All whole plant foods contain fiber, many different fruits and vegetables are rich in vitamin C, and many orange vegetables and fruits are rich in beta-carotene. Some nutrients and phytochemicals are more specific. Lycopene is far more concentrated in cooked tomatoes than any other food, isothiocyanates are formed only by members of the cruciferous vegetable family, punicalagin is found only in pomegranate, and epigallocatechin-3-gallate (EGCG) is found almost exclusively in tea, especially green tea.1
What’s the difference between green, black, and white teas?
All types of tea are made from the Camellia sinensis plant, and the different types are based mostly on processing methods. During the “fermentation” process, the tea leaves are broken or rolled, and oxidation changes the phytochemical makeup of the tea. White tea is made from buds and young leaves, and green tea from more mature leaves; both white and green teas are unfermented. During fermentation, the flavonoids characteristic of green tea (catechins such as EGCG) are converted to those that are characteristic of black tea (theaflavins and thearubigins). The longer the tea leaves are fermented, the less EGCG there will be. Oolong tea is semifermented, and black tea is fully fermented.2
|EGCG (mg/100 g brewed tea)1|
|Decaffeinated green tea||26.05|
Drinking green tea regularly has been linked to reduced risk of heart disease, stroke, lung cancer, breast cancer, prostate cancer, diabetes, and all-cause mortality.3-11 Green tea is also thought to help prevent or slow brain aging.12,13
Green tea catechins are thought to affect energy metabolism, and green tea supplementation has been investigated for potential effects on weight loss, but no significant reductions in weight have been reported.14
An analysis of 5 studies found a dose-dependent 10 percent decrease in coronary artery disease risk for each cup of green tea consumed daily; there was no such effect for black tea.3 Randomized controlled trials have shed light on how this might work, showing that drinking green tea or using green tea extract supplements:
Many anti-cancer effects have been attributed to green tea catechins:
Brewed tea or supplements?
Green tea polyphenols can add to the spectrum of phytochemicals provided by green vegetables and other plant foods; a daily cup or two of green tea is a healthful adjunct to a high-nutrient diet. Green tea extract supplements are also an option, but they are very concentrated, commonly providing EGCG levels equivalent to five, ten, or even twenty cups of tea. The more concentrated supplements may be appropriate in some cases, but more than necessary for most people. Green tea extract supplements are sometimes but not always decaffeinated.
Regular or decaf?
Caffeine content varies with the type of green tea, brewing method, and steeping time, but in general green tea contains less caffeine than black tea, and black tea contains less than coffee. A study of commercially available tea bags found that black teas had a caffeine content ranging from 27 to 61 mg per 6 ounce cup, and green tea 36 to 41 mg, when steeped for 5 minutes.36 Catechins are released somewhat slowly, so a longer steep time is better; green tea steeped for five minutes has more than four times the catechins compared to one minute.37 If you prefer iced tea, antioxidant activity was found to be similar in green teas steeped in hot water for seven minutes compared to cold water for two hours.38
Note in the table above that the EGCG content is lower in decaffeinated green teas, but still substantially more than black tea. To add some green tea catechins to your diet while minimizing the caffeine content, you can opt for a decaffeinated green tea. Some teas use the solvent methylene chloride, which has been found to be carcinogenic in animals.39 Ethyl acetate is another common solvent used in teas; these teas are often labeled “naturally decaffeinated,” because ethyl acetate is a naturally occurring plant compound; it is only thought to pose a risk in very high doses (via inhalation) in occupational settings.40 Teas using the carbon dioxide decaffeination process are probably the best choice. Tea company websites often specify their decaffeination method.
Drink green tea plain
It is best to drink green tea plain, since there is evidence that adding milk (dairy or not) may blunt some of the benefit, possibly because of an interaction between proteins and tea polyphenols. The study suggested that adding milk blocked the improvements in endothelial function commonly observed with tea intake.41 It is thought that soy milk has a similar effect.42
Loose tea or tea bags?
Brewing loose tea or using powdered green tea (matcha) produces less waste than tea bags, and some of the newer “sachet” tea bags contain plastic compounds that may have endocrine disrupting effects. Also, some paper tea bags are coated with epichlorohydrin, a potential carcinogen.43-46 If you use paper tea bags, it is best to look for teas that use unbleached paper tea bags that do not contain epichlorohydrin.
Remember, it is not one particular food or nutrient that will best assure your long-term health and protection against cancer, but the regular consumption of a wide variety of beneficial plant compounds. Green tea clearly has beneficial properties, but these benefits may be more pronounced in those who have a poor diet compared to those already consuming an array of phytochemicals in a Nutritarian diet.
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Jurgens TM, Whelan AM, Killian L, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev 2012, 12:CD008650.
Liu K, Zhou R, Wang B, et al. Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials. Am J Clin Nutr 2013, 98:340-348.
Zheng XX, Xu YL, Li SH, et al. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am J Clin Nutr 2011.
Khalesi S, Sun J, Buys N, et al. Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials. Eur J Nutr 2014, 53:1299-1311.
Alexopoulos N, Vlachopoulos C, Aznaouridis K, et al. The acute effect of green tea consumption on endothelial function in healthy individuals. Eur J Cardiovasc Prev Rehabil 2008, 15:300-305.
Tinahones FJ, Rubio MA, Garrido-Sanchez L, et al. Green tea reduces LDL oxidability and improves vascular function. J Am Coll Nutr 2008, 27:209-213.
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Peng G, Dixon DA, Muga SJ, et al. Green tea polyphenol (-)-epigallocatechin-3-gallate inhibits cyclooxygenase-2 expression in colon carcinogenesis. Mol Carcinog 2006, 45:309-319.
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