Green tea extract outperforms metformin in lipid profile and glycaemic control in overweight women: A double-blind, placebo-controlled, randomized trial

Summary Background & aims Both green tea and metformin are used as adjuvants to treat and prevent complications associated with obesity; however, studies comparing their action and interaction in non-diabetic overweight women have not been reported. Thus, the current study evaluated the effects of green tea extract and metformin, both individually and in combination, on type 2 diabetes risk factors in non-diabetic overweight women. Methods A total of 120 overweight women were randomly assigned in a double-blind manner to 1 of 4 groups, as follows: control ( n  = 29; 1 g of cellulose), green tea ( n  = 32; 1 g of dry green tea extract), metformin ( n  = 28; 1 g of metformin), and green tea + metformin ( n  = 31; 1 g of dry green tea extract + 1 g of metformin). Each group took the indicated capsules daily for 12 weeks. Anthropometric measurements, body composition, and fasting blood samples were evaluated. Results Although no significant interactions were observed in glycaemic control ( p  = 0.07), green tea in the absence of metformin reduced fasting glucose (−4.428 ± 2.00; p  = 0.031), but when combined the lowering effect was nullified. In contrast, metformin increased HbA1c concentration (0.048 ± 0.189%; p  = 0.017) and also reduced body weight (−1.318 ± 0.366 kg; p  = 0.034) and LM (lean mass) (−1.249 ± 0.310; p  = 0.009). Regarding lipid parameters, green tea significantly reduced total cholesterol and LDL-c. Conclusions Green tea was superior to metformin in improving glycaemic control and lipid profile in non-diabetic overweight women and, therefore, green tea extract is a promising alternative for reducing type 2 diabetes risk in overweight women.