Green tea contains higher concentrations of L-theanine and catechins compared to black tea. This may explain its beneficial effects on weight loss.
Green tea causes weight loss, and this may explain the health benefits associated with its consumption. To date, most research investigating the anti-obesity effects of tea has focused on the polyphenol and caffeine content. Both green, black and oolong teas have been reported to have weight loss effects, and this has been largely explained by the caffeine and polyphenols present in tea leaves. Generally the caffeine concentration of green, black and oolong teas is similar, but green tea contains higher concentrations of catechins. Because green tea shows greater anti-obesity effects compared to black tea, it has been suggested that the presence of higher concentrations of catechins may be responsible for these effects. However, green tea also contains higher concentrations of the amino acid L-theanine1, suggesting that the weight loss effects of green tea may be attributable to other components. Synergism between the L-theanine, catechin and caffeine components may also explain why green tea causes weight loss.
Researchers have investigated the anti-obesity effects of the caffeine, catechins and L-theanine components of green tea alone and in combination using animal experiments. In one such study2, researchers fed mice a diet containing 2 % green tea or equivalent diets that contained the same quantity of catechin (0.3%), caffeine (0.05%0 and L-theanine (0.03%) as found in the 2 % green tea diet. The mice were then allowed ad libitum access to food and water. Following 16 weeks on the diet, all mice had gained weight. While the catechin diet showed a trend towards an anti-obesity effect, this effect was not significant. However, the mice fed green tea, caffeine or L-theanine had significantly less body weight gains compared to the control mice. Therefore L-theanine and caffeine may possess the strongest individual anti-obesity effects in green tea. However, green tea is a complex mixture of many components and these may act synergistically to explain why green tea causes weight loss.
Therefore the researchers then assessed the caffeine, L-theanine and catechin in various combinations to assess the synergism between the compounds. Compared to the controls, diets containing caffeine plus L-theanine plus catechin, caffeine plus catechins, and caffeine plus L-theanine all showed anti-obesity effects. However, the catechin plus L-theanine diet showed no significant difference to the control diet. In addition, the caffeine plus catechin plus L-theanine, the caffeine plus theanine and the caffeine plus catechin diets all decreased the concentrations of nonesterified fatty acids (NEFA) in the plasma. The catechin and the catechin plus L-theanine also decreased the triglyceride concentration of the liver significantly compared to the control diet. From these results the authors concluded that L-theanine and caffeine were responsible for the anti-obesity effects of green tea. However, the anti-obesity effect of caffeine was enhanced by the presence of catechins. Therefore green tea causes weight loss because of its caffeine, L-theanine and caffeine content, suggesting that decaffeinated tea may also be beneficial.
