Though weight loss can often lead to bone loss, particularly in high-risk groups, a new high-protein, low-fat dairy diet can prevent this, say researchers.

"Many people lose bone mass when they lose weight," said Ellen Evans, an associate professor of kinesiology and community health at the University of Illinois. This can become an issue for middle-aged people, particularly women, who want to lose weight — but could sabotage their bone mass.

Researchers studied 130 middle-aged people who were divided into two groups. One was instructed to follow a higher-protein weight loss diet or a higher carbohydrate weight-loss diet for four months of weight loss. This was followed by eight months of weight maintenance.

In the higher protein diet, high carbohydrate foods were substituted with low-fat milk, cheese and yogurt.

The study participants also consumed five servings of vegetables and two-to three servings of fruit daily.

At four months, eight months and at the end of the 12-month period, bone mineral content and density were measured with Dual energy X-ray absorptiometry (DEXA) scans. At 12 months, the bone density  was higher by 1.6 per cent for the whole body in the high-protein group than in the carbohydrate group, 2.1 per cent higher in the lumbar spine, and 1.4 per cent higher in the hips.

"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," said Matthew Thorpe, the primary author of the study.

He believes that the interaction of the protein with the higher calcium intake along with the extra vitamin D contained in dairy products seems to protect against bone loss.

The researchers next plan to study how a higher-protein, high-dairy diet will affect women at high risk of osteoporosis.

The study is published in the June issue of the Journal of Nutrition.