We analyzed one assertion on this topic and found that overweight and obese young men who did aerobic exercise while fasted for six weeks showed lower fasting insulin levels compared to those who did the same exercise without fasting [1]. The evidence we’ve reviewed so far leans toward this outcome, with no studies in our current set contradicting it. Fasting insulin is a measure of how much insulin is in the blood after not eating for several hours — it can give a sense of how well the body manages blood sugar. Lower levels may suggest improved insulin sensitivity, meaning the body needs less insulin to keep blood sugar in check. We did not find any data showing that fasted exercise raised insulin levels or had no effect. However, this conclusion is based on a single assertion, and we have no details about the study design, sample size, or how insulin was measured. There’s also no information on whether these changes lasted beyond six weeks or if they translated to other health outcomes like weight loss or reduced fat. Because our analysis includes only one assertion, we cannot say whether this pattern holds across different populations, exercise types, or durations. We also don’t know if the fasting period was overnight, or how long before exercise the fast began. More studies would help clarify whether this effect is consistent, how strong it is, and who might benefit most. For now, if you’re an overweight or obese young man considering fasted aerobic exercise, this one piece of evidence suggests it might help lower fasting insulin levels — but it’s too early to say whether it’s better than exercising after eating. What we’ve found so far is limited, and more research is needed.