Your body has a set number of calories that is needed to maintain your weight. This need is based on your height, weight, age, gender, as well as activity level. When you take in more calories than what your body requires, you will gain weight. Alcohol can lead to weight gain from the calories it provides and also by causing you to eat more calories after consuming the alcohol.
Research has shown a 20% increase in calories consumed at a meal when alcohol was consumed before the meal. There was a total caloric increase of 33% when the calories from the alcohol were added. Along with the increase in weight you can have an increased risk to your health because of where you gain the weight. A study of over 3 000 people showed that consuming elevated amounts of alcohol is associated with abdominal obesity in men. Many people joke about this being a “beer belly.” Unfortunately, a “beer belly” puts you at an increased risk for type 2 diabetes, hypertension, and cardiovascular disease.
Studies also show that in the short term, alcohol stimulates food intake and can also increase feelings of hunger. Having your judgement impaired and stimulating your appetite is a recipe for failure if you are trying to follow a weight-loss plan.
Try reducing calories when consuming alcohol in the following ways:

Source: www.medicinenet.com