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National Dairy Council, Rosemont, IL 60018-5616 and * Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47907-1264
2To whom correspondence should be addressed. E-mail: lisas{at}rosedmi.com
This preface along with the following three reviews and summary present the proceedings of the Nutrition and Bone Health Working Group of the American Society for Bone and Mineral Research held in San Antonio, TX on September 20, 2002. The purpose of the program was to educate both researchers and practitioners through interactive presentations of recent research in the area of dietary protein and bone health by leading scientists.
Dr. Rene Rizzoli of the Division of Bone Diseases, Department of Internal Medicine at University Hospitals Geneva, introduced the speakers: Dr. Bess Dawson-Hughes, Dr. Jane Kerstetter and Dr. Linda Massey. A panel discussion followed the presentations. The summary, written by Dr. Zamzam K. (Fariba) Roughead, captures the speaker and participant comments generated from the presentations and the panel discussion.
The relationship between dietary protein and bone health has long been a controversial topic. Although protein is known to be essential to bone health, the calcium-wasting effect of protein has remained a point of debate. Several lines of evidence demonstrate the beneficial role of protein on bone health. The intake of calcium- and protein-rich foods such as dairy foods during childhood and adolescence is an important contributor to peak bone mass (1 –4 ). Calcium and protein are also crucial for maintenance of bone mass and prevention of bone loss in adults (5 –7 ). Adequate protein intake is a major factor in recovery after hip fracture (8 ). Protein supplementation of elderly hip-fracture patients has been shown to improve outcomes with fewer deaths, less permanent institutionalization and higher return to independent living (6 ,9 ).
Despite the benefits of protein to bone health, dietary protein has been shown to increase urinary calcium resulting from an increase in bone resorption (10 ). This calciuric effect of protein is the result of the increased acid load on the kidney created from the metabolism of amino acids, which is buffered by bone (11 ). The skeleton, along with being a labile reservoir of calcium, is a reservoir of alkaline salts of calcium, which provide a source of labile base that can be used to react to blood pH and plasma bicarbonate concentrations (12 ). Bone loss may be attributable, in part at least, to the life-long mobilization of skeletal salts to balance the endogenous acid generated from foods that are acid producing (13 ). Others have proposed that bone resorption is independent of the acid–base theory (14 ).
Although the calciuric effect of protein is evident, some studies indicate that high protein intake in humans does not significantly affect calcium absorption, urinary calcium, fecal calcium or calcium balance (15 –18 ). In those studies where urinary calcium did not significantly increase, this result was likely attributable to the higher phosphorus content associated with the high protein intakes, causing calcium reabsorption at the kidney (15 ,17 ,18 ). Furthermore, early investigations into the relationship of dietary protein and bone health demonstrate that low protein intakes cause little change in urinary calcium, whereas calcium absorption, fecal calcium and calcium balance remain unchanged (15 ). Although all stages of the life cycle should be considered in the discussion of dietary protein and bone health, the main focus has been on the elderly population, among which excessive protein consumption is unlikely.
Although protein is an important contributor to bone health, interactions of protein with other nutrients in the total diet have the greatest influence on the skeleton. The objective of this collection of papers is to present data on the interactions of calcium, protein and other nutrients on bone health. Additionally, the papers address the role of the whole diet in influencing bone health and highlight recent work that indicates the possible detriment of low protein intakes on bone health.
Bess Dawson-Hughes presents evidence on the interaction of dietary calcium and protein in bone health. This interaction may be the critical factor influencing bone mass and fracture risk. Through increases in dietary calcium, the impact of dietary protein on urinary calcium may be neutralized, thus allowing protein to contribute to bone health by stimulating production of insulin-like growth factor-1.
Jane Kerstetter provides provocative research, which demonstrates a role of dietary protein in affecting intestinal calcium absorption. Results from a series of nutrition interventions from her laboratory have been contrary to the traditional hypothesis that high protein diets increase bone resorption and thus skeletal fracture. Her data show that low protein diets, compared to high protein diets, induce a reduction in intestinal calcium absorption that is accompanied by secondary hyperparathyroidism. However, this effect may be transient. On the other hand, recent epidemiological studies (19 –21 ) demonstrate decreases in bone density and increases in rates of bone loss in individuals who habitually consume low protein diets. In the Framingham Osteoporosis Study, protein, magnesium, potassium and fruit and vegetable intakes were all significantly associated with baseline bone mineral density in both men and women and lower bone loss in men over 4 y (22 ). Thus, questions about the detrimental effect of low protein diets on bone health are raised.
Linda Massey presents the concept of a whole foods approach in determining the role of dietary protein, animal vs. plant, on bone health. The effects of dietary protein on bone health are modified by other nutrients present in protein food sources. Excess dietary proteins, whether from animal or plant sources, may be detrimental to bone health, but nutrients such as calcium, potassium, phosphorus and vitamin D can influence the effects of protein. Thus, it is important to consider the whole food and entire diet when delineating the role that dietary protein plays on bone health.
The following reviews discuss each of these issues in great detail. The summary highlights both the consensus and the controversy that remain in the area of dietary protein and bone health.
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LITERATURE CITED |
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 TOP LITERATURE CITED |
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6. Delmi, M., Rapin, C. H., Bengoa, J. M., Delmas, P. D., Vasey, H. & Bonjour, J. P. (1990) Dietary supplementation in elderly patients with fractured neck of the femur. Lancet 335:1013-1016.[Medline]
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8. Heikinheimo, R. J., Inkovaara, J. A., Harju, E. J., Haavisto, M. V., Kaarela, R. H., Kataja, J. M., Kokko, A. M., Kolho, L. A. & Rajala, S. A. (1992) Annual injection of vitamin D and fractures of aged bones. Calcif. Tissue Int. 51:105-110.[Medline]
9. Bastow, M. D., Rawlings, J. & Allison, S. P. (1983) Benefits of supplementary tube feeding after fractured neck of femur. Br. Med. J. 287:1589-1592.
10. Barzel, U. S. & Massey, L. K. (1998) Excess dietary protein can adversely affect bone. J. Nutr. 128:1051-1053.
11. Bleich, H. L., Moore, M. J., Lemann, J., Jr, Adams, N. D. & Gray, R. W. (1979) Urinary calcium excretion in human beings. N. Engl. J. Med. 301:535-541.[Medline]
12. Wachman, A. & Bernstein, D. S. (1968) Diet and osteoporosis. Lancet 1:958-959.[Medline]
13. Bushinsky, D. A. (1998) Acid–base imbalance and the skeleton. Burckhardt, P. Dawson-Hughes, B. Heaney, R. P. eds. Challenges of Modern Medicine 1998:208-217 Ares-Serono Symposia Publications Rome, Italy. .
14. Muhlbauer, R. C., Lozano, A. & Reinlis, A. (2002) Onion and a mixture of vegetables, salads, and herbs affect bone resorption in the rat by a mechanism independent of their base excess. J. Bone Miner. Res. 17:1230-1236.[Medline]
15. Spencer, H., Kramer, L., Osis, D. & Norris, C. (1978) Effect of a high protein (meat) intake on calcium metabolism in man. Am. J. Clin. Nutr. 3:2167-2180.
16. Spencer, H., Kramer, L., DeBartolo, M., Norris, C. & Osis, D. (1983) Further studies of the effect of a high protein diet as meat on calcium metabolism. Am. J. Clin. Nutr. 37:924-929.
17. Spencer, H., Kramer, L. & Osis, D. (1988) Do protein and phosphorus cause calcium loss?. J. Nutr. 118:657-660.
18. Hunt, J. R., Gallagher, S. K., Johnson, L. K. & Lykken, G. I. (1985) High- versus low-meat diets: effects on zinc absorption, iron status, and calcium, copper, iron, magnesium, manganese, nitrogen, phosphorus, and zinc balance in postmenopausal women. Am. J. Clin. Nutr. 62:621-632.
19. Hannan, M. T., Tucker, K. L., Dawson-Hughes, B., Cupples, L. A., Felson, D. T. & Kiel, D. P. (2000) Effect of dietary protein on bone loss in elderly men and women: the Framingham Osteoporosis Study. J. Bone Miner. Res. 15:2504-2512.[Medline]
20. Promislow, J. H., Goodman-Gruen, D., Slymen, D. J. & Barrett-Connor, E. (2002) Protein consumption and bone mineral density in the elderly: the Rancho Bernardo Study. Am. J. Epidemiol. 155:636-644.
21. Munger, R. G., Cerhan, J. R. & Chiu, B. C. (1999) Prospective study of dietary protein intake and risk of hip fracture in postmenopausal women. Am. J. Clin. Nutr. 69:147-152.
22. Tucker, K. L., Hannan, M. T. & Kiel, D. P. (2001) The acid–base hypothesis: diet and bone in the Framingham Osteoporosis Study. Eur. J. Nutr. 40:231-237.[Medline]
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