Typically, loss of bone mass goes hand in hand with weight loss. This double-edged sword is a concern for middle-aged women, in particular. But results from a new study out of the University of Illinois (U of I), Urbana-Champaign, indicate a high-protein diet that includes lean meats and low-fat dairy foods as sources of protein can mean weight loss without bone loss.
For the study, published in the June 2008 issue of the Journal of Nutrition, 130 middle-aged, overweight subjects followed one of two diets: a high-protein, dairy-intensive weight-loss diet, or a weight-loss diet based on USDA’s food pyramid. Subjects followed the diets for four months of active weight loss, followed by eight months of weight maintenance.
"Essentially, we substituted lean meats and low-fat milk, cheese, yogurt, etc., for some of the high-carbohydrate foods in the food-pyramid diet. Participants also ate five servings of vegetables and two to three servings of fruit each day," said Ellen Evans, a U of I associate professor of kinesiology and community health, and member of the division of nutritional sciences.
At the beginning of the study, at 4 months, at 8 months, and at the end of the 12-month period, bone mineral content and density were measured for the whole body, lumbar spine and hip.
"In the higher-protein group, bone density remained fairly stable, but bone health declined over time in the group that followed the conventional higher-carbohydrate diet. A statistically significant treatment effect favored the higher-protein diet group," said Dr. Matthew Thorpe, a medical scholars student who was the primary author of the study. "The combination and/or interaction of dietary protein, calcium from dairy, and the additional vitamin D that fortifies dairy products appears to protect bone health during weight loss.”
Because higher-protein diets have been associated with elevated urinary calcium levels, the researchers measured these levels at the beginning, and at eight months. Although the researchers did note increased amounts of urinary calcium in the higher-protein group, they attributed the source of the increased calcium to improved intestinal absorption of calcium rather than bone loss.