The most famous study linking Oolong tea with weight loss was published in August of 2003. Researchers at the University of Tokushima School of Medicine and seven other schools found that oolong tea increased the burning of calories by 10%, while women drinking green tea had an metabolic increase of 4%. Both teas increased the burning of fat when drunk after a meal, but Oolong tea appeared to do a better job.

Another Japanese study was done in 2006, and researchers found that oolong tea was able to reduce the absorption of fats eaten during a meal. They found that lipids (fats) were passed through the body in the stool at a higher rate than participants who did not drink the tea after their meals. The tea also had a positive effect on the participant's cholesterol levels.

Green tea has been used traditionally in Japan and other Asian countries by women who wish to stay thin. Green tea has also been used as a cancer-preventative.

Green tea, oolong (or wu-long) tea, and black tea all come from the same plant. The differences in the finished product that we drink comes from the differences in how long the three types of tea are processed and fermented. Green tea has been processed the least, and black tea has been processed the most. Oolong tea falls in the middle.

Oolong tea contains about half the caffeine as green tea, but more polymerized polyphenols, the chemical that is thought to increase the metabolism of fats. Although caffeine can increase the metabolism, to some extent, it is evidently not caffeine that makes oolong tea more efficient as a weight loss drink.