Q and A

Protein: Bad to the Bone?

 

Is there a concern regarding high protein intake and calcium loss?

Earlier reports suggested an association between a high protein intake with increased calcium excretion. The consumption of animal protein, which is higher in sulfur-based amino acids than vegetable proteins, which is now known to be incorrect, [1] and was the proposed mechanism likely related to the increase in acid secretion due to the elevated protein consumption.



Bone acts as a reservoir of alkali. If the kidneys are unable to buffer the high endogenous acid levels, other physiological systems such as bone will need to compensate. Calcium is liberated from bone to buffer high acidic levels and restore acid-base balance. The loss or removal of bone will cause a decline in bone mineral content and bone mass increasing the risk for bone fracture and osteoporosis.

However, no studies have been able to link a cause and effect association regarding a high protein diet and calcium loss. In fact, most well controlled studies suggest the opposite. That is, older female populations have shown that elevated animal protein will increase bone mineral density, while increases in vegetable protein will have a lowering effect on bone mineral density [2,3].

Munger and colleagues (1999) also reported a 69% lower risk of hip fracture as animal protein intake increased in a large (32,000) postmenopausal population. Other large epidemiological studies have also confirmed elevated bone density following high protein diets in both elderly men and women [4,5] ). Hannan and colleagues (2000) demonstrated that animal protein intake in an older population, several times greater than the RDA requirement, results in a bone density accruement and significant decrease in fracture risk.

Dawson-Hughes et al. (2002), not only showed that animal protein will not increase urinary calcium excretion, but was also associated with higher levels of IGF-I and lower concentrations of the bone resorption marker N-telopeptide. It is likely that other factors play important roles in further understanding the influence that dietary proteins have on bone metabolism. Dietary calcium intake is one, the type of physical activity (or lack of) is another. As well as genetic factors such the absence of a vitamin D receptor allele.

Recommended reading: Protein - can you have too much?

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1. Massey, L.K. (2003) Dietary animal and plant protein and human bone health: a whole foods approach. Journal of Nutrition 133, 862S-865S.

2. Munger, R.G., Cerhan, J.R. and Chiu, B.C.H. (1999) Prospective study of dietary protein intake and risk of hip fracture in postmenopausal women. American Journal of Clinical Nutrition 69,147-52.

3. Promislow, J.H.E., Goodman-Gruen, D., Slymen, D.J. and Barrett-Connor, E. (2002) Protein consumption and bone mineral density in the elderly. American Journal of Epidemiology 155, 636-644.

4. Dawson-Hughes, B. (2003) Calcium and protein in bone health. Proclamations of the Nutrition Society 62, 505-509.

5. Hannan, M.T., Tucker, K.L., Dawson-Hughes, B., et al. (2000) Effect of dietary protein on bone loss in elderly men and women: The Framingham Osteoporosis Study. Journal of Bone Mineral Research 15, 2504-2512.





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