Caffeine, which is found in coffee, stimulates the nervous system, which sends direct signals to the fat cells to tell them to break down fat.
Another thing that caffeine does is to increase our blood levels of the hormone Epinephrine, which is also known as Adrenaline. Epinephrine travels through the blood, to the fat tissues and send signals to break down fats and release them into the blood.
This is how caffeine helps to mobilize fat from the fat tissues, making it available for use as free fatty acids in the blood. How many calories we burn at rest is called the Resting Metabolic Rate (RMR). The higher our metabolic rate, the easier it is for us to lose weight and the more we can allow ourselves to eat without gaining.
Studies show that caffeine can increase the metabolic rate by 3-11%, with larger doses having an even bigger effect. Interestingly, most of the increase in metabolism is caused by an increase in the burning of fat.