Green tea is a popular supplement in the diet industry. This popularity relates to evidence that shows that green tea consumption may induce weight loss. The exact reason for the weight loss effects of green tea are not known, but a number of mechanisms may explain the fat loss effects observed. Firstly, green tea is a source of caffeine, and caffeine like all dietary methylxanthines is able to stimulate the sympathetic nervous system, and in the process this may raise metabolic rate and induce fat loss. Alternatively, an amino acid in green tea, l-theanine, may have fat loss effects, although they are not as well described, and possibly not as significant as those of caffeine. Lastly, green tera is a source of polyphenols called catechins (also called flavan-3-ols) and these may also have the ability to increase fat oxidation. Studies on mice suggests that the caffeine, l-theanine and catechins may act synergistically in their fat oxidation effects, although this may not been convincingly demonstrated in humans.
Green tea is a good source of a group of polyphenols called catechins. These catechins may have general health effects because of their antioxidant capacity. They may also help to induce fat loss. Catechins may interact with the hydroxypropyl methylcellulose, of which some capsules are made, and this may alter their absorption kinetics. Comparisons of gelatin and hydroxypropyl methylcellulose, the latter appears to alter absorption kinetics of green tea catechins. Drinking green tea, or obtaining the catechins from gelatin capsules may therefore be the better option.
The catechins in green tea have also been shown to have antioxidant effects, and may therefore be useful for improving general health. Drinking green tea provides several hundred milligrams of catechins, and this is the prefered way in which to obtain these polyphenols. Some do not like the bitter taste of green tea and so choose to consume the tea in capsule form. However, some evidence suggests that capsules may inhibit the absorption of catechins from green tea because the catechins and the hydroxypropyl methylcellulose (HPMC), of which some capsules are made, may interact. Additionally, the dissolution rate of capsules and their cellulose fillers may further inhibit the absorption rate, or at least alter the absorption kinetics, of the green tea catechins. This has been suggested to account for the lack of effects of green tea capsules in some studies. Gelatin capsules, tablets or drinking green tea may therefore be the prefered method of consuming green tea in order to maximise catechin absorption.
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