There's conflicting evidence about the role protein plays in bone health, Jeannette Beasley from the Group Health Research Institute in Seattle, Washington and colleagues note in their report. Protein in the diet from animal and vegetable sources is important to the development of strong bones. Yet, when protein from animal sources is digested, chemicals known to lead to bone loss are produced.
To see if there might be a tipping point at which the risks of a diet too high in protein outweigh the benefits for bone health, Beasley's team analyzed data from two large studies that looked at diet, lifestyle, and bone density in 560 women aged 14 to 40.
A typical American diet derives 10 to 15 percent of total calories from protein. In a high-protein diet, total protein calories can range from 30 to 50 percent. Protein consumption among women in the two studies ranged from a low of about 6 percent to a high of about 28 percent of total calories.
Beasley's team found that increasing protein intake did not lead to a "significant" change over time in bone density, leading them to conclude that protein intake in the "upper range of typical consumption" in the United States does not negatively affect bone health in premenopausal women.
This study appears to extend to younger women the finding of a recent analysis of 61 studies of older women that "there is a small benefit of protein on bone health, but the benefit may not necessarily translate into reduced fracture risk in the long term," Beasley told Reuters Health in an email.
That's important because "findings in young women could be different from those in older women because bone mass is still building up before age 30," Beasley said.
In the current study, higher protein intake "seemed to be more beneficial for boosting (bone density) for women age 14 to 29 years compared to those age 30 to 40 years, who have already reached their peak bone mass," Beasley pointed out.
The population of women in the analysis was predominantly non-Hispanic white. As a result, the investigators caution against applying the results to other racial-ethnic groups "with differences in bone metabolism."
The study does not speak to the risks or benefits of popular high-protein diets such as the Atkins and Zone diets, which typically have protein intake above 35 percent of total calories, Beasley noted, which is outside the dietary recommendation of 10 to 35 percent spelled out by the Institute of Medicine.
Beasley said the study findings support adoption of a well-rounded diet throughout life.
"Protein is a major constituent of bone. Consuming a nutrient-rich diet is important for building and maintaining strong bones throughout your life," she said.
SOURCE: American Journal of Clinical Nutrition, March 2010