In people with obesity who lose weight through dieting, losing muscle or other lean tissue does not, by itself, predict whether they will regain weight after one year, once their original...

We analyzed the available evidence and found that losing fat-free mass—like muscle—during dieting does not, by itself, predict whether someone with obesity will regain weight after one year, as long as their original calorie-burning rate is considered [1]. This means that even if a person loses muscle while dieting, their chance of regaining weight isn’t clearly tied to that muscle loss alone. What matters more is how their body’s energy use changes over time, especially if it drops after weight loss. We didn’t find any studies suggesting that muscle loss directly causes weight regain. Instead, the evidence we’ve reviewed leans toward the idea that metabolism—how many calories the body burns at rest—is the stronger factor in whether weight comes back. This doesn’t mean muscle loss is unimportant for health or strength, but when it comes to predicting weight regain after one year, our current analysis suggests it’s not the main driver. What we’ve found so far highlights the need to look beyond just body composition and focus on metabolic adaptation during and after dieting. For someone trying to maintain weight loss, this suggests that preserving muscle may help with overall health, but keeping your metabolism active through movement and protein intake might matter more for long-term results.