Protein intake during weight loss: Effects on bone

Moderate weight loss not only reduces the comorbidities associated with obesity, but has also been shown to reduce bone mass. Supplementation with specific nutrients, such as calcium, may attenuate loss of bone mass during weight reduction. Recently, high-protein (HP) weight-loss diets have been shown to be as effective as, or sometimes more effective than, standard high carbohydrate weight loss diets in reducing symptoms associated with metabolic syndrome. The effect of higher protein diets on bone is important due to the greater acceptance among health care providers. Dietary protein has also been shown to have specific effects on the regulation of bone health. Some large epidemiological studies have shown a beneficial impact of protein on bone health, which is supported by intervention studies in patients with osteoporosis. In contrast, others have suggested that a HP diet is associated with low bone mineral density (BMD) and greater fracture risk and have attributed this to a greater acid load and increased urinary calcium excretion. Since lower calcium intake may mediate the negative effect of HP diets on bone, controlled trials to study the effects of protein are important. During weight reduction, there is both reduced calcium absorption and serum insulin-like growth factor-1 (IGF-1), which may contribute to bone loss, yet may be positively influenced by additional protein in the diet. The role of dietary protein during caloric restriction on bone health and potential mechanisms mediating these effects is reviewed.