Does caffeine increase fat metabolism? Original paper

In this meta-analysis of randomized controlled trials, ingesting caffeine increased fat metabolism to a small-to-moderate extent. Surprisingly, this effect was independent of dosage.

The effect of caffeine ingestion on fat metabolism, including fat oxidation.

984 young adults (average age of 26; 84% men, 16% women).

The researchers conducted a systematic review and meta-analysis of 94 randomized controlled trials. The dose of caffeine varied widely among the studies (1–15 mg of caffeine per kilogram of body weight). Most of the studies (63%) tested the effects of caffeine on fat metabolism in fasted participants (≥3 hours from their last meal).

The included studies examined the effects of caffeine on fat metabolism via expired gas analysis and blood biomarkers (e.g., free fatty acids and glycerol levels).

Moreover, the researchers performed subgroup analyses to judge whether sex, fitness level, or caffeine dosage influenced the outcomes.

Ingesting caffeine acutely increased fat metabolism by a small-to-moderate effect size.

Across all of the studies, the beneficial effects of caffeine on fat metabolism were greater in the participants at rest compared with the participants who were examined during exercise. However, this effect was not present in studies that compared the two conditions directly.

Sex, fitness level, and caffeine dosage did not influence caffeine’s effect on fat metabolism.

It’s surprising that caffeine’s effect on fat oxidation was independent of the dose, given that the ergogenic (i.e., performance-enhancing) effect of caffeine can be modulated by the dose. One possible explanation is that the ergogenic effects of caffeine are not tied to its beneficial effects on fat metabolism.