Supplementation with caffeine increased fat oxidation during fed-state aerobic exercise to a moderate degree.

Subgroup analyses:

Caffeine dose: Supplementation with caffeine increased fat oxidation in the trials that administered less than 6 mg/kg of body weight, but not in the trials that administered 6 mg/kg or more. However, the lack of a statistically significant effect in the latter subgroup may have been due to the inclusion of one outlier trial.^[1]
Training status: Supplementing with caffeine increased fat oxidation in the trials that recruited physically active participants, but not in the trials that recruited trained athletes/untrained participants. Again, the lack of a statistically significant effect in the trained athletes/untrained participants may have been due to the inclusion of the aforementioned outlier trial.^[1]
Habitable use of caffeine: Supplementation with caffeine increased fat oxidation in the trials that recruited noncaffeine users, but not in the trials that recruited habitual caffeine users. However, only 3 trials were included in the latter subgroup.

All of the trials included in the meta-analysis were of fair or high methodological quality.

Caffeine increases fat oxidation during fed-state aerobic exercise Original paper