Green Tea for Weight Loss
By Jay Udani, MD, and Myles Spar, MD, MPH
There has been growing interest in the use of green tea and green tea extracts to promote weight loss. As concern with adverse effects from ephedra products grows, more and more consumers are looking for alternative natural supplements to assist with weight loss. Green tea may be the best alternative.
Obesity is a significant health problem in the United States. According to the Surgeon General’s Report on Overweight and Obesity, 61% of American adults were overweight in 1999;1 even more recently, 33% of adult females and 28% of adult males in the United States were estimated to be obese. The annual revenue for the dieting industry is estimated to be more than $30 billion.2
Tea is second only to water as the world’s most popular beverage. Such popularity of tea has been demonstrated in Asia for millennia, and the demand for this important beverage has been growing in the West, as its health benefits, ranging from cancer prevention—with potential for the inhibition of angiogenesis—to cholesterol lowering, have become more widely known.
All tea is picked from a leafy green shrub in the same family as Camellia plants (Camellia sinensis). Only the most tender new leaves are picked for tea. If black tea is made, the new leaves are allowed to ferment and cure, thus oxidizing. This process adds flavor to the tea, but it also allows chemicals in the leaves to break down some of the active chemicals in the tea, such as the polyphenols, which appear to be responsible for green tea’s many health effects. Black tea, therefore, may lack many of the health benefits that will be discussed in relation to green tea.
Green tea is prepared by lightly steaming the leaves after picking. This steaming preserves the polyphenols and prevents fermentation, destroying the enzymes that would break down the active compounds in the leaf and cause them to oxidize, thus preserving the activity of the polyphenols.
Chemically, green tea functions as an antioxidant because of its particular types of polyphenols, known as catechins, which are up to eight times more powerful as antioxidants than vitamin C, as measured by total radical scavenging activity.3 Antioxidants promote health by repairing or preventing damage caused by chemicals that generate free radicals; green tea polyphenols have been shown to be antimutagenic in vitro.
Green tea extract has been shown to inhibit breast cancer cell proliferation in vitro and in mouse models, perhaps by inhibiting angiogenesis.
Other Health Effects
Traditional Chinese medicine uses green tea to facilitate digestion, stabilize body temperature, and enhance mental function. Ayurvedic medicine employs green tea as an astringent, stimulant, and diuretic.
In humans, epidemiologic studies have shown chemoprotective effects of green tea. One study in Japan showed that increased consumption of green tea was associated with a decreased risk of developing adeno-matous polyps of the sigmoid colon. Green tea also has been shown to decrease cholesterol and triglyceride levels.4 Green tea also may decrease the occurrence of thromboembolism by inhibiting platelet aggregation.1
Mechanism of Action
It has been shown in vitro that the catechins in green tea can inhibit an important enzyme, catechol-O-methyl transferase (COMT), which normally causes a decrease in the amount of thermogenesis within adipose tissue. Because COMT degrades norepinephrine, it is thought that by inhibiting the action of COMT, green tea catechins allow for a prolonged effect of norepinephrine on thermogenesis and fat metabolism.
Green tea extracts also have been shown to inhibit lipolysis. Lipolysis is the process by which dietary fats (triglycerides) are broken down by gastric and pancreatic lipases so that the resultant fatty acids can be absorbed in the small intestine. Inhibition of the breakdown of triglycerides prevents absorption of the fat, therefore, in theory, promoting less weight gain.
Studies have investigated the ability of green tea and green tea extract to stimulate thermogenesis and to inhibit triglyceride metabolism. Because green tea contains caffeine and caffeine is known to promote thermogenesis, several studies have been carried out to show the effects of the green tea catechin polyphenols.
In one study done on brown fat cells in vitro, it was shown that the catechins in the green tea extract worked much more strongly than caffeine alone. In fact, synergistic work with caffeine was observed: Caffeine had a similar effect to the catechins in inducing thermogenesis.5 The effect was equal to or greater than an ephedrine-caffeine combination.6
In vitro studies have demonstrated a dose-dependent inhibition of lipolysis through inhibition of the gastric and pancreatic lipases by green tea extract. When these studies were replicated in conditions more similar to the human body, the results were less striking.7
A group from the University of Geneva compared green tea extract (containing 1,500 mg extract with 270 mg epigallocatechin and 150 mg caffeine) vs. caffeine (150 mg) vs. placebo in a double-blind three-arm study among 10 healthy men.8 The green tea extract group had a significant increase in energy expenditure and fat oxidation over both of the other two arms. The tea group did show somewhat greater inhibition of carbohydrate oxidation. This means that the extract helped increase fat metabolism, contributing to a higher energy expenditure, but caused a decrease in carbohydrate metabolism. The decreased metabolism of carbohydrates reduced the energy expenditure, but the net change was still in favor of increased energy expenditure. The extract used was an alcohol extract of dried green leaves containing 8.35% caffeine and 24.7% catechins.
A French group performed a double-blind randomized study of green tea powder vs. placebo in 60 obese women.9 The green tea group exhibited significantly greater weight loss and decrease in waist circumference at 15 and 30 days. The amount of catechins was not specified, but the formula used included 250 mg whole tea powder in the form of green tea "Arkocaps." No side effects were mentioned when subjects were asked by investigators; no withdrawals or drop-outs were reported.
A more recent study was published using a newer version of the same formulation.10 The green tea extract used was AR25, which contains 25% catechins. This study referenced older work showing that the extract inhibited gastric and pancreatic lipases and increased thermogenesis in vitro. This clinical trial showed a decrease in weight by 4.6% and waist circumference by 4.5% after three months of AR25 use.
The normal adult consumption of tea in Japan is 2-3 cups per day with an average of 60 mg of polyphenols per cup. Because green tea can seem bland to the American consumer used to the strong taste of black tea, marketers are producing green tea in a variety of flavors. These flavorings, if natural, appear to do nothing to decrease the health benefits of the tea and may make it easier for the average consumer to drink.
Despite the great increase in tea choices available, people will look for the increased convenience and stronger effects found in encapsulated forms. Available products usually are standardized to the total polyphenol content (60-97% total polyphenols) or to epigallocatechin gallate, the most powerful antioxidant in green tea. Decaffeinated products are recommended because in this form, green tea extract would provide a very high dose of caffeine. A dose of approximately 250 mg of polyphenols was used most often in clinical studies.
The polyphenols themselves in green tea have not been associated with any significant side effects or toxicity. There is evidence that condensed polyphenolic compounds in the form of flavonoids (catechins or tannins) of tea is linked to a high rate of esophageal cancer in regions of heavy tea consumption. A high tannin concentration in tea may be overcome by adding milk, which binds the tannin, possibly preventing its detrimental effects.11 Other adverse effects that have been mentioned include gastrointestinal upset and constipation.12 There also has been reported an association of microcytic anemia among infants with the intake of more than 250 mL/d.13
An average six-ounce cup of green tea will have from 10-60 mg of caffeine. Caffeine is a central nervous stimulant that can induce nervousness, insomnia, tachy- cardia, elevated blood sugar and cholesterol levels, and high levels of stomach acid and heartburn. Although this amount of caffeine is much less than is present in black tea or coffee, caffeine-sensitive individuals or those drinking a large amount of tea can see some of the negative effects of too much caffeine. These also could include jitteriness, tremor, and increased anxiety. For those people, a decaffeinated green tea is best.
Supplements containing concentrates of green tea that are not decaffeinated would contain large amounts of caffeine, which could lead to similar symptoms.
Although larger randomized controlled trials are needed, the few studies that have been done suggest that green tea may be a safe and effective alternative to ephedra for stimulating thermogenesis for weight loss. Further studies will require a longer evaluation of green tea to determine if the effect of green tea catechins is attenuated with time.
Preliminary in vitro and animal data also show promise for green tea’s ability to inhibit lipolysis. Although this could be advantageous in terms of weight-loss promotion, it also could cause a decrease in the absorption of important omega-3 fatty acids and fat-soluble vitamins. Clinical trials in humans are needed for further clarification of green tea’s role and its relationship to this mechanism of weight loss.
Decaffeinated green tea extracts have begun to demonstrate efficacy with minimal side effects; therefore, with more supporting research, this product could be useful as an adjunct to a weight-loss program. It is recommended that the consumer look for products listing the total polyphenol or catechin content. The clinical studies mentioned in this article used at least 250 mg of active catechins per day. Thus, it would be advisable to use an equivalent amount. Of course, the use of green tea or green tea extract must be incorporated into a more comprehensive weight-loss program that includes exercise and proper diet.
Dr. Udani and Dr. Spar are Clinical Instructors, University of California Los Angeles School of Medicine; Dr. Udani also is Medical Director, Northridge Hospital Integrative Medicine Program, Northridge, CA.
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