Berube-Patent, S., Pelletier, C., Core, J., & Tremblay, A. (2005). Effects of encapsulated green tea and Guarana extracts containing a mixture of epigallocatechin-3-gallate and caffeine on 24h energy expenditure and fat oxidation in men. British Journal of Nutrition, 94, 432-436.
This study is listed on the Hydroxycut website as supporting evidence that their product works, due to two of its key ingredients: 1) Guarana, which contains caffeine and 2) Green Tea, which contains epigallocatechin-3-gallate (EGCG), and caffeine. Green tea contains catechins which have antioxidant properties, such as aiding in the fight against cardiovascular disease, some cancers, and most recently obesity; EGCG is the most abundant catechin in green tea. In addition, 3-5% of Green Tea’s dry weight is caffeine.
Right away being on their website, I wonder what came first: the money to support the study via Hydroxcut’s company, or the study that happens to support the product. Either way, the study seems legitimate. The main research question was: What is the best combination of caffeine and EGCG to produce a significant increase in energy expenditure and fat oxidation without producing negative cardio-stimulatory side effects (increases in blood pressure and heart rate).
Details of study design and specific outcomes can be found in the paper, however generally the 14 male subjects sent 5 separate 24 hour occasions in a metabolic chamber in order to determine the effects of various mixtures of caffeine and EGCG. The EGCG content was determined by using 45% the dry weight of Green Tea, while the caffeine content was determined from Guarana. This is a limitation to the study design considering that both Green Tea and Guarana had other unknowns in them, including additions catechins and caffeine. Three measured values were determined to be significantly different: 24 hour energy expenditure, 24 hour diastolic blood pressure, and carbohydrate oxidation. 24 hour energy expenditure was significantly different that the placebo, proving that these ingredient can aid in weight loss.
In addition, key findings were that beyond a certain threshold, the EGCG content of a compound only produces a small, non-significant additional increase in 24 hour energy expenditure, so it in not clinically beneficial to increase the EGCG content at the expense of also increasing the negative cardio-stimulatory effects. Negative cardio-stimulatory side effects include an increase in heart rate and blood pressure, two things regular exercise has been shown to reduce; therefore exercise, in addition to the supplement, will help fight the negative side effects. Next, a known effect of weight loss is a decrease in resting energy expenditure (RMR), another benefit of EGCG-caffeine mixtures is that it may keep the RMR elevated (how much as weight loss increases needs to be determined). Finally, it was concluded that EGCG-caffeine mixtures have a place in weight loss interventions, along with diet and exercise, not in place of.