Epidemiological evidence suggests that those who consume relatively large amounts of tea are protected from a number of diseases. This disease protection may relate to the observed fat loss effects of tea, as weight gain increases the risk of many diseases. The fat loss effects of tea were originally suggested to be due to the methylxanthine content of the decoction, as caffeine and other methylxanthines are known central nervous system stimulants. However, more recent evidence suggests that green tea possess significant fat loss effects that cannot be ascribed solely to the methylxanthine component of the plant. Experiments involving animals and humans have identified the flavan-3-ols, also called catechins, as being responsible for some of the fat loss effects of green tea. Flavan-3-ols belong to the group of phytochemicals called flavonoids, and a number of health effects have been suggested to result from consumption of these chemicals. In particular the flavan-3-ol epigallocatechin gallate may have fat loss effects.
A number of studies have tested the effects of green tea on weight loss in overweight subjects. Many such studies have been randomised controlled trials with human subjects. For example, in one such study1, researchers randomly assigned overweight subjects with body mass indices over 25 kg/m2 to receive a diet of 2000 kcals per day supplemented with either green tea capsules containing equivalent of 100 mg per day of epigallocatechin gallate or a placebo capsule. The diet comprised of 65 % carbohydrate, 15 % protein and 30 % fat, and the subjects followed this protocol for 12 weeks during which time their body composition was monitored. By week 8 of the study, the green tea capsule group had lost 5.5 kg more weight than the placebo group and this difference remained until week 12 of the study when the green tea group had lost 3.3 kg more weight than the placebo group.Therefore green tea capsule containing 100 mg per day epigallocatechin gallate show beneficial weight loss effects in overweight individuals.
At week 8, the difference in energy expenditure of the two groups was 48.3 kcals per day with the green tea group having the highest energy expenditure. Therefore the lost weight may be explained by an increase in the energy expenditure of the green tea group. The green tea capsules did contain caffeine, and this was not controlled for in the placebo group, and so it could have been the presence of the caffeine that raised the metabolic rate and increased energy expenditure. However, the flavan-3-ol component of green tea may also increase the metabolic rate and increase energy expenditure, so there may have been some synergism between the two compounds. In fact, weight loss synergism has been shown between caffeine, catechins and another compound in tea leaves called L-theanine, although these effects were observed in rodents. However, irrespective of the causative agent, green tea capsule containing 100 mg of epigallocatechin gallate may possess beneficial weight loss effects.
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