Green tea and green tea supplements are frequently marketed as a way to boost metabolism; and some people are buying into this idea by purchasing green tea extract supplements as a way to lose weight. Others are drinking large quantities of green tea in hopes of seeing those extra pounds melt away. Is there any real truth to the claims about drinking green tea and weight loss?
Most of the studies that have looked at drinking green tea and weight loss have been done in animal models which may not always mirror the results seen in humans. Even the effects seen in animals can vary depending upon the species, making it hard to extrapolate from animal to human. There are a variety of animal studies showing that the catechins found in green tea, particularly EGCG, can promote weight loss. In addition, green tea catechins have been shown to have positive effects on blood sugar and cholesterol levels in animals.
What about human studies looking at drinking green tea and weight loss? Several small human studies have shown that use of a green tea extract can boost metabolism by up to four percent. The EGCG found in green tea has been shown to inhibit an enzyme called fatty acid synthase which is associated with fat synthesis and storage. This may play some role in its ability to promote fat loss. Although it may be tempting to attribute some of the weight loss effects to caffeine, the metabolism boosting effect was greater when green tea was given compared to caffeine alone.
A recent human study published in the Journal of Nutrition showed that green tea catechins boosted the amount of weight and abdominal fat loss subjects experienced as part of a moderate intensity exercise program. Those who were supplemented with a catechin containing beverage while on the program experienced more weight and abdominal fat loss than those who received a beverage with caffeine but no catechins. This suggests that the effect of drinking green tea on weight loss isn’t solely due to the caffeine.
Although the effects of drinking green tea and weight loss look promising, human studies have been limited and small in size making it difficult to draw conclusions. Even if drinking green tea does boost metabolism, the effects appear to be modest. Using green tea for weight loss would likely have the greatest benefit when used in conjunction with a regular, vigorous exercise program. Unfortunately, there’s still no substitute for the old standbys, healthy eating and exercise.