Green Tea Extract
What is Green Tea Extract? Green tea is known to contain a high number of active substances that are beneficial to health. It is a particularly good source of flavonoids (Stagg and Millin, 1975), one of these – a catechin (a type of polyphenol) called epigallocatechin allate (EGCG) – has attracted the most attention, from a health perspective. However, the levels of EGCG found in a cup of green tea are low and you would need to consume around 8 cups a day to see a benefit. Green tea extract contains far higher levels of the polyphenols and has been demonstrated in research to have many positive health benefits.
Who might benefit from Green Tea Extract? Anyone looking to loose weight, by increasing the rate of thermogenesis (fat burning), or who is looking for a supplement for general health reasons may benefit from green tea extract.
What does research say about Green Tea Extract supplementation? Research has demonstrated that green tea extract can accelerate the fat burning process (Dulloo, 1996). In fact, the consumption of green tea extract increased the fat burning process in humans by 35-43% (Dulloo, 2000). The subjects in this study had a significant (4%) increase in their daily expenditure. Any, increase in energy expenditure, is likely to lead to a reduction in bodyweight and further research has supported green tea extracts ability to reduce bodyweight (Chantre and Lairon, 2002). It is believed that green tea has this effect by either increasing the amount of norepinehrine (noradrenalin), or prolonging the effects of norepinephrine on thermogenesis. It does this by inhibiting a key enzyme – catechol O-methyltransferase (COMT) – which would normally breakdown norepinephrine (Borchardt et al., 1975).
Another benefit of green tea is a lowering effect on the bad blood cholesterol (LDL) and a raising of good cholesterol (HDL). The exciting thing about green tea extract is that although it raises the metabolic rate, it does not cause an increase in your heart rate. This means that green tea extract is suitable for use by people with high blood pressure, or other circulatory conditions, who wouldn’t normally be able to use thermogenic substances.
Green tea extract is also known to have strong chemopreventative effects (reduction in risk of cancer) possibly due to its strong anti-oxidant properties (Katiyar et al., 1993). Green tea extract, especially EGCG, is believed to exert its anticancer effects by inhibiting signalling complexes responsible for tumour cell migration and cell invasion (Rodriguez et al., 2005; Silvova et al., 2005). Green tea extract, or normal green tea consumption, appears to help to reduce the risk of breast cancer, and may help to prevent the recurrence of cancer (Seely et al., 2005). The green tea extract (specifically the polyphenol EGCG) has been shown to exert some protection against the cell-DNA damaging effects of Ultra Violet light and therefore may help to reduce the risk of skin cancer (Morley et al., 2005).
Is Green Tea extract effective? Green tea extract has proved to be highly effective at increasing the fat burning process and appears to have potent anti-cancer properties. Most researchers consider green tea to be the most effective natural weight loss product. Unlike many other weight loss products green tea extract appears to have no serious side effects.
How should I take Green Tea Extract? For, increased fat burning, weight loss, general health benefits, and an improved blood cholesterol profile you should aim to take 1 300mg capsule 1-3 times daily. Always check the potency of the capsules, only buy capsules with at least 90% polyphenol content - one popular brand sells green tea capsules with only 15% polyphenols!
Borchardt, R. T. and Huber, T. A. (1975) Catechol-O-methyl-transferase: structure-activity relationships for inhibition by flavonoids. Journal of Medicinal Chemistry. 18, 120-122.
Chantree, P. and Lairon, D. (2002). Recent Findings of green tea extract R25 (Exolise) and its activity for the treatment of obesity. Phytomedicine. 9, 3-8.
Dulloo, A. G., Seydoux, J. and Girardier, L. (1996) Tealine and thermogenesis: interactions between polyphenols, caffeine and sympathetic activity. Int J Obes Relat Metab Disord. 20 (suppl): 71 (abstr).
Dulloo, A. G., Duret, C., Rohrer, D., Giardier, L., Mensi, N., Fathi, M., Chantre, P. and Vandermander, J. (2000) Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. American Journal of Clinical Nutrition. 75, 1232-1234.
Katiyarr, S. K., Agarwal, R., Zaim, M. T. and Muhktar, H. (1993) Protection against N-nitrosodiethylamine and benzo[a]pyrene-induced forestomach and lung tumorigenesis in A/J mice by green tea. Carcinogenesis. 14 (5), 849-855.
Morley, N., Clifford, T., Salter, L., Campbell, S., Gould, D. and Curnow, A. (2005) The green tea polyphenol (-)-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage. Photodermatol Photoimmunol Photomed. 21 (1) 15-22.
Rodriguez, S. K., Guo, W., Liu, L., Band, M. A., Paulson, E. K. and Meydani, M. (2005) Green tea catechin, epigallocatechin-3-gallate, inhibits vascular endothelial growth factor angiogenic signalling by disrupting the formation of a receptor complex. Int J Cancer. 10.
Seely, D., Mills, E. J., Wu, P., Verma, S. and Guyatt, G. H. (2005) The effects of green tea consumption on incidence of breast cancer and recurrence of breast cancer: a systematic review and meta-analysis. Integr Cancer Ther. 4 (2), 144-145.
Silvova, V., Zagloga, G., DeMichele, S. J., Mukerji, P., Huang, Y. S., Siddiqui, R., Harvey, K., Valachovicova, T. and Silva, D. (2005) Green tea polyphenols modulate secretion of urokinase plasminogen activator (uPA) and inhibit invasive behaviour of breast cancer cells. Nutr Cancer. 52 (1), 66-73.
Stagg, G. V. and Millin, D. J. (1975) The nutritional and therapeutic value of tea – a review. J Sci Food Agric. 26, 1439-1459.
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