Fasted cardio: the truth about its 'fat-burning' effect
The fasted-cardio idea is built on a real fact: without carbs in your bloodstream, your body does switch faster to using fatty acids as fuel during that specific session. That part is true — but it's only part of the picture, and it's misleading on its own.
What matters isn't the fat 'burned' during that one hour, but your total energy balance over 24 hours. Studies comparing fasted vs. fed training at equal weekly calorie totals mostly find no meaningful difference in fat loss after several weeks. The extra fat burned in the moment gets offset by how the body allocates energy differently for the rest of the day after eating.
There's also a downside: training on an empty stomach lowers intensity, especially for strength work — you simply have less in the tank for your working weights. So fasted training is more a matter of personal comfort and tolerance than a scientifically proven edge for fat loss.