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Green tea extracts(GTE) can affect fat loss via short term and long term mechanisms. Factors that influence GTE effects on fat metabolism include bioavailability and individual differences(1). Exercise may also play a role in GTE and fat metabolism. GTE exists as one of four catechins which include EGCG, ECG, EGC and EC. EGCG has been identified as the most pharmacologically active (2).
Short term usage of GTE has been associated with influencing the sympathetic nervous system. COMT, catechol-O-methyltransferase, is found distributed throughout muscle and adipose tissue(3). COMT functions to degrade catechins. EGCG is believed to inhibit the activity of COMT(59). As a result, concentrations of circulatory catecholamines are greater which increases activity of the sympathetic nervous system(4). The enhanced SNS stimulates lipolytic activity and increases fat oxidation.
Long term usage of GTE, has been associated with acting on gene expression. In vivo studies have shown that long term usage reduces adipogenic genes such as lipoprotein lipase and FA synthase (5). Extended usage of GTE has been shown to increase transcription of lipolytic and beta oxidation enzymes in the liver and fat tissue (6,7). Friedrich et al (8) observed that EGCG consumed by mice for four days resulted in lower triglycerides and glycogen levels postprandial. Downregulation of fatty acid synthase accompanied these metabolic changes.
Endurance exercise increases fat oxidation in obese and normal weight populations(3). Murase et al.(9) observed an increase in fat oxidation in adipose metabolism-specific enzyme gene expression for mice given GTE along with exercise than those only prescribed exercise.
Tsai et al (10) performed a randomized controlled study to determine the effectiveness of a green tea meal replacement formula on weight loss. The study included 120 individuals from healthy, overweight and obese populations. The treatment group loss weight and fat mass after the 12 week study. The mean weight loss of the treatment group was 4.0 kg and 6.5 kg at 6 and 12 weeks respectively. The mean weight loss of the control group was 1.9kg and 2.4kg at 6 and 12 weeks respectively. The treatment group also experienced a greater loss in fat mass after 12 weeks than the control group. The fat mass of the treatment group was reduced by 3.9 kg. The control group did not show a significant decrease in fat mass.
Yang et al (11) examined the effects of green tea in combination with inulin on fat mass and body weight in obese and overweight subjects. This six week study demonstrated that the experimental group had a greater loss of body weight and improved BMI measurements. The effects were sustained after 2 weeks of refraining from green tea consumption. BMI and body weight was reduced at the 3 and 6 week marks in the treatment group. The mean BMI of the experimental group initially, at the week 6 mark and week 8 mark was 27.3, 26.6 and 26.7 respectively. The mean BMI for the control for the same time frames was 26.7, 26.7 and 26.8 respectively. The mean weight for the experimental group for the initial, 6 week and and 8 week marks was 76.7kg, 74.7 kg and 74.9 kg respectively. The mean weight loss for the control group for the initial, 6 week and 8 week marks was 73.2kg, 73.1 kg and 73.3 kg respectively.
Dulloo et al (12) concluded that green tea extract increases 24 hr energy expenditure and fat oxidation by 4%. If a person burns 2000 calories per day this would result in an additional 80 calories burned per day. This results in an extra 560 calories burned per week. Depending on body weight and caloric expenditure, my estimate is that anywhere from 0.25 to .50 pounds lost per week is a reasonable expectation.
According to the National Institute of Health (13), there are no reported adverse reactions with the consumption of green tea as a beverage. Consumption of the green tea extract can produce the following side effects: increased blood pressure, nausea, constipation and abdominal discomfort. The ethanolic extract of green tea has been linked to liver damage(13). Iron rich foods are thought to inhibit the antioxidant effects of green tea(13). According to University of Maryland Medical Center(14), people taking blood thinning medications should not consume green tea. According to the American Botanical Council (15), green tea extract is contraindicated for those with anxiety disorders, hyperthyroidism and renal disease. The American Botanical Council recommends eight 250 mg EGCG capsules daily to treat obesity (15).
As long as a patient does not suffer from the contraindications listed above I would recommend this supplement. I would recommend patients replace soda beverages with green tea to decrease daily caloric intake.