The prevalence of obesity is increasing yearly, and diet-induced weight loss is the primary treatment option. Clinicians treating obesity may hesitate to use very-low energy diets due to potential adverse effects such as reduced lean mass that could reduce muscle strength, and reduced bone mineral density (BMD). In a recent meta-analysis we found a loss of hip BMD in response to diet-induced weight loss in overweight/obese individuals1. We therefore compared the short-term effects of fast versus slow weight loss on muscle strength and BMD in a randomised controlled trial.
This preliminary analysis included 31 obese post-menopausal women (BMI 34.0±2.5 (SD) kg/m2, age 56.8±4.1 years). Participants were randomised to either 16 weeks of FAST or SLOW weight loss (70% or 30% energy restriction, respectively). To help preserve lean mass, protein supplement was added to the VLED so both diets had a protein intake of 1g/kg body weight per day. Body weight, muscle strength (JAMAR hand dynamometer), total hip and spine BMD (Hologic Discovery Dual-energy X-ray absorptiometry) were measured at 0 (baseline) and 16 weeks after commencing energy restriction.
The FAST group lost more weight than the SLOW group (FAST: 18.9±4.0%, SLOW: 7.1±3.1% of baseline body weight; P<0.001). Compared to baseline, there was no short-term effect of either diet on muscle strength (FAST: 2.9±12.0%; SLOW: 1.1±12.0%) or BMD (Hip: FAST: -1.5±4.0%; SLOW: 0.0±3.7%; Spine: FAST: -1.5±2.8%; SLOW: -1.1±2.8%), and no difference in muscle strength (P=0.7) or BMD (Hip: P=0.3; Spine: P=0.7) between groups.
These preliminary findings suggest there is no short-term adverse effect of fast or slow weight loss on muscle strength or BMD when protein intake is adequate, despite fast weight loss inducing a 2.5-fold greater weight loss. In terms of muscle strength and bone density, fast weight loss with adequate protein intake is thus a valid obesity treatment option.