Oolong tea has been traditionally consumed in East Asia, but its use for weight loss is primarily supported by scientific findings rather than cultural tradition. Several small-scale clinical studies and animal experiments suggest that oolong tea may help reduce body weight and fat accumulation. The mechanisms proposed include the stimulation of energy expenditure, enhancement of lipid metabolism, and inhibition of fat absorption, largely attributed to its caffeine and polyphenol content (especially catechins and theaflavins).

A few randomized controlled trials have shown that regular consumption of oolong tea can increase energy expenditure and fat oxidation in humans. For example, a study published in the Chinese Journal of Integrative Medicine (2009) found that overweight and obese subjects who consumed oolong tea for six weeks experienced modest reductions in body weight and body fat. Another study in The Journal of Nutrition (2001) suggested that oolong tea increases energy expenditure compared with water or green tea.

However, the magnitude of the effects observed is generally small, and the quality of evidence is limited due to short study durations and small sample sizes. Systematic reviews conclude that while oolong tea may have a modest effect on weight loss, more rigorous, large-scale clinical trials are needed to substantiate these findings. Thus, the evidence is rated as moderate to low (2/5).