Green tea has some interesting properties for those interested in optimum health. Research has shown that regularly consumption of green tea reduces the chance of developing certain types of cancer, particularly of the gut. As well as this green tea consumption has shown protective effects against cardiovascular disease. Green tea contains a number of flavonoid phytonutrients called catechins (flavan-3-ols) that are thought to provide some of its biological activity. The main catechins present in green tea are epigallocatechin gallate (EGCG), epicatechin (EC), epigallocatechin (EGC), and epicatechin gallate (ECG). These catechins are largely destroyed during the fermentation process in the production of black tea. As well as their beneficial effects on heart disease and cancers, green tea catechins also possess some useful properties that suggest that green tea causes weight loss.
In order to determine if green tea causes weight loss, a study published in the Journal of Nutrition in 2009 investigated the ability of catechins to control weight1. The researchers took obese subjects and placed them on an exercise programme for 12 weeks. They gave one group a catechin containing drink, and the other group an identical drink but with no catechins. After the study period was complete, the group who were consuming the catechins had twice the weight loss of the control group. In addition, the group with catechins in their diet had a greater reductions in total abdominal fat area and greater losses of subcutaneous abdominal fat. Similar studies conducted in mice have found that long term consumption of green tea can attenuate the formation of obesity and metabolic syndrome. These results suggest that green tea causes weight loss.
The mechanisms by which green tea causes weight loss appear to be multifactorial. Some research has looked at the ability of green tea catechins to increase energy expenditure. For example, research published in the British Journal of Nutrition in 2005 showed that consumption of a capsule containing caffeine and EGCG three times a day significantly raised twenty-four hour energy expenditure in healthy men2. Another paper published in the American Journal of Clinical Nutrition in 1999 also showed that a green tea extract was also able to increase twenty-four hour energy expenditure in healthy men3. If energy expenditure is increased with catechin consumption it would tend to suggest that green tea has thermogenic properties, that is, it is able to allow and increased production of heat from burning fat.
This fat burning effect is backed up by a study published in in the Journal of Nutrition in 2001. These researchers showed that fat oxidation was 12 % higher in men who consumed catechin containing tea when compared with water4. The authors concluded that the caffeine and catechins, as found in in green tea, have a synergistic effect on fat oxidation. As well as the ability to increase fat oxidation, catechins appear to have the ability to decrease food consumption. Rats fed EGCG consume 15 % less food and lose 5 % of their initial body weight. A study published in the American Journal of Clinical Nutrition in 2006 demonstrated that that green tea consumption with a meal was able to prevent the absorption of up to 25 % of the carbohydrate consumed in the meal in human subjects5. These last two studies indicate that green tea catechins may be effective in reducing energy intake.
So if green tea causes weight loss, what is the best way to incorporate green tea into the diet in order to benefit from this effect? Supplements are available in capsule form which contain green tea. Often these capsules are standardised to provide a certain quantity of one or all of the active catechin ingredients. While many of the studies have used capsules, and I have no doubt they are effective, I do not personally think this is the best way to take green tea. The reason is that capsules are expensive and this tends to limit the amount of green tea that you can consume. I think a better solution is to freely drink the tea, either in bags, or preferably in loose leaf form. A cup of green tea made with loose leaves gives around five to ten grams of green tea, which can equate to as many as 10 to 20 capsules. Drinking the tea is also much cheaper and centuries of consumption by the Japanese and Chinese have proven its safety. If green tea causes weight loss, drinking tea therefore appears to offer the largest chance of success.
RdB
