Diets that focus on increasing protein and calcium intake might curb some of the bone loss that typically accompanies weight loss, reports a study in the Journal of Nutrition. The study’s authors point out that “as an aging population confronts concurrent threats of obesity and osteoporosis, diets that promote weight loss while maintaining bone mineral mass and density are of special interest.”
Protein and bone health
Large amounts of dietary protein can cause calcium to be lost in the urine, which raises concerns about the effects of high-protein diets on bone health. However, recent evidence suggests that eating more protein might actually increase calcium absorption, offsetting those losses.
Weight loss of 10% may be accompanied by 1 to 2% of bone loss, increasing the risk of osteoporosis and fractures. Researchers from the University of Illinois and Pennsylvania State University set out to see if bone loss could be modified depending on the type of weight loss diet that was followed.
Putting a high-protein diet to the test
For one year, 130 middle-aged, overweight people were asked to follow one of these diets, each of which provided the same number of daily calories:
• a high-protein, dairy-rich diet providing 0.64 grams of protein per pound of body weight and three servings of dairy per day (roughly 30% protein, 40% carbohydrate, and 30% fat)
• a high-carbohydrate diet providing 0.36 grams of protein per pound of body weight and two servings of dairy per day (about 15% protein, 55% carbohydrates, and 30% fat)
Both diets led to weight loss, with no differences between the groups. Calcium intakes were significantly greater in the high-protein diet group; women in the high-carbohydrate diet did not meet recommended intake levels.
Urinary calcium losses were greater in the high-protein diet group than in the high-carbohydrate group, but measures of bone density were greater in the protein group. By the end of the study, bone mineral densities at various sites in the body were significantly greater in the high-protein group than in the high-carbohydrate group.
“A higher protein weight loss diet emphasizing dairy as a lean protein source naturally improved calcium intake and preserved bone mineral density during weight loss relative to a conventional higher carbohydrate diet,” said the authors.
A combined approach is best for weight loss
• When dieting, make sure to get at least 30 minutes of moderate-intensity exercise on most days of the week. This helps prevent bone loss and strengthen the muscles needed to prevent falls that can lead to bone breaks.
• Women and men ages 19 to 50 should aim for about 1,000 mg of calcium per day. People over age 50 should get 1,500 mg of calcium every day to prevent deficiency.
• Focus on calcium-rich, lean protein sources like low-fat yogurt and milk. Almonds, northern beans, lentils, navy beans, and tofu are packed with protein and calcium and make great alternatives to dairy-based calcium sources.
“There are so many weight loss diets out there, it’s hard to know which one is right for me,” commented Gailjean Gallon, a nurse in Baltimore, Maryland. “It’s good to know that losing weight doesn’t have to mean jeopardizing my bones.”
(J Nutr 2008;138:1096–100)
Kimberly Beauchamp, ND