Green Tea: Does it deserve the hype?
A little background
Tea is the most widely consumed beverage in the world next to water, with the awareness of the extensive benefits of tea existing for centuries by Asian communities. Green tea fermentation is inhibited through rapid steaming of the leaves, with the final product containing naturally occurring flavonoids and caffeine. Through the manufacturing process of no fermentation, green tea preserves high quantities of a sub-group of flavonoids: the catechin polyphenols. Epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC) are the main polyphenols accountable for other beneficial effects such as the antioxidant and anti-mutagenic potential. EGCG is the most abundant and is thought to be the most pharmacologically active catechin. A typical average cup of green tea contains between 100-300 mg of total catechins, and 50-90mg of caffeine. It is the Green Tea Extract (GTE) that is taken from the leaves and manufactured into various forms such as capsules, or powdered supplements along with other ‘fat burning’ ingredients.
Does it actually aid in fat burning?
A few studies have looked into the varied levels of catechins within green tea and how they effect long term fat reduction. In a 12 week study, one set of testing subjects where provided with a green tea beverage containing 583mg of catechins to consume everyday, along with a control group of only 96mg of catechins to consume everyday (similar to a standard cup of green tea). This study found a greater decreases in body weight, fat mass, visceral fat and subcutaneous fat seen in the high catechin group compared with the low catechin group. These results are even more interesting due to the fact that the caffeine content in both trial groups were very similar. This is also backed by another study that has shown that 24 hour energy expenditure increases further when green tea extract is added to caffeine. This helps draw the conclusion that the fat reduction effects derive from the high levels of catechins within the testing drinks.
In other studies however, it was found that individuals of Asian populations found greater weight loss over a 12 week period (1.51kg) compared to that of Caucasian populations (0.82 kg). It is therefore postulated that these result occurred due to a higher habitual caffeine intake for the Caucasians compared with the Asian populations, potentially caused a possible decrease in sensitivity to the effects of caffeine and catechins through high levels of consumption.
In more acute cases fat oxidation rates (fat burning) during exercise have also found positive effects through GTE administration. In one study, fat oxidation rates during moderate intensity exercise after ingestion of GTE (with no caffeine) in healthy young men. It was found that the ingestion of GTE increased whole-body fat oxidation significantly more than that of a placebo trial, again supporting the fact that GTE effects work independently of caffeine.
It has also been observed that GTE significantly reduced insulin concentrations (hormone responsible for regulating blood sugars) following an oral glucose tolerance test. This data is significantly important as insulin is by far the most potent inhibitor of lipolysis (fat breakdown) with even a slight increase in plasma insulin supressing the lipolytic rate by more than 50% below baseline levels.
So how does it work?
It has been known for years that caffeine can increase the fat oxidation process. So without getting too complex here is how I does so. Caffeine stimulates the sympathetic nervous system (SNS) resulting in a rise to the circulating catecholamines: epinephrine (adrenalin) and norepinephrine. These hormones, secreted by the adrenal gland, are the primary mediators of adipocyte (fat cell) lipolysis (fat breakdown) via beta adrenergic receptor stimulation. This results in more fat being available in the blood to be used as energy in the working muscles.
Another proposed mechanism from the catechins in green tea is through enzyme inhibition of Catechol-O-methyltransferase (COMT). COMT is an intracellular enzyme that has been shown to degrade catechol compounds. GTE ingestion has been exposed to directly inhibit COMT through the resulting high concentrations of EGCG (Goldstein, Eisenhofer, & Kopin, 2003). There is also is a difference in responses to certain populations that may also be due to the wide variability in the activity of COMT, which has shown to vary as much as three fold between individuals and populations.
These synergistic actions of both caffeine and EGCG are suggested to result in the increase rates of fat oxidation following GTE ingestion. The main body of literature suggests that GTE + caffeine can stimulate amplified fat oxidation and reduce body fat over time. However there is shown disparities to these effects depending on habitual caffeine consumption, race or the amounts and distribution of GTE + caffeine mixtures. The high individuality of response and some contradictory research suggest that GTE as an ergogenic aid may not work for everyone looking to reduce body fat.