Does (Animal) Protein Leach Calcium from Bones?
[Thank you for all the responses to my request for information on increasing bone mineral density! I received a lot of responses and am still working my way through them.]
Because I’m planning to write a more reader-friendly version of VeganHealth.org’s Bones, Vitamin D, and Calcium, I decided to check in on the research on protein and bone health. In so doing, I found a 2012 review from a group of researchers in France who declared having no conflicts of interest (1).
There has been an enormous amount of research on protein and bone health and their review had almost 4 pages of references. I will hit the highlights of what they found:
– Many clinical trials show that adding purified proteins to the diet increases calcium excretion through the urine.
– Phosphorus, in which meat and dairy are rich, counteracts the increase of calcium in the urine between 40 and 65%.
– Findings that older people in Western countries have higher hip fracture rates are confounded by the fact that people in Western countries live longer, protein intakes were not estimated for individuals, and there are ethnic differences in bone structure and lifestyles.
– High protein diets increase acid excretion in the urine, but this can be handled by the body’s acid buffer system without the need for calcium.
– Studies measuring whole-body calcium balance (as distinct from excretion) in relation to high protein diets have been mixed, but this might partly be due to the difficulty in measuring calcium balance and because high protein diets might reduce calcium balance when calcium intakes are particularly low.
– In low-calcium, but not high-calcium diets, higher protein intakes probably increase calcium absorption from the digestive tract causing an increase in calcium excretion in the urine.
– Fruits and vegetables are beneficial to bone health, probably due to their high potassium and magnesium content. This could cause confounding in protein studies because diets high in protein are often low in fruits and vegetables.
– As I describe in my post Protein Intake and Bone Health, Darling et al. (2009) found that a large majority of the cross-sectional surveys and cohort studies have reported either no association or a beneficial association between protein and bone mineral density.
– There is some evidence that a beneficial effect of protein on bones is only seen when calcium intake and vitamin D status is adequate.
– Maintenance of adequate bone strength and density with aging is dependent on adequate muscle mass which is dependent on adequate intake of protein.
– An increase in IGF-1 is most likely the mechanism for increased bone health with higher protein intakes.
They conclude, “Although HP [high protein] diets induce an increase in net acid and urinary calcium excretion, they do not seem to be linked to impaired calcium balance and no clinical data support the hypothesis of a detrimental effect of HP diet on bone health, except in the context of inadequate calcium supply.”
1. Calvez J, Poupin N, Chesneau C, Lassale C, Tomé D. Protein intake, calcium balance and health consequences. Eur J Clin Nutr. 2012 Mar;66(3):281-95. | link