A new study shows that teas of various types—with the exception of herbal teas—potently increase insulin activity.1 The study used an in vitro model, or isolated cells, specifically fat cells, known to respond to products that improve insulin activity. Exposing the isolated cells to various types of tea, including green, black and oolong teas, led to a 15-fold increase in insulin activity.
The active ingredients in such teas are compounds collectively known as polyphenols. Of the natural polyphenols found in tea, the most potent is epigallocatechin gallate. Although such teas also contain caffeine, the study showed that caffeine had an insignificant effect on insulin activity.
Adding lemon to the tea had no effect on the tea’s insulin activity either. But adding five grams of 2 percent milk decreased the insulin-potentiating effect by 33 percent, while adding 50 grams caused a 90 percent drop. Adding nondairy creamers or soy milk likewise lowered insulin activity induced by tea. The active polyphenol content of the teas is deactivated when it binds to milk molecules.
Prior studies have shown that tea inhibits a starch-digesting enzyme called amylase and thereby may inhibit the complete absorption of carbohydrates. Other studies show that tea has a similar effect on lipases, enzymes that digest fat, leading to a drop in fat absorption. Since this new study didn’t involve any carb consumption, the logical conclusion is that the tea polyphenols have a direct effect on insulin itself.
One question arises: If tea affects insulin release, and insulin is known to promote lipogenesis, or bodyfat synthesis, wouldn’t drinking tea with carbs lead to increased bodyfat? That isn’t the case, simply because tea enhances insulin activity. Because it makes insulin work better, the body has to secrete less insulin in response to a meal. Less insulin means less bodyfat formation. If anything, tea appears to interfere to a minor degree with both carb and fat uptake, which would be beneficial.
The unanswered question is how much tea you should drink to obtain those beneficial effects. That remains to be determined by future research, but the protective effects seem to depend on drinking a minimum of four to five cups a day. You can also get that level of active tea polyphenol from two capsules of a standardized green tea supplement.
1 Anderson, R.A., et al. (2002). Tea enhances insulin activity. J Agric Food Chemistry. 50:7182-7186.
©,2011 Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
