Several studies have shown that drinking green tea appears to help you lose bodyfat, perhaps because of its caffeine and its potent antioxidants, which may increase resting metabolism. Some studies show that green tea inhibits the enzyme lipase, which is required to digest fat. Other studies show that both black and green teas inhibit the activity of alpha-amylase, an enzyme involved in carbohydrate, especially starch, digestion.
While many studies examining the effects of tea on enzyme activity have had an in vitro or test-tube, design, a newer study looked at the effects of black, green and mulberry teas on human subjects.1 In it subjects took concentrated tea extracts before eating meals containing either carbohydrates or fat.
The tea extracts didn’t affect fat absorption but did induce a 25 percent malabsorption of carbohydrates. The active ingredients in the extracts were the equivalent of drinking five to 20 cups of tea daily. The authors note that if you ate 400 grams of carbs daily, reducing the absorption of 25 percent of those carbs would lead to a loss of 16 kilograms, or 35 pounds, of fat a year with no other changes in diet or exercise. They also warn, however, that inhibiting that much carb absorption could lead to some side effects, such as intestinal gas and diarrhea.
Another study examined the effects of the active ingredients in tea, the polyphenols, on digestive enzymes that break down carbs (a-amylase), fat (lipase) and protein (pepsin, trypsin).2 The in vitro experiment found that in the presence of 0.05 milligrams per milliliter of tea polyphenols, a-amylase, pepsin, trypsin and lipase activity was inhibited by 61 percent, 32 percent, 38 percent and 54 percent, respectively
The interference with protein-digesting enzymes (pepsin and trypsin) may be a problem for bodybuilders. It isn’t clear from the study how much of the tea polyphenols would produce the effect. Odds are, though, that a high concentration would be required. That’s consistent with previous studies showing high levels of green tea interfered with thyroid function. The amount needed to produce the effect would be hard to reach, and the same may be true for protein enzymes. Those who are concerned may opt to take green tea supplements separately from when they have protein meals and supplements. You wouldn't want to go overboard with green tea supplements anyway, since high doses are linked to liver problems.
The enzyme inhibition promoted by tea polyphenols was considerably more potent for fat and carbs than protein. For those seeking to lose bodyfat, taking tea supplements with meals high in fat or carbs may prove beneficial. Recent research shows that ingesting green tea supplements with milk proteins, such as whey or casein, causes the active polyphenols in the tea to bind to the proteins, possibly inactivating the polyphenols. For this reason, it's best to ingest any type of tea supplement away from concentrated milk protein supplements.
References
1 Zhong, L., et al. (2006). An extract of black, green and mulberry teas causes malabsorption of carbohydrate but not of triacylglycerol in healthy volunteers. Am J Clin Nutr. 84:551-555.
2 He, Q., et al. (2006). Effects of tea polyphenols on the activation of a-amylase, pepsin, trypsin, and lipase. Food Chemistry. 101:1178-82.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited. 
