It’s well-documented that weight loss is a function of energy balance; if you expend more calories than you consume, you lose weight. However, the composition of the weight lost is very important. In many diet strategies, 25% or more of weight loss comes from lean mass (primarily muscle tissue). Not only is this detrimental to both physical function and appearance, but it actually has negative effects on fat accumulation over the long-term.
Here’s the issue: Lean mass is essential to survival. When you lose lean mass (muscle), the body thus perceives a threat to its survival and overcompensates through neural/hormonal triggers that increase hunger and reduce metabolic rate in an attempt to restore the lean mass that had been lost. Ultimately, the alterations in these factors persist so that additional fat mass is gained, over and above what you had before dieting – the so-called “fat overshooting” hypothesis.
Although the strategies for losing fat while preserving lean mass are complex, the obvious first line of defense is to lift weights. It is the single most important activity you can do to avoid a loss of muscle during dieting, and under certain circumstances can even increase lean mass while you are losing fat.
Lift First…then…all the other ‘stuff’.
Collateral fattening in body composition autoregulation: It’s determinants
and significance for obesity predisposition
Abdul G. Dulloo, Jennifer L. Miles-Chan, Yves Schutz
European Journal of Clinical Nutrition (2018) 72657-664