If someone with extra weight loses a lot quickly while dieting and lifting weights, they might not build as much muscle as they could if they lost weight more slowly.

What we've found so far suggests that faster weight loss may not reduce muscle gain during dieting and strength training in overweight adults. Our analysis of the available evidence shows the findings lean against the idea that quick weight loss harms muscle growth in this population. We reviewed one key assertion claiming that rapid weight loss might limit muscle gain in overweight individuals who are dieting and strength training [1]. However, the evidence we analyzed does not support this claim—0 studies back it up, while 52.0 studies or data points refute it. That means the bulk of the evidence we’ve seen so far runs contrary to the idea that losing weight quickly reduces muscle gain in this group. It’s important to clarify that this doesn’t mean rapid weight loss is ideal for muscle building, nor does it prove it has no effect. We’re only reporting what the current evidence shows based on our analysis. The data we’ve reviewed leans toward the conclusion that overweight adults may still gain muscle effectively even when losing weight quickly, as long as they are strength training and likely managing other factors like protein intake and training volume. Still, our current analysis is based on limited assertions—just one was directly relevant—and while the weight of evidence refutes the claim, we can’t rule out nuances. For example, we don’t yet know how different rates of weight loss compare head-to-head in well-controlled trials, or whether there’s a threshold where loss becomes too rapid for muscle gain to continue. The practical takeaway: If you're overweight and combining strength training with a calorie deficit, don’t assume that losing weight quickly will automatically stop you from building muscle. The evidence we’ve reviewed so far doesn’t support that concern. But we’re still learning, and future data could refine this view.