Green Tea: Sip Your Way to Fat Loss

Green Tea: Sip Your Way to Fat Loss

By Susan M. Kleiner, Ph.D., RD, FACN, CNS

How many times have you heard nutrition experts say there is no magic potion to help you lose weight? I wish I had a nickel for every time I’ve said the exact same thing. Fortunately, scientists continue to discover new things, and so do I. In fact, as I’m writing this, I am sipping on a steaming mug of what might possibly be a delicious elixir for fat loss. But, the science behind the claims leaves no trace of the magical art of illusion.

A Brief History of Tea

Tea is the most universally consumed beverage. It is prepared from the dried shoots of an evergreen shrub, Camellia sinensis. The Chinese believe that drinking tea promotes good health and longevity. Studies investigating tea and health have, in fact, linked tea drinking with positive health effects on cardiovascular diseases, cancer, insulin activity, bone mineral density, arthritis and even cataracts.1

Teas differ because of the way the leaves are treated before they are dried. For green tea, consumed largely in Asia, the fresh leaves are heated or steamed to inactivate enzymes before they are rolled and dried. For black tea, most popular in Western countries, the leaves are allowed to wither before they are rolled. Then they are held a few hours before being heated and dried. During the holding period, the enzymes catalyze chemical changes of certain tea constituents that result in changes in color, taste and aroma. Although black tea is described as “fermented,” the changes are due mainly to oxidation, rather than any bacterial process. Oolong tea is only partly or half fermented and a brew from Oolong tea has some of the characteristics of both green and black tea. Oolong tea is most popular in southeast China and Taiwan, and is often served in Chinese restaurants in the United States.2,3

Tea and Fat Loss

When we get down to the basics, there are two ways to lose weight: Eat fewer calories or burn more calories. Along with work by behavioral scientists trying to help people change their eating habits, nutrition scientists have been investigating how to alter the other side of the equation: energy expenditure and fat burning. This quest has led them to several extracts from plants that have thermogenic, or heat-generating properties, including caffeine from coffee and tea, ephedrine from ephedra, and capsaicin from pungent spices.

The thermogenic effect of tea has generally been attributed to its caffeine content. Studies show that it may not be the caffeine alone, but the interaction of other important compounds called catechin-polyphenols in the tea with caffeine that produces the greatest thermogenic effect, along with the added bonus of increased fat burning. Green tea is a particularly potent source of epigallocatechin gallate, one of the most bioactive catechin-polyphenols.

The Science

A number of research studies have documented increased energy expenditure and fat oxidation in humans and rats. Scientists in Switzerland studied whether a green tea extract in capsular form could increase energy expenditure and fat utilization in 10 men over a 24-hours period.4 The extract was designed to mimic a dose of green tea and contained a combination of 50 milligrams of caffeine and 90 milligrams of epigallocatechin gallate (EGCG) taken three times daily at breakfast, lunch and dinner. The effect of the green tea extract was compared to two other treatments taken in identical fashion: 50 milligrams of caffeine only, and a placebo. The green tea extract increased energy expenditure by four percent relative to the placebo treatment, or about 82 calories in 24 hours. Fat utilization was also increased. When compared to caffeine alone, there was still a three percent increase in energy expenditure, demonstrating an added or cooperative effect from the combination of caffeine with EGCG.

The researchers also examined the heart rates of the subjects because of the possible negative cardiovascular effects of caffeine. None of the subjects reported any side effects and no significant differences in heart rates across treatments were observed during the study.

A joint research project from the Human Nutrition Research Center in Beltsville, Maryland, with scientists from Japan, investigated the influence of oolong tea on metabolic rate and fat utilization in 12 men.5 This project examined four different supplement combinations: full-strength tea (daily dose: 270 milligrams caffeine, 244 milligrams EGCG); half-strength tea, water, plus caffeine (270 milligrams), and water alone. The tea was brewed at full strength by adding boiling distilled deionized water to a glass container containing the tea bags. The tea was steeped for 20 minutes and the bags were then removed. The subjects drank the treatments in 1.25-cup doses five times a day for four days. When compared to water alone, the full-strength tea increased energy expenditure by 70 calories and the water plus caffeine by 82 calories over 24 hours. Full-strength tea increased fat utilization by 12 percent and water plus caffeine increased fat utilization by eight percent when compared to water alone.

According to these researchers, there is likely a threshold dose response for caffeine above which there wouldn’t be any further increase in energy expenditure. In other words, the maximal response is reached with caffeine doses of 200-300 milligrams per day. Additional caffeine would not result in a greater response. As did the scientists in the previous study, these researchers speculated that there is a synergistic effect of the caffeine and the catechins that results in greater fat utilization than is seen with the effects of caffeine alone.

Another group of Maryland researchers have been investigating the influence of catechins on insulin activity.6 Reduced insulin sensitivity is one of the areas being investigated as a possible precursor or consequence of obesity. Enhancement of insulin sensitivity may help overweight individuals lose weight or manage body composition. In laboratory cell culture studies, tea was shown to increase insulin activity more than 15 times. Black, green and oolong teas, but not herbal teas, were shown to increase insulin activity. Addition of lemon to the tea did not affect the insulin-potentiating activity, but addition of one teaspoon of two percent milk per cup decreased the insulin-potentiating activity by one-third. When about one-quarter of a cup of milk was added to the cup of tea, the insulin-potentiating activity nearly disappeared. Nondairy creamers and soy milk also decreased the activity.

A study by Japanese researchers reported that tea catechins (600 milligrams per day) taken with the diet for 12 weeks in men promoted weight loss, a decrease in body mass index (BMI) and waist circumference compared to subjects consuming a placebo with a small amount of catechins.7 To begin to understand the actual mechanisms of exactly what is happening in the body and how the catechins work, these researchers conducted a  more recent study of the effects of tea catechins on energy and fat metabolism in rats.8 The rats were fed an extract of catechins from green tea with a minimal amount of caffeine. The study results clearly showed that the feeding of tea catechins helped suppress diet-induced obesity in the rats fed a high-fat diet. Since minimal caffeine was available in the tea extract, the effect was attributed primarily to the tea catechins, not caffeine. According to the researchers, the effects may be attributed in part to a stimulation of fat metabolism in the liver. Also, long-term tea consumption has the potential to influence body fat accumulation.

Tea, Please?

Although more research is needed, especially on women, it appears that the combination of catechin polyphenols and caffeine in tea may be a great way to help control body weight and possibly even lose weight. Even though 80 calories per day may seem like nothing (after all, its just a half a bagel), if you add up 80 calories per day for a year, that’s 29,200 calories, or almost 8.5 pounds! The studies that had positive results showed not only chronic tea consumption, but controlled calorie intake, too. Don’t think that a couple of cups of green tea are going to mask the effects of a pint of ice cream!

Most of the studies have been conducted using green tea, and secondly oolong tea, so right now these would be your teas of choice. The amount that you need to consume isn’t really clear yet. The 1999 study in Maryland used 6.25 cups of tea per day for four days. The more recent Japanese study on men found successful results feeding 2.5 cups every day for 12 weeks. If you are caffeine-sensitive, you might want to start with the lower dose, and definitely don’t drink the tea in the evening before bed. Cheers!


1. Yang CS, Landau JM Effects of tea consumption on nutrition and health. J Nutr 2000;130:2409-2412

2. ChineseTeas 101.

3. Charley, H. Food Science. Second Edition John Wiley and Sons, Inc, New York, NY 1982, p. 105

4. Dulloo AG, Duret C, Rohrer D, Girardier L, Mensi N, Fathi M, Chantre P, Vandermander J. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr 1999;70:1040-1045

5. Rumpler W, Seale J, Clevidence B, Judd J, Wiley E, Yamamoto S, Komatsu T, Sawaki T, Ishikura Y, Hosoda K. Oolong tea increases metabolic rate and fat oxidation in men. J Nutr 2001;131:2848-2852

6. Anderson RA, Polansky MM. Tea enhances insulin activity. J Agric Food Chem 2002; 50(24):7182-7186

7. Nagao T, Komine Y, Soga S, Otsuca K, Meguro S, Eatanabe H, Hase T, Tamaka Y, Tokimitsu I. Long-term intake of tea catechins reduces body fat in men. Int J Obes Relat Metab Disord 2002;26:S158

8. Murase, Nagasawa A, Suzuki J, Hase T, Tokimitsu I. Beneficial effects of tea catechins on diet-induced obesity: stimulation of lipid catabolism in the liver. Int J Obesity 2002;26:1459-1464

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