In Overweight Adults, Calorie Restriction Alone Does Not Induce Bone Loss

A diet that is low in calories but still nutritionally substantial appears to incur weight loss and fat loss without significant bone loss in young adults, according to an article released on September 22, 2008 in Archives of Internal Medicine, one of the JAMA/Archives journals.

Biological aging can be slowed by calorie restriction. However, it is also known that chronic energy deficiency diminishes mineral uptake into bones, thereby weakening them. Previously, weight loss has been associated with bone loss in obese subjects. Since calorie restriction could lead to bone loss and fracture, it is important to understand if this is due to restriction of calories or rather of the vitamins that might accompany them.

To investigate the effects of calorie restriction without nutritional deficiency on bone mineral density, Leanne M. Redman, Ph.D., and colleagues at Pennington Biomedical Research Center, Baton Rouge, LA, examined healthy overweight men and women for 6 months. The 46 subjects were randomly assigned to one of four groups: a control group, assigned to a full healthy diet; a group consuming 25% fewer calories than the expended per day; a group consuming 25% energy deficit by both consuming fewer calories and exercising five days per week; and a group consuming a low calorie diet until they achieved 15% weight loss at which point they were transitioned to a weight-maintenance plan. All of the diets contained 30% fat, 15% protein, and 55% carbohydrates, and recommended levels of vitamins and minerals, including calcium. These values were determined based on American Heart Association guidelines.

In six months, the control group reduced its average body weight by 1%, the calorie restriction group reduced its average body weight by 10.4%, the calorie restriction group reduced its weight by 10%, and the low calorie diet group dropped its average body weight by 13.9%. 

Several markers of bone resorption and formation were examined over the course of the study. The authors summarize the results: "Compared with the control group, none of the groups showed any change in bone mineral density for total body or hip."
These resorption markers, indicating bone density loss, increased in all three intervention groups. Bone formation markers, however, decreased in the calorie restriction group but constant in the low-calorie diet and calorie restriction with exercise groups.

The authors conclude that this magnitude of weight loss is not detrimental for bone health. "Our data do not support the notion that extreme weight loss (more than 10 percent) over short periods (three months) has a worse prognosis on bone health than gradual weight loss achieved over six months by moderate calorie restriction with or without aerobic exercise," they say. However, they point out that the situation may be complicated by the changing stresses incurred with weight loss. "We speculate that in young individuals undergoing calorie restriction, minor adjustments in bone occur as a normal physiological adaptation to the reduced body mass. Further studies of longer duration are warranted and should include an assessment of bone architecture to ensure that bone quality is preserved with weight loss."

Calorie Restriction and Bone Health in Young, Overweight Individuals
Leanne M. Redman; Jennifer Rood; Stephen D. Anton; Catherine Champagne; Steven R. Smith; Eric Ravussin; for the Pennington Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE) Research Team
Arch Intern Med. 2008;168(17):1859-1866.
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Written by Anna Sophia McKenney