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Green tea has long been consumed for its health properties. Along with its ability to boost mental alertness, the beverage has been said to burn fat, and potentially to protect against heart disease and cancer.
Claims like these are what draw consumers to supplements made from green tea extract, which is now a common ingredient in weight loss or fat burning supplements. In 2020, consumers spent approximately $141 million on green tea supplements, according to the latest data from Nutrition Business Journal. And tea itself, including green tea, is the most commonly consumed beverage in the world aside from water.
So does the scientific data back up claims that green tea burns fat or boosts your overall health? We reviewed the research and spoke to experts to find out.
Will Green Tea Help With Weight Loss?
It’s true that green tea can raise your metabolic rate, so you burn more calories, says David Nieman, DrPH, director of the human performance laboratory at Appalachian State University in Boone, N.C. Nieman, who has studied green tea extensively, says this effect is probably due to a combination of its caffeine and catechins—antioxidants that are plentiful in green tea and present in smaller amounts in some fruits, dark chocolate, and red wine.
But the effect is likely to lead to little, if any, change on the scale. “People think if you drink a few cups of green tea, you’ll see the fat melt away,” Nieman says. “That’s just not going to happen.”
And the evidence that supplements derived from green tea do much for weight loss is minimal. Some studies have found modest reductions in body weight associated with green tea supplementation, according to the National Institutes of Health Office of Dietary Supplements. But other human trials have found no benefit. "Taken together, the findings of these studies suggest that if green tea is an effective weight-loss aid, any effect it has is small and not likely to be clinically relevant," write the authors of an NIH fact sheet.
What’s more, experts warn against taking the large amounts used in many studies—and recommended on many supplement labels. There have been reports of serious liver damage in people who used green tea supplements.
And one study published in 2017 in the journal Cancer Prevention Research found that postmenopausal women who’d taken green tea extract twice a day for a year as part of a breast cancer clinical trial had elevated liver enzymes—a sign of potential liver damage often seen in people who abuse alcohol.
“This level of intake may well border on the toxic range,” says Jay H. Hoofnagle, MD, director of the Liver Disease Research Branch at the National Institutes of Health. The potential risk of liver damage is one reason green tea extract is included on CR’s list of 15 supplements you should never take.
Still, when it comes to losing weight, working a few cups of brewed green tea into your diet isn’t necessarily a bad idea. If you don't add sugar, it's calorie-free and can be a good replacement for sugary drinks.
Consumption of up to eight cups a day is believed to be safe, according to NIH, though people that are pregnant or breastfeeding should not have more than six cups daily to limit caffeine intake.
Does Green Tea Prevent Cancer?
Compounds called catechins are often credited for green tea’s cancer-fighting potential. These antioxidants have the ability to block the action of molecules called free radicals, which can cause changes in healthy cells that sometimes lead to cancer. But there’s no solid proof yet that the catechins in green tea help to prevent cancer in humans, despite some promising studies in test tubes and animals.
In 2009 the Cochrane Library published a review of 51 studies that included a total of more than 1.6 million participants. Each study investigated whether consuming green tea reduced the risk of developing specific types of cancer, including those of the breast, colon, oral cavity, liver, pancreas, and prostate.
The results were conflicting, says lead author Katja Boehm, PhD, a health psychologist at Private University Witten/Herdecke in Germany. After scrutinizing the data, Boehm says, the evidence of a benefit wasn’t strong enough to recommend using green tea to protect against cancer.
In a 2020 update to that review, the authors concluded that the evidence for a beneficial effect against cancer remains limited, with inconsistent results between studies.
Can Green Tea Prevent Heart Disease?
For example, in a study of more than 40,500 adults, researchers in Japan found that those who consumed five or more cups of green tea per day were 26 percent less likely to die of cardiovascular disease over an 11-year period than those who drank just one cup per day.
Similarly, a study of 76,979 people published in the Journal of Epidemiology and Community Health in 2011 found that women who drank one to six cups of green tea per day had a reduced risk of dying of cardiovascular disease (over an average of 13 years) compared with those who drank none.
How might green tea protect the heart? Experts say it may reduce high cholesterol levels and high blood pressure, which are important factors in cardiovascular disease.
But while this is a potential benefit, it's not conclusive, and high doses of green tea can reduce the effectiveness of the drug nadolol, used to treat high blood pressure and heart problems, cautions NIH.
To reduce your risk of diseases such as cancer and heart disease (as well as keep your weight in check), he says, you need to eat a healthy diet that includes plenty of fruit, vegetables, and whole grains. You should also exercise and avoid smoking.
The bottom line: From what we know now, drinking a few cups of green tea a day is a perfectly healthy habit (as long as it's not loaded with sugar) and may have a few small benefits. But skip supplements. The evidence for any health boost is lacking, and there are potential risks.