How does tea help to reduce weight?

The major components responsible for the anti-obesity and hypo-lipidemic (lowering blood fat level) effects in teas are catechins, caffeine, and theanine. 

These reduce body weight through following mechanisms:

• Suppress the fatty-acid synthesis gene (The gene responsible for fat forming enzyme production).
• Stimulate cell energy expenditure.
• Reduce food intake and food efficiency.
• Increase fat oxidation.