the blood and the body must use minerals from bone stores to “buffer” the blood and bring the blood acidity down, thus depleting one’s bones of minerals. Though some early studies appeared to show higher protein intakes caused an excretion of calcium, which would ultimately lead to bone loss, recent studies have debunked that assertion and do not support the claim that higher than RDA intakes of protein will lead to bone loss ("Excess dietary protein may not adversely affect bone.” J Nutr 1998 Jun;128(6):1054-7).
Even if there was a clear link between a high protein diet and osteoporosis in all populations (and there is not) athletes have few of the above risk factors as they tend to get plenty of exercise, calories, minerals, vitamins, and have positive hormonal profiles.
Fact of the matter is, studies have shown athletes to have denser bones than sedentary people, there are millions of athletes who follow high protein diets without any signs of premature bone loss, and we don’t have ex athletes who are now older with higher rates of osteoporosis. What about regular people? One prominent researcher did an exhaustive review of the literature called “Optimal Intakes of Protein in the Human Diet” (Millward DJ .Proc Nutr Soc 1999 May;58(2):403-13) and came to some interesting conclusions on the issue. The study outlined an extensive body of recent data showing that high protein diets may in fact be beneficial for reducing blood pressure and stroke mortality. On the matter of bone loss, the review paper concludes “For bone health the established views of risk of high protein intakes are not supported by newly-emerging data, with benefit indicated in the elderly.”
Interestingly, a large body of research is now showing that the elderly may in fact require higher intakes of protein that is currently being recommended ("Increased protein requirements in elderly people: new data and retrospective reassessments.Am J Clin Nutr 1994 Oct;60(4):501-9).
