Aaron Deere is a sports nutritionist, functional medicine consultant and advanced personal trainer. He is based in London.
Green tea is made from the leaves of the Camellia sinensis plant that has undergone minimal oxidation during the process of conversion into dried for brewing. It has always been popular in China since ancient times and plays an important role in Chinese herbology.
While black tea still dominates consumption in the western world, green tea popularity is on the rise, not least because it contains a variety of enzymes, amino acids, carbohydrates, lipids, sterols, phytochemicals and dietary minerals, which has seen it hailed as a health food for its perceived ability to increase rates of lipolysis – the process of converting into free fatty acids for fuel – and for its anti-oxidant properties. But does the science back up these claims?
Green tea and fat-burning
Green tea is produced from non-fermented or non-oxidized tea leaves and contains high amounts of catechin polyphenols and caffeine. Catechins are capable of inhibiting catechol-O-methyltransferase, an enzyme that degrades catecholamines, such as dopamine, adrenaline and noradrenaline, and prolongs the stimulation of thermogenesis, which is the heat production process in organisms.
Multiple reviews have been undertaken on the general effects of green tea, arriving at the conclusion that the combined effects of catechins and caffeine have thermogenic properties that promote fat oxidation at levels greater than caffeine alone. Multiple meta-analyses on the general effects of green tea in the general population concluded that: catechin-caffeine mixtures increased fat oxidation and energy expenditure by 4.7%; the effects were seen with catechin-caffeine mixtures between 8.6g to 15.7g/day; catechin-caffeine mixtures are associated with reductions in BMI and body weight; and that increased effects were seen in lower habitual caffeine consumers.
Green tea and exercise
Very little research has been done on the effect of green tea on fat oxidation rates during exercise. One study initially showed a 17% increase in fat oxidation rates with short term supplementation, although subsequent research reported equivocal results with no effects seen on whole body fat oxidation levels in green tea and decaffeinated green tea supplementation groups. The evidence therefore suggests that green tea supplementation at a sufficient dose has an effect on fat oxidation rates at rest, but similar effects have not been reported during exercise.
Green tea and antioxidants
Green tea has been suggested to provide protection against chronic diseases, including cancer. Green tea polyphenols are believed to be responsible for this cancer preventive effect, with the antioxidant activity of the green tea polyphenols implicated as the potential mechanism.
The polyphenols act as direct antioxidants by scavenging reactive oxygen. They may also act indirectly by up-regulating phase II antioxidant enzymes, such as glutathione-S-transferase (GST) and superoxide dismutase.
Green tea supplementation has shown interesting results when directly correlated to exercise and has been shown to give a protective effect against oxidative damage induced by both short-term muscular endurance tests and long-term strength training, resulting in a reduction of anecdotal markers, such as DOMS and time of recovery.
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