Alcohol technically has 7 calories per gram but alcohol isn't metabolized by the body efficiently the way food is. While a shot of vodka technically has 100 calories if you measure it in a bomb calorimeter, your body sends it to the liver and tries to get rid of it rather than use it for energy. Alcoholics and drinkers often do gain weight but it's more from the fact that actual drinks usually also have sugar or carbs and not just ethanol itself, plus the fact that people typically eat greasy unhealthy food when drunk.