Based on the fact that energy content in 1 gram of alcohol is 29 kJ or 7.1 kcal, alcohol consumption can lead to weight gain. The present review was conducted to analyze the effects of alcohol consumption on body weight. A search of the Medline database for the period 1984 to March 2010 was conducted to identify cross-sectional, prospective cohort studies and intervention trials investigating the relationship between alcohol consumption and the risk of weight gain. Thirty-one publications were selected on the basis of relevance and quality of design and methods. The findings from large cross-sectional studies as well as from well-powered, prospective, cohort studies with long periods of follow-up were contradictory. Findings from short-term experimental trials also did not show a clear trend. The overall results do not conclusively confirm a positive association between alcohol consumption and weight gain; however, positive findings between alcohol intake and weight gain have been reported, mainly from studies with data on higher levels of drinking. It is, therefore, possible that heavy drinkers may experience such an effect more commonly than light drinkers. Moreover, light-to-moderate alcohol intake, especially wine intake, may be more likely to protect against weight gain, whereas consumption of spirits has been positively associated with weight gain. Further research should be directed towards assessing the specific roles of different types of alcoholic beverages. Studies should also take the effect of consumption patterns into account. In addition, a potential effect modifier that has not been evaluated before but might be important to consider is the subjects' previous tendency to gain weight.