When you drink too much coffee, the caffeine can increase stress levels which might lead to overeating. It can also promote insomnia, which might also lead to a higher consumption of calories. However, coffee contains other chemicals which stimulate the production of cortisone and adrenaline. These chemicals increase stress levels, and cortisone has been linked with an increase in abdomen fat, which causes morehealth concerns than fat in other areas.
Coffee itself has very few calories and no fat, but people rarely drink it without something added to modify the taste. Even a shot of flavored syrup can add calories to a coffee, and some of the more creamy and elaborate concoctions can have as many calories as an entire meal. Milk and cream are also very high in saturated fat, which not only contributes calories but is also dangerous for your health. Too much saturated fat can lead to heart disease.
The effects of coffee on weight loss don't seem to be enough to radically cause people to gain or lose weight. The best advice is to consume coffee in moderation if desired, and to be aware of the effects it has on you, in order to take advantage of them.