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Obese postmenopausal women lost significantly more weight on a severely calorie-restricted diet than those on a more moderate diet, but the former also lost more bone mineral density (BMD), clinical trial investigators reported.

Compared with the moderate diet group, the severely restricted diet group lost more overall body weight (effect size -6.6 kg, 95% CI -8.2 to -5.1) and whole-body fat mass (effect size -5.5 kg, 95% CI -7.1 to -3.9), said researchers led by Radhika Seimon, PhD, of the University of Sydney in Australia.

However, as they reported online in , the group on the severely restricted diet also lost more total hip BMD over the course of the 12-month intervention (effect size −0.017 g/cm², 95% CI −0.029 to −0.005 ). The severe dieters also lost more whole-body lean mass and thigh muscle mass, but these were proportional to their total weight loss. Muscle strength as measured by handgrip did not differ between the two groups, Seimon and colleagues said.

Participants on the severe diet were three times less likely to discontinue the trial compared with those on the moderate diet, the researchers found, explaining that this may be because the substantial and rapid weight loss was encouraging and the total meal replacement program was simple and convenient to use.

"The consequences of accelerated BMD loss with a severely energy-restricted dietary obesity treatment are clinically concerning, especially if BMD loss continues beyond the 12-month intervention, because it has been linked to an increased risk of osteoporosis and fragility fracture," Seimon's group wrote. "However, this bone loss must be considered in light of the beneficial effects of substantial weight loss on other health outcomes and healthcare costs."

For example, the team noted, a 3-5% loss of body weight has generally been accepted as clinically significant, and recent research has shown that greater weight loss improves health outcomes in a dose-dependent manner.

"In addition, if treated effectively, the costs of obesity-related health complications would be significantly reduced," the researchers added. "Thus, while the current trial should not discourage the use of total meal replacement diets as a treatment for obesity in postmenopausal women, further investigation is needed to determine the long-term consequences of the associated BMD loss on health outcomes such as osteoporotic fractures and to determine how BMD losses could be prevented in this population during and after these diets."

'Consider in Context'

Writing in an , Marinka Steur, PhD, of the University of Cambridge in the U.K., agreed that the loss of BMD should be considered in light of the benefits of weight loss: "Seimon et al now advance the literature by providing one of the first direct comparisons of severe vs moderate caloric restriction," Steur wrote. "Nevertheless, these findings need to be considered in the context of an ever-increasing obesity epidemic and the various obesity-related adverse health outcomes, including type 2 diabetes, cardiovascular diseases, and all-cause mortality."

Increasing evidence suggests that greater weight loss can help achieve type 2 diabetes remission, Steur continued. "Finding strategies successful at achieving sustained weight loss in individuals with obesity should be an absolute priority in public health research. The TEMPO Diet Trial now adds to accumulating evidence that VLEDs [very low-energy diets] can help achieve greater weight loss than moderate dietary interventions alone, well after the use of VLEDs is ended."

The trial included 101 obese postmenopausal women with a mean age of 58 and mean body mass index of 34.4. They were randomized to either a moderately energy restrictive diet (25-35% reduction) based on the Australian Guide to Healthy Eating or the severely restricted diet (65-75% reduction) that included meal-replacement soups and shakes and a protein bar. The moderate intervention continued for 12 months, while the severe intervention lasted only 4 months, after which participants switched to the moderate diet for 8 months.

The severe diet provided 1,200 milligrams of calcium and 15 micrograms of vitamin D daily. Both diets had a prescribed protein intake of 1 gram per kilogram of body weight per day. Physical activity was encouraged for both groups but not supervised.

Two key limitations of the study were that data on participants' physical activity and actual dietary intake were not presented, Steur said. "This leaves us to speculate not only about adherence to the intervention diets, but also on how nutrient intake levels compared between groups. Additionally, biomarker data, such as circulating 25-hydroxyvitamin D levels, could have provided valuable information about effects on nutritional status."

The study authors urged caution when implementing severely restrictive diets in postmenopausal women -- "especially in those with osteopenia or osteoporosis, for whom concurrent bone-strengthening treatments (e.g., muscle strengthening exercises) are recommended."

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