Green tea contains polyphenols that work as antioxidants in your body. They help protect cells from free radical damage. Decaffeinating the green tea does have some effect on the healthy components, but doesn't eliminate them.
It looks like the decaffeinating process may reduce the amount of flavanol, which is a polyphenol. According to one study on green tea, the flavanol content varied from 21.2 to 103.2 mg/g (milligram per gram) for regular teas, while the flavanol content of the decaf green tea ranged from 4.6 to 39.0 mg/g. The antioxidant values varied from 728 to 1,686 trolox equivalents/g tea for regular teas and from 507 to 845 trolox equivalents/gram for decaffeinated teas.
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