Safe, natural, and effective, green tea extract is one of those ingredients that pops up in a lot of supplements, most notably fat metabolisers.
The major active chemicals in green tea are known as catechins. Catechins are thermogenic compounds, which are thought to speed up the metabolism and increase the rate of fatty acid oxidation. On top of this, green tea extract has strong antioxidant properties, and many extracts contain significant amounts of caffeine and its derivatives. Green tea has also been investigated for its positive effect on cardiovascular health, anti-inflammatory properties, and even for its effects against cancer cells.
Along with fat burning, green tea is often said to enhance performance, and features in a number of pre-workout formulations. While it is thought that the fat-burning properties of green tea extract are amplified by exercise, There is a lot less research that looks into whether or not green tea enhances performance, and if so, how this occurs.
A group of researchers in Canada decided to tackle these questions, and set up a small trial to look at the short term effects of green tea extract on various aspects of metabolism and athletic performance.
Fifteen young, active men were recruited for this double-blind study, and for two days received either 1000mg per day green tea extract, or a placebo. On the third day, the men ate breakfast before performing a cycling exercise designed to stimulate fat burning, and then a time trial. Various metabolic parameters were measured before and during the exercise. After a one week wash out period, the men repeated the exercise with the other treatment.
The results confirmed what has been seen before, with higher venous blood levels of glycerol both at rest and during exercise in the green tea group confirming that those people on the supplement had burned more fat. A lower average heart rate was also observed in this group during exercise, but surprisingly, no other metabolic differences were observed between groups. This included insulin levels, levels of free fatty acid, blood glucose and notably, resting energy expenditure. On top of this, the results in the time trial did not show significant differences between the two groups.
This study was an interesting first look at the effects of green tea on exercise performance. The effect on heart rate is particularly notworthy, and it's clear that this is something that needs to be explored in greater detail. The researchers have also confirmed something that many people already knew – that green tea extract really does increase fat loss. Add that to green tea's all round health benefits, and it's probably time for a cuppa.
Martin BJ, Tan RB, Gillen JB, Percival ME, Gibala MJ. No Effect of Short-Term Green Tea Extract Supplementation on Metabolism at Rest or During Exercise in the Fed-State. Int J Sport Nutr Exerc Metab. 2014 Jun 5.