The relation between alcohol consumption and body weight is still basically a mystery to us. The epidemiologic evidence is inconsistent, with many studies suggesting no or very little weight gain in men and the opposite in women. Some studies have shown that moderate amounts of alcohol are good for you.
Alcohol contains 7 kilocaories per gram, which is almost as much as fat. However, this energy cannot be stored and is simply metabolized until the alcohol has been cleared out of your sysem. If alcohol can cause weight gain, I assume the problem arises from what happens after your body has used up the alcohol and has food in it and little need for energy.
Of course, all of the above is interesting information but what's relevant is that beer bellies are in my opinion simply the result of poor diet and exercise habits. Drinking in moderation is not going to throw your body's metabolism out of balance. Heavy drinking, on the other hand, is noted for having many detrimental affects on your health.