Evidence Level
Green Tea Extract (EGCG), a natural compound derived from green tea, has been studied for its potential thermogenic and metabolic effects. A systematic review by Jurgens et al. (2012) of randomized controlled trials (RCTs) involving 532 participants outside Japan and 1030 in Japan found that green tea may modestly aid weight loss, though evidence remains inconsistent across studies. The primary mechanism involves COMT inhibition, which prolongs norepinephrine signaling and enhances energy expenditure (Dulloo et al., 1999). In a trial with 10 men, green tea extract increased 24-hour energy expenditure by 4% and decreased respiratory quotient compared to placebo.
Safety considerations are important, as high doses of EGCG have been linked to hepatotoxicity (Ortsäter et al., 2012). It is recommended to consume no more than 800 mg per day with food. While EGCG improves glucose tolerance and preserves islet structure in animal models of type 2 diabetes (Ortsäter et al., 2012), its efficacy in human psychiatric conditions remains unproven, as shown by a study where EGCG supplementation did not significantly improve symptoms in individuals with schizophrenia or bipolar disorder (Loftis et al., 2013).