“Fasted cardio burns more fat.”
Moderate confidence. Fasted aerobic exercise often increases the proportion of fat oxidized during that session, but controlled training studies have not shown a clear advantage for total body-fat loss. Most longer-term studies are small and short.
There is a short-term effect, but it is commonly misinterpreted. Fasted cardio can use more fat as fuel during the workout. That does not automatically produce more body-fat loss over time when total food intake and training are similar.
Fat loss depends on energy balance across days and weeks, not just which fuel supplied one workout. Eating first may also support higher training quality or longer duration for some people.
Safety note: Fasted exercise can increase lightheadedness or low-glucose risk in susceptible people. Risk depends on exercise duration and intensity, diabetes medicines, pregnancy, illness and eating-disorder history.
Talk to a healthcare professional if: Get individualized advice before fasted exercise if you use insulin or glucose-lowering medicine, are pregnant, have recurrent fainting or hypoglycemia, or have an active or past eating disorder.
Fasted cardio is optional. Use it if it is convenient and you feel and perform well. Eating before exercise is also compatible with fat loss.
Choose the fed or fasted approach that helps you train consistently without dizziness, unusual fatigue or rebound overeating. Do not treat fasted training as a requirement for fat loss.