In young lean men, those with higher levels of a specific muscle enzyme involved in energy production tend to gain less body fat when consuming excess calories over time.

We analyzed the available evidence and found that in young lean men, higher levels of a specific muscle enzyme involved in energy production are linked to less fat gain during periods of overeating [1]. This enzyme helps muscles use energy more efficiently, and the data suggest that individuals with more of it may be better at burning off extra calories before they turn into stored fat. What we’ve found so far is based on one assertion, supported by 38.0 data points, with no studies or observations contradicting it. While this pattern is consistent, it comes from a narrow group—only young, lean men—and we don’t yet know if the same holds for women, older adults, or people with different body compositions. The evidence we’ve reviewed leans toward a connection between higher muscle oxidative enzyme activity and reduced fat gain during overfeeding, but we can’t say this applies broadly or why it happens. It’s possible that people with more of this enzyme naturally process excess energy in their muscles rather than storing it as fat, but we don’t have enough information to confirm the mechanism. We also don’t know if this enzyme level can be changed through training, diet, or other habits. For now, the pattern is clear in the data we’ve seen, but it’s limited in scope. If you’re someone who gains fat easily during overeating, this doesn’t mean your metabolism is broken—it may just reflect differences in how your muscles handle energy. More research is needed to understand if this enzyme plays a role in other groups, and whether it can be influenced.