Overweight and moderately obese postmenopausal women using diets based on higher protein intake also need to be aware of potential bone loss, according to new research from Purdue University.
"We know that when overweight, postmenopausal women reduce their energy intake to successfully lose weight, they can lose less lean body mass when they consume higher amounts of protein and include lean meats, such as pork loins, ham, beef and chicken, in their diet," said Wayne W. Campbell, professor of foods and nutrition. "However, we also found that these older women lost bone mineral density faster than women who consumed normal protein diets that did not contain any meats. This finding is of concern for this age group that is susceptible to osteoporosis."
Campbell and doctoral student Minghua Tang analyzed data from two controlled diet studies. In the first study, they reduced 28 women's individual daily diets by 750 calories to achieve a one-and-one-half-pound weight loss each week for 12 weeks. These postmenopausal women ranged in age from 43-80. Fifteen women consumed meat-free diets with protein from vegetarian, dairy and egg sources, comprising 18 percent of each woman's energy intake. This amount of protein was comparable to the recommended dietary allowance of 0.36 grams of protein per pound of body weight per day.
The diets for the other 13 women were composed of 30 percent of energy from protein with 40 percent of the protein from lean pork, such as loin and ham, and 60 percent of the protein from vegetarian, dairy and egg sources. The women, on average, lost about 19 pounds each, but those who ate the higher-protein, meat-containing diet lost bone mineral density.
In the second study, 43 postmenopausal women each ate a 1,250-calorie diet for nine weeks. All participants consumed the same 1,000-calorie vegetarian diet, but 15 women received 250 calories from chicken breast meat, 14 women received 250 calories from beef tenderloin and 14 women received 250 calories from shortbread cookies and sugar-coated chocolates. Another 11 women served as the control group. The researchers saw again that all of the women who ate the energy-reduced diets successfully lost weight, but the groups that consumed the higher-protein meat-containing diets also lost bone mineral density compared to the control group.
The bone mineral density was measured using a dual-energy X-ray absorptiometer.
The findings are published online in the Journal of Gerontology: Medical Sciences and will be printed in September.