Green Tea - Metabolism Enhancer

A growing body of research is confirming one of the benefits of green tea. Metabolism of fats are believed to be increased by catechins and caffeine contained in green tea, leading to decreased body mass index (BMI), body weight and waist circumference. However, green tea metabolism may cause significant liver damage, thus caution must also be exercised.

Green Tea’s Mechanism of Action

Green tea has long been believed to fight fat. Substances in green tea called catechins especially epigallocatechin gallate (EGCG) increases thermogenesis, a process that generates body heat which is directly linked to the utilization of fats. Thermogenesis is controlled by the body’s sympathetic nervous system, triggered by a substance called norephinephrine.

Inhibitors of norephinephrine include substances called monoamine oxidase (MAO) or catechol-O-methyl transferase (COMT). It is proposed that EGCG blocks the activity of COMT, thus favoring more thermogenesis and less fat. Out of all the varieties of tea, catechins are believed to be more abundant in the less processed and unfermented green tea. Metabolism is therefore increased with the intake of green tea.

Supporting Evidence

The metabolic-enhancing effect of green tea may be a result of the synergism of catechins and caffeine, both of which are found in green tea. In a systematic review of clinical trials done on green tea, Phung et al stated that participants given green tea catechins and caffeine reported a decrease in BMI, body weight and waist circumference. However, green tea catechins alone do not alter these measurements significantly.

For those who do not like the bitter taste of green tea, a coated tablet of green tea extract might work just as well. In 2009, Di Pierro et al demonstrated significant weight loss and decreased BMI in a group of participants who were placed on a low-calorie diet and given green tea extracts compared to the group who were on the hypocaloric diet only. Both groups also exhibited improved cholesterol profiles with no statistically significant difference between the two groups.

A Word of Caution

While this has been welcomed by dieters, the medical community has cautioned against the indiscriminate use of green tea supplements as green tea metabolism may result in marked liver toxicity. Patients may present with abdominal pain and jaundice (yellowing of the eyes and skin). The mechanism of injury is yet unknown. Studies have been unable to prove that EGCG is the responsible agent so other causes have been hypothesized such as an allergic reaction to the green leaf or a component of the extract. The leaves could also have been contaminated during cultivation, harvest or processing. Such cases have been sporadic but the US Pharmacopeia Dietary Supplements Information Expert Committee has recommended that all green tea supplements carry labels suggesting that the supplement must be taken with food. It should also warn consumers of the potential adverse effects.

Green tea is just one of many supplements spawned by pharmaceutical companies to cater to a growing population interested in keeping healthy. It has been used in the hopes of inducing weight loss with the support of new studies that show its link to moderate weight loss. However, possible liver toxicity from green tea metabolism should give one pause in making this a quick, no-sweat route to losing weight.