Green TeaApril 2007
By David Nayor
Scientific research on the health benefits of green tea is expanding exponentially, with more than 1,500 articles published in prestigious journals over the last five years alone.
While green tea’s medicinal properties have been described for more than 1,000 years, one of its most timely benefits may be supporting weight management by increasing metabolism and promoting fat burning. With nearly two thirds of the American population now overweight or obese—and thus at heightened risk for metabolic syndrome, heart disease, cancer, and other life-threatening ailments—effective weight-control strategies are fast becoming a matter of life and death.
In addition to promoting healthy body weight and composition, green tea may help ward off numerous health conditions that afflict aging adults, from cataracts to autoimmune disorders. Green tea’s health-promoting properties have even been recognized by the FDA, which recently approved the first prescription drug derived from green tea.
In this article, we examine compelling research supporting green tea’s role in helping to achieve and maintain a healthy body weight, along with myriad studies testifying to its broad-spectrum effects in promoting optimal health and well-being.
Green Tea Supports Healthy Body Mass and Composition
America’s looming obesity epidemic has spurred scientists to seek new agents that promote healthy body weight and composition. Certain spicy foods and herbal drinks have long been used as weight-management tools because of their purported ability to promote thermogenesis or satiety. Scientists have proposed that such agents—like ginger and black pepper—may help prevent excessive weight gain and obesity via these mechanisms.1
During the past decade, green tea has received particular attention for its role in promoting healthy weight management. Its weight-control effects have been studied extensively in cell, animal, and human studies. Laboratory and animal models suggest that green tea, green tea polyphenols known as catechins, and green tea’s principal catechin, EGCG, may work to promote healthy weight management by:
At the same time, green tea has been found to increase the oxidation (breakdown) of fats. Human studies suggest that green tea consumption is associated with decreased body mass and body fat.2
Green Tea Promotes Thermogenesis
Earlier research suggested that caffeine in green tea might be responsible for its thermogenic effect. Later studies, however, reported that green tea’s thermogenic effects were too great to be attributed to caffeine alone. Instead, scientists proposed that green tea polyphenols may work in synergy with caffeine to promote thermogenesis.8
According to recent findings, EGCG may be an important contributor to green tea’s effects in promoting thermogenesis and healthy weight control. Scientists believe EGCG works by inhibiting catechol-O-methyltransferase, an enzyme that degrades norepinephrine. Produced by the adrenal glands in response to stress, the hormone norepinephrine increases metabolic rate, which likely contributes to green tea’s effects on thermogenesis.9
Green Tea Inhibits Fat Digestion and Absorption
Several years ago, scientists suggested a possible mechanism by which green tea may guard against excess body weight. In the laboratory, scientists found that a green tea extract inhibited fat-digesting lipase enzymes of the stomach and pancreas. By inhibiting fat-digesting enzymes, green tea likely reduces fat digestion in humans, thus averting some of the dangers of consuming excess fat calories.10
A recent human study provides support for these earlier findings. In a trial published last year in the European Journal of Clinical Nutrition, researchers found that polyphenol-enriched oolong tea (a partially fermented cousin of green tea) helps promote the fecal excretion of lipids following consumption of fatty foods. In a well-designed study, 12 healthy adults consumed a large quantity of fat from potato chips twice daily, along with either a placebo drink or polyphenol-rich tea three times daily. Tea consumption led to an increased fecal excretion of dietary fats, suggesting that tea polyphenols guard against the dangers of excessive dietary fat absorption.11 Based on this study, it might be prudent to take two high-potency green tea capsules, or drink several cups of green tea with fatty meals.
Green Tea Promotes Fat Burning, Supports Healthy Body Weight
An animal study provides important clues to green tea’s effects on body weight. Scientists fed mice a high-fat diet in order to induce obesity, and then supplemented the mice with EGCG and monitored biochemical and metabolic changes in the animals. EGCG helped reduce the accumulation of additional body fat, even though food intake remained unchanged. Furthermore, the EGCG-supplemented mice displayed metabolic changes suggestive of increased fat burning. Dietary EGCG consumption thus reduced the gain of fat mass. This may have resulted from increased fat burning, reduced digestibility of dietary fats, or a combination of factors.12
Green Tea Boosts Exercise Capacity
Another animal study suggests that green tea may enhance exercise endurance and fat-burning ability. Scientists noted that when mice were supplemented with green tea extract, their exercise capacity increased substantially. In fact, compared to a control group of animals, mice supplemented with green tea ran 30% longer before becoming exhausted. Additionally, the supplemented mice displayed markers of increased fat oxidation. These findings suggest that green tea improved exercise endurance by increasing the utilization of fatty acids as an energy source during exercise.13
Human Studies Confirm Green Tea’s Effects
Additional human studies support green tea’s ability to boost metabolism and support healthy weight management.
A study published in the American Journal of Clinical Nutrition found that green tea extract significantly increased energy expenditure (a measure of metabolism) in adults, while also boosting fat burning. When men supplemented with 90 mg of EGCG and 50 mg of caffeine three times daily, their 24-hour energy expenditure increased by 4%. The supplemented men thus burned 79 more calories a day than men who did not supplement. The increase in energy expenditure came from burning fat, as opposed to a breakdown of protein (muscle) mass. These important findings suggest that green tea extract can be an important tool in maintaining healthy body weight and composition.14
Another study lends support to green tea’s role in healthy weight control in humans. In this trial, moderately obese adults supplemented with a green tea extract. After three months, they demonstrated a 4.6% decrease in body weight and a 4.5% decrease in waist circumference. This important study demonstrates that green tea effectively supports healthy body mass and protects against dangerous excess weight around the abdomen, which is a potent risk factor for metabolic syndrome.15