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.
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
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