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Some dieters say that green tea promotes weight loss.
Green tea is a good choice for people on a weight-loss program because it can help them to lead a healthier lifestyle. For example, substituting green tea for coffee with cream and sugar not only saves calories but also supplies a lot of healthful substances, such as polyphenols and flavonoids, that can help improve one's overall health.
Green tea contains a small amount of caffeine, so it serves as a mild appetite suppressant as well.
Test tube studies suggest that green tea extracts high in catechins may inhibit fat digestion and a preliminary human study found a green tea extract increased calorie burning.1, 2 A preliminary human study found that people taking a green tea extract containing 375 mg per day of total catechins (of which 270 mg per day was epigallocatechin gallate) for three months lost an average of 4.6% of their body weight without dieting.3 Double-blind trials are needed to confirm this effect.
Green tea is generally free of side effects. The most common adverse effects reported from consuming large amounts (several cups per day) of green tea are insomnia, anxiety, and other symptoms caused by the caffeine content in the herb.
An extract of green tea taken by healthy women with a meal inhibited the absorption of non-heme iron (e.g., the form of iron in plant foods) by 26%.4 Frequent use of green tea could, in theory, promote the development of iron deficiency in susceptible individuals.
There have been at least 34 case reports of people developing liver damage (sometimes severe) while consuming weight-loss products that contained concentrated extracts of green tea.5 A cause–effect relationship was not proven, and most of the products contained other ingredients in addition to green tea extract. However, researchers have concluded that green tea extract was the probable cause of liver damage in some of the cases.6 Scientists have cautioned against the use of large amounts, or concentrated extracts, of green tea. In addition, there is a case report in which a person developed thrombotic thrombocytopenic purpura (a condition in which a bruising develops as a result of a low platelet count) after consuming a weight-loss product that contained green tea extract for 2 months. Green tea was not proven to be the cause of this problem.7
Certain medicines interact with this supplement.
Tannins are a group of unrelated chemicals that give plants an astringent taste. Herbs containing high amounts of tannins may interfere with the absorption of ephedrine or pseudoephedrine taken by mouth. Herbs containing high levels of tannins include green tea, black tea, uva ursi (Arctostaphylos uva-ursi), black walnut (Juglans nigra),red raspberry (Rubus idaeus), oak (Quercus spp.), and witch hazel (Hamamelis virginiana).
One man taking warfarin and one-half to one gallon of green tea (Camellia sinensis) per day developed signs based on laboratory testing suggesting his blood was too thick because the green tea was blocking the effect of warfarin. Removal of the green tea caused normalization of his blood tests. Those taking green tea and warfarin together should have their blood monitored regularly to avert any problems and should consult with a doctor, healthcare practitioner and/or pharmacist before taking any medication.
Last Review: 05-23-2015
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