Researchers from Perdue University tested the effect on bone mineral density (BMD) of high-protein diets based on both meat and non-meat sources of protein.
"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."
The findings, due to be published in September in the Journal of Gerontology: Medical Sciences, were based on two studies supported by The National Pork Board and National Institutes of Health together with the Beef Checkoff program.
Study 1
In the first study, 28 overweight post-menopausal women (aged 43 to 80) were divided into two groups. Both groups had their daily diets reduced by 750 calories to achieve a one-and-one-half-pound weight loss each week for 12 weeks.
The first group, comprised of 15 women, was given a meat-free diet with protein from vegetarian, dairy and egg sources, which made up18 percent of each woman's energy intake and was comparable to the recommended dietary allowance of 0.36g of protein per pound of body weight per day.
The second group of 13 women followed diets 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 researchers found that on average, all women lost around 19 pounds, but those who ate the higher-protein, meat-containing diet also lost bone mineral density by about 1.4 percent.
Study 2
The second study involved 43 postmenopausal women, who 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.
All women lost weight, but the groups that consumed the higher-protein meat-containing diets again also lost bone mineral density by up to 1.4 percent compared to the control group.
No impact from calcium supplements
In the first study, all the participants consumed calcium supplements to achieve calcium intakes of 2,000mg per day. In the second study, about half of the participants consumed calcium supplements.
However, in neither case were the supplements found to impact the loss of bone density.
“Collectively, higher calcium intakes from supplements do not appear to prevent or influence the loss of BMD when overweight and obese postmenopausal women lose weight while consuming a higher protein omnivorous diet,” wrote the researchers.
Bone loss
“In summary, a higher protein energy-restricted diet with protein predominantly from animal flesh sources promoted total body BMD loss in overweight and obese postmenopausal women during weight loss compared with a lower protein energy-restricted diet void of animal flesh foods,” wrote the researchers.
“Our results suggested that for postmenopausal women, choosing a higher protein omnivorous diet for effective weight loss, may decrease BMD and increase the risk of osteoporosis.”
Source: Protein Intake, Weight Loss, and Bone Mineral Density in Postmenopausal Women
J Gerontol A Biol Sci Med Sci
doi:10.1093/gerona/glq083
Authors: Wayne Campbell; Minghua Tang