Study shows that caffeine increases fat burning, but does it matter?

In a new Spanish study that was published in the European Journal of Nutrition the role of caffeine in fat burning (oxidation) was investigated (1). The idea that caffeine stimulates fat oxidation dates back to the 1970s, but studies have produced very mixed results. The new study from Juan del Coso’s research group (a very well conducted study), showed improvements in fat oxidation by 27%. But does this matter? Is it important?

Greater fat mobilisation with caffeine

The studies by David Costill in the late 1970s (2) showed that caffeine can increase the mobilisation of fatty acids from their stores. Fat is stored in several tissues but mostly in adipose tissues. The fatty acids are released from adipose tissue, can be transported to the muscle and be used as fuel. Some, but not all, studies show also an increase in fat oxidation with this elevation in fatty acids. However, it is not always true that an elevation in fatty acids levels in the blood also results in increased fat oxidation. This increase in fat oxidation was originally used to explain the performance benefits but it is now generally accepted that the increase in fat oxidation, does not spare muscle glycogen and improve performance. The performance enhancing effects of caffeine are predominantly through effects on the central nervous system.

New study finds increased fat oxidation with caffeine

The authors conducted a placebo controlled double blind study. Participants conducted two experimental trials. Before one of these they ingested 3 mg/kg of caffeine and before the other trial they ingested the same amount of a placebo. The capsules were ingested 1 hour before exercise. The participants (12 in total) exercised at fatmax intensity. This means that in an earlier test, the researchers had established the exercise intensity where these participants oxidised most fat. This is highly individual but on average was around 50% VO2max, a low-to-moderate exercise intensity.

During the hour of cycling, the subjects oxygen uptake and carbon dioxide production were measured and fat and carbohydrate oxidation were calculated from this. What the researchers found was an average total fat oxidation of 19.4 grams for the hour with placebo and 24.7 grams with caffeine. That is a whopping 27% more fat oxidation. They also found that there was no difference in energy expenditure and thus the increased fat oxidation meant that carbohydrate use was used (or carbohydrate was spared).

The researchers found an average total fat oxidation of 19.4 grams for the hour with placebo and 24.7 grams with caffeine. That is a whopping 27% more fat oxidation with caffeine.

Questions raised

The findings raise two questions. How does this relate to the rest of the literature, because we don’t want to make the mistake of drawing a conclusion on the basis of a single published study. The second question is what are the practical implications, if any?

The finding that caffeine can increase fat oxidation is not new. Several studies have shown this before, but it is important to realise that there are also many studies that did not see any effect of caffeine on fat oxidation. The different findings can at least party be explained by the exercise intensity used in the studies. A previous study by Juan del Coso's research team (2) showed that effects of caffeine on fat oxidation could be observed at lower intensities but not at higher intensities (>80%VO2max).

There are other factors that could affect the outcomes as well, such as how trained the tested individuals were, the duration of the activity, the control of the diet before the trials and so on. But overall the findings of the study are in line with several previous studies and I would conclude that caffeine CAN in some situations increase fat oxidation. I was maybe a little surprised by the magnitude of change in this study, which seems a little greater than other studies. Of course, the effects may have been exaggerated by the fact that these studies were conducted in the fasted sta