Drinking green tea offers many health benefits, including cancer prevention and decreasing the risk of developing cardiovascular disease. There is another important benefit of green tea. In some research studies, green tea extract alters body composition by increasing metabolism, thus aiding in weight reduction. However, this is not conclusive because not all studies show this benefit.
Active Compound in Green Tea
The tea plant is naturally high in a group of antioxidants known as catechins. Green tea offers more catechins than black tea because its production involves less processing and fermentation. Catechins are found in green tea (1 cup offers 142 mg), chocolate (4 oz offers 53 mg) and black tea (1 cup black tea contains 27 mg). Catechins may aid weight loss in two ways. They inhibit the breakdown of fats, and they inhibit the production of an inflammatory agent in the body that triggers hunger.
Green Tea Extract for Weight Loss?
GreenSelect Phytosome is a recently developed green tea extract oral supplement (GTE). It was tested in a study published in Alternative Medicine Reviews. One hundred obese men and women were put on a reduced-calorie diet. Half of the participants took the GTE supplement and consumed a reduced-calorie diet, and the other half followed only the diet. After 90 days, significant weight loss and a decreased body mass index (BMI) were observed in the group taking the GTE supplement (a 14-kg loss in the treated group compared with a 5-kg loss in the diet-only group). Waist circumference was reduced only in male participants.
Catechins and Fat Oxidation
A study published by the American Journal of Clinical Nutrition investigated whether the green tea extract (containing caffeine and the catechin known as epigallocatechin gallate, or EG), could increase energy expenditure (EE) and fat oxidation (burning of fat) over 24 hours in humans. On three separate occasions, ten healthy men were randomly assigned to receive one of the following at breakfast, lunch and dinner: green tea extract (50 mg of caffeine and 90 mg of EG), caffeine (50 mg) and a placebo. This study concluded that green tea promotes fat oxidation beyond that which could be explained by the caffeine content.
Does Physical Activity Enhance the Effectiveness?
Another study published in the American Journal of Clinical Nutrition investigated the effects of acute GTE ingestion on glucose tolerance and fat oxidation while participants performed moderately intense exercise. Twelve healthy men engaged in 30 minutes of cycling before and after taking GTE supplements. In the second phase, the same men took an oral glucose tolerance test before and after supplementation. The supplement(s) consisted of three capsules containing either GTE (366 +/- 5 mg EG) or a placebo made of corn flour.
On average, fat oxidation rates were 17 percent higher in the GTE group. The exercise enhances insulin sensitivity in both groups, but the GTE group had a 13 percent greater increase in insulin sensitivity, meaning those individuals would have better blood sugar control.
Significance
Green tea seems to be a low-risk complementary therapy for many conditions, and the evidence and findings from these scientific studies appear to be quite convincing in relation to weight and fat oxidation, particularly in the presence of moderate physical activity.
Drinking just three glasses of green tea daily may contribute to a reduction in body weight and waist circumference (women with a waist of greater than 35 inches and men with a waist of greater than 40 inches are at a much greater risk of cardiovascular disease than their slimmer counterparts) by almost 5 percent in three months. More research is needed to draw conclusions that would lead to specific recommendations.
References
- American Family Physician: Green Tea: Potential Health Benefits; C Schneider and T Segre; 2009
- Alternative Medicine Reviews: Greenselect Phytosome as an Adjunct to a Low-Calorie Diet for Treatment of Obesity: A Clinical Trial; F Di Pierro, et al; 2009
- American Journal of Clinical Nutrition: Green Tea Extract Ingestion, Fat Oxidation, and Glucose Tolerance in Healthy Humans; MC Venables et al; 2008
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