This clinical study was undertaken to evaluate the effects of green tea extract and metformin, both individually and in combination, on type 2 diabetes risk factors and obesity in nondiabetic overweight women. The study was conducted at the Clinical Hospital of Federal University of Goias, Brazil. The green tea used in the study contained 500 mg of Camellia sinensis leaf extract with 280 mg polyphenols, including catechins. The working hypothesis of the study was that green tea would reduce glycaemia through changes in body composition. Using defined eligible criteria, 120 subjects were recruited into the study. A 12-week randomized, double-blind, placebo-controlled design was used. The participants were randomized into four groups: Placebo (PC), 4 capsules containing microcrystalline cellulose/day (1 g/day); Green tea (GT), 2 capsules containing dry extract of green tea/day (1 g/day, 560 mg polyphenols) + 2 capsules containing placebo/day; Metformin (MF), 2 capsules containing metformin (1 g/day) + 2 capsules containing placebo/day; Green Tea + Metformin (GTMF), 2 capsules containing dry extract of green tea/day(1 g/day; 560 mg polyphenols) + 2 capsules containing metformin/day (1 g/day). All of the capsules had the same appearance. Data was analysed using regular statistical methods for significant differences. Their results showed:
- No significant interactions in glycemic control
- Green tea in the absence of metformin reduced fasting glucose significantly
- When combined with metformin the lowering effect was not observed.
- Metformin increased HbA1c concentration and also reduced body weight and lean mass significantly
- Green tea significantly reduced total cholesterol and LDL-C.
Based on these observations, the authors conclude that green tea extract was superior to metformin in improving glycemic 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.
COMMENTARY: Results from this clinical study are encouraging in view of the importance of the prevalence of obesity and Type 2 Diabetes in the general population and their prevention, treatment and management. The study was designed well with proper controls and use of the recognised markers of obesity and diabetes. Some of the concerns with this study include: 1. High numbers of subject drop outs following recruitment. No reasons were given for this by the authors. 2. The observed results with mono treatment with metformin was surprising. Authors suggest that the effect of metformin may be associated with the expression of specific genes. They also point out that the polyphenol found in green tea extract – epigallocatechin gallate (EGCG) may be more effective in Asians since they carry a specific polymorphism that can influence adrenergic-induced lipolysis. Both these observations indicate the involvement of genetic facts that influence the effects of green tea polyphenols as well as metformin. Therefore, care should be taken in applying the observed results of this study to a general population representing genetic heterogeneity. Overall it is a well executed study having important applications for the management of obesity and diabetes.
Alves Ferreira, M., et al. Clinical Nutrition ESPEN 22 (2017) 1-6