Next to water, tea is the most widely consumed beverage in the world. Black, green, and oolong tea are all derived from the Camellia sinensis plant, which contains a class of polyphenols known as catechins. Catechins, particularly those found in green tea, have been shown to exert positive effects on energy expenditure (i.e., thermogenesis) and fat oxidation, and, therefore, consumption of green tea or green tea extracts may be beneficial for weight loss. The process by which green tea is produced (heat treatment shortly after harvest) results in less oxidation and, as a result, preserves the highest concentration of catechins, which include epigallocatechin gallate (EGCG), epigallocatechin, and epicatechin gallate. Green tea also contains caffeine; therefore, the two active ingredients in green tea believed to potentially induce weight loss are caffeine and catechins, particularly EGCG.

consuming two servings of green tea containing 500–900 mg of catechins and moderate amounts of caffeine (<200 mg) for 3 months results in positive effects on body composition and reduces intra-abdominal fat in moderately overweight Chinese subjects.

Two recent meta-analyses also suggest that the catechins and caffeine in green tea result in small, but positive effects on body composition and BMI.

Hursel et al. conducted a systematic review and meta-analysis of long- term studies (≥12 weeks) that examined the effect of EGCG on weight loss and weight maintenance and included potential moderators such as regular caffeine intake and ethnicity to determine if those factors influence the effect of EGCG + caffeine on body weight. Eleven of forty-nine studies identified met the inclusion criteria for the meta-analysis. The results showed a moderate, but significant positive effect of catechins on both weight loss and weight maintenance. It was estimated that individuals in the treatment groups lost 1.31 kg more weight (~0.6 lb) compared to the CTRL groups. When the effects of habitual caffeine use and ethnicity were taken into account, the results showed that individuals who consumed caffeine in quantities >300 mg experienced less of an effect on weight loss (−0.27 kg) compared to low caffeine users (−1.61 kg).

Based upon the findings, the authors suggested that a catechin/caffeine mixture had positive effects on weight loss and that ethnicity and habitual caffeine use may moderate their effects. In a related study, Phlung et al. performed a systematic review and meta-analysis to determine the effect of catechins with or without caffeine on anthropometric variables including BMI, body weight, waist circumference, and waist-to hip ratio. Of 341 citations retrieved through their search strategy, 15 trials met the inclusion criteria and were included in the meta-analysis. The results showed that catechins + caffeine decreased BMI, body weight, and waist circumference, but had no effect on waist-to-hip ratio compared to caffeine alone. In addition, catechin + caffeine ingestion resulted in a significant decrease in body weight compared with a caffeine-free CTRL.

However, there was no effect of catechins alone on any parameter when compared to caffeine-free CTRL, suggesting that catechin ingestion alone is ineffective for weight loss. Although these studies indicate that catechins work synergistically with caffeine to elicit significant reductions in body weight, BMI, and waist circumference, the magnitude of the changes is modest at best and is not clinically relevant.

There do not appear to be any adverse side effects associated with green tea consumption, and, although it has modest effects on weight loss, there is evidence that green tea has antioxidant components that benefit health and has been shown to improve cholesterol profiles, decrease platelet aggregation, and lower blood pressure.

Caffeine

Caffeine is an active ingredient in coffee, which is another one of the most common beverages consumed worldwide, but caffeine is also found in many other foods and beverages including dark chocolate, soda, and sports and energy drinks. Caffeine has been widely studied for its potential thermogenic effects and has been shown to increase REE and reduce energy intake; however, these acute effects have not resulted in meaningful long-term weight loss. Caffeine is usually studied in combination with other thermogenic ingredients for their effects on weight loss versus its effects alone; however, one 12-year longitudinal study showed that men and women who increased their caffeine consumption (143–213 mg) experienced slightly smaller weight gain (2.79–3.22 kg) compared to individuals who decreased their caffeine intake (3.87–4.28 kg) over the 12-year period. A lack of sensitivity to caffeine as a result of increased tolerance may explain, in part, why it is ineffective for weight loss over time.