Our bodies eliminate alcohol by breaking it down in a series of chemical reactions and using the energy freed by those reactions. Alcohol’s chemical structure has similarities to both sugar and fat, and it has a nutritional value between the two, around 7 calories per gram (sugar has 4 calories per gram, fat 9). It provides around 5% of the calories in the American diet, much more among heavy drinkers.
Alcohol is broken down and converted into energy in two organs, the stomach and the liver. The “first-pass” metabolism of alcohol in the stomach consumes a portion before it gets to the small intestine and then into the blood. That portion is around 30% in men, but only 10% in women. Men therefore experience a slower rise in blood alcohol when they drink, and can drink more before they feel its effects. And there are strong genetic influences on how well individuals are able to handle alcohol.