AKA: Oolong Tea, Tea, Camelia Sinensis
The Mythology: Speeds up metabolism and burns fat
The Truth: Speeds up metabolism and burns fat!
Research: Green Tea is rich in tannin like substances called Catechins. In Black Tea, Catechins are oxidized during the fermenting process leading to their conversion into Theaflavins and Thearubins. Apparently these are less potent antioxidants than ones found in green tea. Green tea, oolong tea and white tea are consumed primarily in China, Japan and a few countries in North Africa and the Middle East. Tea is made from the leaves of Camellia Sinensis L. species of the Theaceae family, Green Tea being the non-oxidized, non-fermented product, Oolong Tea the semioxidized, semifermented product; White Tea is made from the youngest buds of the plant that undergo even less processing than green tea.
As a consequence of this, all teas contain high quantities of several polyphenolic components such as epicatechin, epicatechin gallate, epigallocatechin and, the most abundant and probably the most pharmacologically active, epigallocatechin gallate. Tea leaves that have been processed the least contain the most catechins. From caffeine, that is also present in green tea, it has been reported that it has thermogenic effects and can stimulate fat oxidation in vitro, in part through sympathetic activation of the central nervous system.
Green tea has been very well studied. Numerous trials in recent years have concluded that energy expenditure and fat oxidation are increased. A number have also demonstrated increases in weight loss and favorable changes in body composition. These studies have proven their efficacy both in Asian and Caucasian populations. 2.3. While some studies have not demonstrated an effect, these appear to be in a minority.
Also Westerterp Plantenga (2005) found that weight loss with Green Tea was only significant in low habitual coffee consumers. My feeling is that people who want to get the most out of Green Tea thermogenesis need to cycle their Green Tea consumption and have regular caffeine breaks for at least a few days to prevent their bodies from adapting to it.
Does Green Tea work better when combined with other well known thermogenics like caffeine and capsaicin? No one knows for sure but the evidence points to a definite maybe.
References
1) Int J Obes (Lond), 2010 Apr;34(4):659-69, Epub 2010 Feb 9, Thermogenic ingredients and body weight regulation.
Hursel R, Westerterp-Plantenga MS.
2) Chantre P, Lairon D, Phytomedicine 2002; 9: 3–8, Recent findings of green tea extract AR25 (Exolise) and its activity for the treatment of obesity.
3) Wang H, Wen Y, Du Y, Yan X, Guo H, Rycroft JA et al. Obesity 2009 e-pub. Effects of catechin enriched green tea on body composition.
Adverse effects: A possible side effect of green tea consumption is a minor increase in blood pressure. However the change is not considered to be significant.
How it works: Catechins in green tea upregulate lipid-metabolizing enzymes and thereby stimulate fat oxidation. Catechins also inhibit COMT that leads to a increase in norepinephrine and adenyl cyclase. Glucose uptake is decreased and lipolysis is enhanced. Caffeine antagonizes adenosine that usually decreases levels of norepinephrine. Stimulation of sympathetic nervous system, hormone sensitive lipase and upregulation of UCPs lead to an increased energy expenditure and fat oxidation.
