GREEN TEA & METABOLISM

Green Tea & Metabolism

Green Tea & Metabolism

1• Introduction

In a study reported on in the American Journal of Clinical Nutrition, it was found that green tea extract resulted in a significant increase in energy expenditure (a measure of metabolism), plus also had a significant effect on fat oxidation• While some of the effects were originally theorized to be due to the caffeine content of green tea, the researchers discovered that the tea actually has properties that go beyond those that would be explained by the caffeine• The same amount of caffeine as was in the green tea, administered alone, failed to change energy expenditure in other studies• This led reseachers to believe that there is some interaction going on with the active ingredients of green tea that promotes increased metabolism and fat oxidation•

Tea catechins vary across tea tree and preparations, especially for EGCG and ECG contents• Tea with large leaves usually has less EGCG compared with tea with small leaves• Tea should be consumed around 50°C• For better quality control, current chemoprevention or intervention trials usually use dry tea extracts in capsules that can be chemically measured for the exact concentration of each tea component• A traditional dose for human studies is 400 to 1500 mg tea per day according to published studies• The composition of green tea is quite stable in its dry condition• The shelf life for EGCG, EC, ECG, and epigallocatechin as well as the mixture is longer than 1 year in a dry condition and can be oxidized in 30 minutes in water•

The bioavailability of EGCG or catechins, however, is relatively low due to its short half-life by nature• The short half-life in vivo of EGCG, which ranges from 1•87 to 4•58 hours from a 50- to 1600-mg dose ( 0•7-23 mg/kg body weight, based on 70 kg body weight), might be overcome by repeated administration because of its reported low toxicity and high tolerance by human subjects, even when given in doses as high as 1600 mg ( 23 mg/kg body weight)•

Tea is one of the safest beverages since it is made with boiling, sterile water• It is also one of the most widely consumed beverages, second only to water, and has been popular for over 4000 years (Weisburger, 1997)• Tea, from the plant Camellia sinensis, is consumed in different parts of the world as green (20%), black (78%) or oolong tea (2%)• Green tea is favored mostly in Japan and China (Kuroda and Hara, 1999)• Initial research on the benefits of green tea was carried out in Japan and China because of their local drinking customs• Green tea is now an acknowledged cancer preventive beverage in Japan ( Fujiki et al•, 1999)• The Second International Symposium ( Anon•, 1999) reported on investigations on green and black tea•

Drinking green tea and/or ingesting green tea bioactive compounds may mitigate bone loss in elderly women and men, thereby decreasing their risk of osteoporotic fractures• ...