Green Tea Extract Increases Insulin Sensitivity & Fat Burning during Exercise

Chasing your burger and fries with a mug of green tea may be a good idea. (Photo by w00kie)

The effect of green tea on weight loss and insulin sensitivity is still relatively unknown. There are some promising studies out there, but conflicting data also exists, making it difficult to put all the pieces together. For now, however, the good news for green tea keep coming.

Since most of the studies are either done in vitro, in animals or in human subjects suffering from various conditions such as diabetes, coming across a study on healthy subjects is always interesting. In their paper, Venables et al. investigated the effect of green tea extract on glucose tolerance and fat oxidation during moderate-intensity exercise in healthy young men.

Green tea extract and fat burning during exercise

In the first experiment, each participant completed a 30-minute cycling exercise before and after green tea supplementation in a crossover design. The average relative exercise intensity was similar in both trials. However, fat oxidation (which is the technical term for "burning" fat) was significantly higher when the participants had taken the green tea extract supplement (0.41 vs. 0.35 g/min). The ratio of fat to carbohydrates used for energy expenditure was also higher in the green tea group than in the placebo group.

Green tea extract, glucose tolerance and insulin sensitivity

In the second experiment, the participants took an oral glucose tolerance test. Before consuming 75 of glucose, half of the subjects took green tea capsules containing 890 mg of polyphenols of which 366 mg was epigallocatechin gallate, EGCG. The other half took a corn-flour placebo.

Plasma glucose concentrations after the oral glucose tolerance test were similar in the placebo and green tea extract groups. Serum insulin was significantly lower in the green tea group, however; the area under curve (AUC) was 15% smaller in those who had taken a green tea supplement before the test.

Conclusion

A green tea extract containing 890 mg polyphenols (catechins) increased fat oxidation from moderate-intensity exercise compared to placebo in healthy young men. Green tea extract also reduced insulin area under curve during a 2-hour oral glucose tolerance test and improved insulin sensitivity. Green tea may thus help with weight loss, both by increasing fat metabolism during exercise and maintaining healthy insulin levels.

For more information on green tea, see these posts:

Green Tea Extract Enhances Abdominal Fat Loss from Exercise
Peak Increase in Antioxidant Activity Occurs 20-40 Minutes after Drinking Green Tea
Green Tea, Black Tea & Oolong Tea Increase Insulin Activity by More than 1500%
Green Tea Reduces the Formation of AGEs