Is alcohol consumption a risk factor for weight gain and obesity?

Alcohol represents an important source of energy. Despite its comparatively high energy content of 7.1 g/kcal, it is still controversial whether moderate amounts of alcohol represent a risk factor for weight gain and obesity. Epidemiologic data showed a positive, negative, or no relationship between alcohol intake and body weight. Despite the difficulty in assessing alcohol intake as well as controlling for different confounders of the energy-balance equation, the conflicting epidemiologic data can be explained in most instances. Every component of the energy-balance equation is affected by the ingestion of alcohol. Moderate amounts of alcohol enhance energy intake due to the caloric content of the alcohol as well as its appetite-enhancing effects. Alcohol-induced thermogenesis is approximately 20% in healthy nonalcoholic subjects, i.e., moderate alcohol consumers, which is higher than for other energy substrates but considerably lower than in heavy alcohol consumers. This would suggest that a major fraction of the alcohol energy represents a navailable energy source for ATP synthesis in moderate non-daily alcohol consumers. Experimental evidence from several metabolic studies showed a suppression of lipid oxidation by alcohol and thus the enhancement of a positive fat balance. The nonoxidized fat is preferentially deposited in the abdominal area. The experimental metabolic evidence suggests that the consumption of moderate amounts of alcohol has to be accounted for in the energy-balance equation and may represent a risk factor for the development of a positive energy balance and thus weight gain. In the heavy alcohol consumer and eventually also in daily moderate alcohol consumers, a larger fraction of the alcohol energy might not be an available source of energy due to the induction of the microsomal ethanol-oxidizing system (MEOS). Experimental data in combination with epidemiologic findings suggest that alcohol energy counts more in moderate nondaily alcohol consumers than in some moderate daily and all heavy consumers. Accordingly the question is not "Whether alcohol calories do count" but "How much do alcohol calories count?". There seems to be a large individual variability according to the absolute amount of alcohol consumed, the drinking frequency as well as genetic factors. Presently it can be said that alcohol calories count more in moderate nondaily consumers than in daily (heavy) consumers. Further, they count more in combination with a high-fat diet and in overweight and obese subjects.