When people go on a diet, they often choose the "light" version of their favorite alcoholic beverages in order to save a few calories. However, that is only a small piece of the puzzle. Fat metabolism is reduced by as much as 73% after only two alcoholic beverages. This scary fact shows that the primary effect of alcohol on the body is not so much how many calories we consume, but how it stops the body's ability to use your fat stores for energy.
Alcohol in the body is converted into a substance called acetate. Unlike a car that uses one supply of fuel, the body is able to draw from carbohydrates, fats and proteins for energy. When your blood acetate levels increase, your body uses acetate instead of fat. To make matters worse, the more you drink the more you tend to eat; and unfortunately, drinking will make your liver work to convert the alcohol into acetate, which means that the foods you consume at this time will be converted into extra fat on your body.
If that didn't sound bad enough; alcohol stimulates appetite and decrease your testosterone levels for up to 24 hours and increases estrogen by 300%. The infamous "beer belly" is really just an "estrogen belly." Biochemically, the higher your level of estrogen is, the more readily you absorb alcohol, but the slower you break it down.
Muscle Tip: Drinking alcohol is the most efficient way to slash your testosterone levels; women...we don't want this to happen either. Just a single event of serious drinking raises levels of the muscle-wasting stress hormone called cortisol and decreases the levels of testosterone for up to 24 hours. If you are working out to build strong fat-burning muscles yet consuming alcohol, this actually breaks down muscle further and you end up with a slower metabolism. This is because you break down muscle as you lift weights and you repair them as you rest if you have proper hormone levels...if not, you never repair your muscles properly!
Also, we all know that alcohol dehydrates us. In order for fat to be metabolized, it must first be released from the fat cell and then be transported by the bloodstream where it is pushed to the liver to be used as fuel. If you are dehydrated, the liver has to come to the aid of the kidneys and can't focus on its role of releasing fat.
Alcohol also affects every organ of the body; it's most dramatic impact is upon the liver. The liver cells normally prefer fatty acids as fuel, and package excess fatty acids as triglycerides, which they then route to other tissues of the body. However, when alcohol is present, the liver cells are forced to first metabolize the alcohol, letting the fatty acids accumulate in huge amounts. Alcohol metabolism permanently changes liver cell structure, which impairs the liver's ability to metabolize fats, which causes fatty liver disease. To read more, check out this book: Secrets to a Healthy Metabolism. It has a whole chapter called "Alcohol, It's Not Just the Calories!"