Caffeine is a stimulant that is often used by dieters because it increases thermogenesis (heat generation due to the bodies metabolism). Studies suggest that moderate caffeine intake can increase daily calorie expenditure by more than 100 calories a day.

One study, published in the American Journal of Clinical Nutrition, looked at the effect of caffeine on total energy expenditure in a group of lean and obese women. The researchers found that 100mg of caffeine increased energy output by 3 to 4% over a 150 minute period. When the caffeine was administered at two hour intervals during a 12 hour period, total energy intake was increased by 12% in the lean group and 8% in the obese group.

The benefits of green tea on weight loss have been borne out through several scientific studies.

One such study, published in the journal Obesity in 2007 looked at the relationship between consumption of green tea extract and weight in a group of 240 Japanese women. The women were divided into two groups, a control group which received 96mg of green tea catechins a day, and a test group which received 583mg of green tea catechins a day.