How does a 4.5mg/kg dose of caffeine sound for boosting metabolism and associated fat burning? Pretty high most would say. Well that’s the only dose that was found to have a significant effect on energy expenditure compared with doses of 0.5, 1.5 and 3.0mg in a recent study from the University of Castilla-La Mancha in Spain. In this study, 12 physically fit males were made to cycle for 1 hour after ingesting one of the caffeine doses outlined above. The study was placebo-controlled such that each participant repeated the test on 5 different occasions; each time with a different dose of caffeine as well as a placebo. The following three hours after each session, the subjects had their heart rate, blood pressure, ventilation, tidal volume, glucose, lactate and fatty acids monitored. None of these measures showed any significant difference with the exception of when subjects took the 4.5mg dose. On such occasions, ventilation and tidal volume were significantly elevated, which correlated with an increase in energy expenditure. The premise of the study centred on the fact that caffeine has a long half-life and therefore its effect could remain even after exercise. However, it seems one needs to take a pretty hefty dose (i.e. 337mg for a 75kg individual) to see lasting effects on metabolism and energy expenditure.
Fernández-Elías VE, et al. Ingestion of a Moderately-High Caffeine Dose Before Exercise Increases Post-Exercise Energy Expenditure. Int J Sport Nutr Exerc Metab. 2014 Jun 5. [Epub ahead of print]