Chances are you have heard green tea referred to as a superfood. It’s no wonder, as green tea has been connected with the treatment of heart disease, cancer, diabetes, inflammatory bowel disease and liver disease.¹ The health benefits seem endless and we can’t seem to get enough. Every trendy cafe now boasts multiple green tea options, including iced tea, lattes and matcha powders.
Green tea has recently become a popular option for weight loss due to celebrity attention, such as endorsement segments on Doctor Oz’s show. Natural products are currently very popular, making green tea an appealing option for those who are looking to lose weight. But is green tea really the superfood we’ve made it out to be?
An eight ounce serving of green tea contains about 50 mg of caffeine. Caffeine effects the body by increasing epinephrine, also known as adrenaline. This can cause increased alertness, decreased fatigue, as well as increase the amount of calories burned.²
An eight ounce cup of green tea also contains approximately 50-100 mg of catechins. These are a type of flavonoid antioxidant. Catechins are thought to increase the amount of norepinephrine in the body, which is similar to adrenaline. Increased norepinephrine can increase the breakdown of fat and amount of calories burned.³
The combination of catechins and caffeine in green tea is what has led researchers to believe that green tea could cause weight loss. Scientists created concentrated green tea extracts in supplement form to study the effects of high doses of caffeine and catechins. These supplements have been used in the majority of research on green tea as a weight loss tool.
Overall, study results are mixed. Most studies show that people who take green tea supplements have more weight loss than those who do not take supplements. However, it only adds up to a few extra pounds at most.⁴⁻⁶
The extra weight loss may also not be due to just the green tea supplements alone. Differences in lifestyle were not considered in many of the studies. These differences can include calorie intake, physical activity, or extra caffeine intake. Any lifestyle differences between people in the studies could easily skew weight loss results.
There are also risks with taking green tea supplements. Catechins are considered safe with a max intake of 800mg/day for up to 4 weeks.⁷ However, studies have shown that frequently taking high doses of catechins can be harmful to the liver.⁸˒⁹
High doses of green tea may also affect how your body absorbs nutrients and medications.⁷ Vitamin K is in green tea, which can interfere with blood thinner medications like Coumadin. Green tea can also reduce your body’s ability to absorb iron and folic acid. The more green tea products you consume, the greater the risk.
These risks are just from studying supplements on a short-term basis. The risks of taking high dose green tea supplements for long periods of time has not been determined. More research needs to be done so that we better understand the effects of green tea on weight loss and the potential risks of taking the products.
Another concern is that supplements do not need to be regulated by the government. Supplements do not always contain the amount of catechins which is claimed on the label.¹⁰ Catechins have also been found in supplements where they’re not supposed to be. This makes it difficult to determine the amount of catechins you’re actually getting.
So what about just drinking green tea? You would need to drink approximately 10 cups of tea in order to reach the high doses of catechins in the supplements used for weight loss. This means drinking a cup or two of green tea a day will most likely not help you lose weight. Fitting in 10 cups per day is impractical – not to mention sounds miserable!
You should also be careful of any weight loss method that offers a quick, easy solution. The effects of green tea alone are not enough to cause significant results. Taking supplements without changing lifestyle habits has a very small chance of being a successful weight loss plan. There may be a place for green tea extract in your diet, but a weight loss plan should not be built around taking supplements.
- Ehrlich S. Green tea. University of Maryland Medical Center Complementary and Alternative Medicine. http://umm.edu/health/medical/altmed/herb/green-tea. 2015. Accessed January 21, 2017.
- Icken D, Feller S, Engeli S, Mayr A, Muller A, Hilbert A, de Zwaan M. Caffeine intake is related to successful weight loss maintenance. Eur J Clin Nutr. 2016;70:532-534.
- Rains TM, Agarwal S, Maki KC. Antiobesity effects ofgreen tea catechins: a mechanistic review. J Nutr Biochem. 2011;22.
- Jurgens TM, Whelan AM, Killian L, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane DB Syst Rev. 2012;12:8650.
- Hursel R, Viechtbauer W, Westerterp-Plantenga MS. The effects of green tea on weight loss and weight maintenance: a meta-analysis. Int J Obes. 2009;33:956-661.
- Phung OJ, Baker WL, Matthews LJ, Lanosa M, Thorne A, Coleman CI. Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis. Am J Clin Nutr. 2009;91:73-81.
- Sarma D, Barrett M, Chavez M, et al. Safety of green tea extracts: a systematic review by the US pharmacopeia. Drug Saf. 2008;31:469-484.
- Navarro VJ, Bonkovsky HL, Hwang S, Vega M, Barnhart H, Serrano J. Catechins in dietary supplements and hepatotoxicity. Dig Dis Sci. 2013;58:2682-2690.
- Emoto Y, Yoshizawa K, Kinoshita Y, et al. Green tea extract-induced acute hepatotoxicity in rats. J Toxicol Pathol. 2014;27:163-174.
- Waterhouse AL. Consumer labels can convey polyphenolic content: implications for public health. Clin Dev Immunol. 2005;1:43-46.