Here’s a new diet drink to help people shed pounds: oolong tea enriched with some of the antioxidant compounds that naturally occur in green tea. Men who drank this hybrid brew during a 3-month study in Japan lost 1.1 more kilograms in weight than did men drinking conventional oolong tea—with no other difference in their respective diets or exercise.

GO ON GREEN. Green tea is richer than other brews in catechins, so it’s used to make a fortified brew being tested in dietary studies. S. Ausmus/USDA-ARS
TEA TIME. Even before a long-term human trial confirmed the weight-reducing attributes of tea catechins, Kao Corp. began marketing this heavily fortified diet aid—with the Japanese government’s approval. Kao Corp.

The hybrid tea also offered a second benefit: reduced development of oxidized fatty materials in the bloodstream, such as low-density-lipoprotein (LDL) cholesterol, the bad cholesterol. Oxidized fats, especially LDL cholesterol, have been linked to the formation of artery-clogging plaque and heart attacks.

Indeed, Tomonori Nagao and his collaborators conclude, these results suggest a possible role for the chemical process of oxidation in the accumulation of body fat.

Why green tea?

This is not the first study to suggest a slimming effect of green tea. Five years ago, European scientists reported that 10 men in one study burned more calories on a day during which they took two capsules containing epigallocatechin gallate (EGCG), a compound that develops in most brewed teas and especially in green tea (SN: 1/1/00, p. 11).

The amount of extra energy burned on the day when the EGCG capsules were consumed was small, only 80 calories. Moreover, the test lasted a mere 3 days: One when the recruits got caffeine, another when they received the amount of EGCG typically present in 2 to 3 cups of green tea, and a day when they downed placebo capsules. Still, the findings were an important spur to the health-foods industry to deliver green tea extract or EGCG itself to weight-conscious consumers.

Bolstering the enthusiasm for green-tea components as a diet booster was work done by scientists at the world’s largest agricultural-science facility, the federal government’s Beltsville (Md.) Agricultural Research Center. There, a study in 12 men indicated that some component of tea other than caffeine prompted the body to use fat to fuel its energy needs. Each volunteer burned about 12 percent more fat on days when he drank full-strength oolong tea than on days he drank caffeine-laced water.

The green-tea agents suspected of boosting an individual’s calorie-burning rate, or metabolism, are catechins, chemicals in the flavonoid family. Many dietary flavonoids, such as the anthocyanins in berries, have turned out to be potent antioxidants. Catechins tend to be found in woody plants, such as Camellia sinensis, the shrub whose leaves are used to make true teas—as opposed to herbal teas (see Another Green That Might Prevent Breast Cancer). Which catechins predominate in any given tea depends on how the plant’s leaves were processed—for green, oolong, or black tea (see A Brew for Teeth—And the Rest of You).

The experimental brew

For their new trial, Nagao and his colleagues at Kao Corp. in Tokyo decided to investigate whether catechins’ apparent calorie-burning benefit in green teas could be maintained for several months. So, the scientists recruited 38 company employees to drink tea as prescribed and have their weight monitored.

All received a 340-milliliter bottle (roughly two teacups worth) of oolong tea, which is Japan’s favorite, to drink with dinner each day. Half of the men got oolong laced with some 22 milligrams of green-tea catechins. The rest drank tea spiked with 690 mg of the catechins. A typical serving of green tea can contain anywhere from 20 to 50 mg of catechins, depending on the brand and how it was brewed, Nagao says. The recipes of both experimental teas were adjusted to deliver identical concentrations of caffeine. Until the trial was completed, neither the participants nor the overseeing scientists knew which brew a recruit had been assigned to receive.

Because none of the recruits was slim, the researchers computed how many daily calories were needed to maintain each participant’s weight and then assigned each man to eat 10 percent fewer calories than that. So, all men who followed the dietary guidance should have lost some weight during the 12-week trial. On workdays, the men ate meals individually prepared for them and served in the company cafeteria. When they had to eat at home—principally on holidays and weekends—the recruits were told to adhere to eating tips that would roughly match the cafeteria dining. All food consumption was recorded. Throughout the trial, caffeinated and catechin-rich foods other than the teas were limited.

Big fat target

In the January American Journal of Clinical Nutrition, Nagao’s team reports that both groups of men lost weight—roughly 1.3 kilograms for those drinking the low-catechins tea and 2.4 kg for those on the brew heavily spiked with catechins.

More importantly, much of the weight loss in the latter group came from fat. Compared with measurements of the men before the trial began, total fat volume fell 10.3 percent in the average high-catechin-tea drinker but just 2.6 percent in the others. Further analysis showed that roughly equal proportions of subcutaneous fat (stored in pads under the skin) and visceral fat (the marbling within muscle and internal padding deep within the trunk) disappeared in both groups. That’s good because although paring subcutaneous fat leads to a slimmer physique, losing visceral fat is better for a person’s health. Visceral fat poses a greater risk of heart disease and diabetes (SN: 6/19/04, p. 388).

Visceral fat also contributes to a bigger belly, and not surprisingly, both groups found their belts loosening during the trial. The low-catechin tea drinkers shaved 1.6 centimeters off their waistlines while the high-catechin group trimmed off more than twice that much.

Similar advantages from the high-catechin tea emerged in the researchers’ analysis of fatty particles in the men’s blood. For instance, while concentrations of triglycerides—which increase a person’s risk of heart disease—increased a little more than 2 percent in the low-catechin group, they remained unchanged in the high-catechin-tea drinkers. And although cholesterol concentrations increased in both groups of men, it climbed 6.3 percent in the low-catechin group but only 3.4 percent in the others. Moreover, concentrations of dangerous LDL cholesterol and oxidized-LDL cholesterol dropped in both groups, but more than three times as much—11.5 percent and 36.3 percent, respectively—in the men who drank the high-catechin brews.

The oxidized LDL changes were particularly encouraging, the researchers note, citing studies indicating “that an increase in plasma [oxidized]-LDL can be used as a marker of unstable atherosclerotic cardiovascular disease.” Nagao says his company is now moving toward longer-term and larger trials of tea drinking among men and women.

In the meantime, if adherence to a New Year’s resolution to drop the pounds is waning—as it does in most people by the end of January—then maybe it’s time to consider switching one’s caffeinated pick-me-up to green tea.

Consumers in Japan have an additional specially-fortified choice: a Kao Corp. green tea that packs 540 mg of these chemicals into each 350 ml bottle. Indeed, the Japanese government has approved a product-labeling claim for this nutraceutical, or food with potential health benefits (see The Rise of Nutraceuticals). It reads: “Due to its high content of tea catechin, this green tea is suitable for people concerned about body fat.”

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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