I’m sure you’ve heard of the health benefits of green tea before.
It’s natural, it’s green, it has antioxidants, and some people believe it can help prevent cancer and delay ageing.
Now I don’t know about such strong claims, but tea does actually provide a range of health benefits.
But I’m really not going to get into that here.
I’m going to explore how green tea affects your metabolism, and why it has started popping up in the majority of fat loss supplements on the market.
If you look at the ingredients list for a popular fat loss supplement then chances are you will see green tea extract on there.
Compounds in Green Tea
Green tea contains certain active compounds, notably Caffeine and its relatives Theophylline and Theobromine (in small amounts). Caffeine is a well known stimulant, but Theophylline and Theobromine also provide a small effect.
Additionally, Green Tea contains an amino acid known as L-Theanine, which does have a sedative effect that is believed to oppose some of the stimulant effects of Caffeine.
Catechins are another class of compounds that Green Tea contains in abundance, and these are believed to be part of the reason for its health benefits.
The biggest source of these is EGCG (Epigallocatechin Gallate), one of the active compounds in green tea, and likely one of those that can raise metabolism.
Does Green Tea Increase Your Metabolism?
Two placebo-controlled cross-over studies were performed, one with 12 healthy men and the other with 11. They exercised at a moderate intensity, while taking either green tea extract or placebo, and several markers were measured.
The results were that their levels of fat oxidation were 17% higher, and the contribution of carbohydrate to energy expenditure was correspondingly reduced. Their insulin levels were also reduced. This study suggests that green tea extract increases fat oxidation during exercise (1).
A study with 10 healthy men found that green tea extract increased 24 hour energy expenditure by 4%, with the same amount of isolated caffeine showing no effect. This suggests that green tea may increase the metabolic rate, more than can be explained simply by the caffeine content (2).
In one study, 60 obese individuals from Thailand were randomized to either a green tea extract group or a placebo group during a 12 week calorie controlled weight loss period. The group taking green tea extract lost significantly more weight (3).
A trial with 132 obese individuals found that green tea extract didn’t change total fat mass compared to caffeine, but found that green tea caused a significantly greater fat loss in the abdominal area (4).
My take on these studies is that green tea may cause a modest, temporary increase in the metabolic rate and may slightly increase fat oxidation.
The mechanism suggested is that the catechins in green tea partially inhibit an enzyme that breaks down the neurotransmitter Noradrenaline (usually stimulating), effectively increasing its effects and contributing to increased fat burning.
Personally, I think that green tea may provide a modest weight loss benefit, but its effects are so minor that they are dwarfed by any possible effect caused by a healthy diet and exercise program.
But for those who are already doing all the right things and need a small push, green tea may give a tiny boost in the right direction.