The study started out with nearly 20,000 trim middle-aged and older women. Over time, women who drank alcohol in moderation put on less weight and were less apt to become overweight compared to non-drinkers. This was true even after taking into account various lifestyle and dietary factors that might influence a woman's weight.
Red wine seemed best at keeping weight in check, but white wine, beer and spirits also had some benefit.
Our study results showed that middle-aged and older women who have normal body weight initially and consume light-to-moderate amount of alcohol could maintain their drinking habits without gaining more weight compared with similar women who did not drink any alcohol, Dr. Lu Wang from the division of preventive medicine, Brigham and Women's Hospital, Boston, noted in an email to Reuters Health.
Many prior studies have suggested that moderate drinking -- usually defined as a drink or two a day -- can be a healthy habit, particularly with regard to heart health, while heavy drinking can harm health.
The new study, published in the latest issue of Archives of Internal Medicine, is the first to examine ties between alcohol consumption by a normal-weight individual and the risk of becoming overweight or obese.
The women were all at least 39 years old when the study began. About 38 percent said they did not drink alcohol; 33 percent said they drank less than 5 grams daily (a standard drink has about 10 grams of alcohol); 20 percent drank 5 to less than 15 grams daily; 6 percent drank 15 to less than 30 grams daily; and 3 percent downed 30 grams of alcohol or more daily (about 2 to 3 drinks per day or more).
Over an average of about 13 years, the women generally gained weight. However, the teetotalers gained the most weight, with weight gain decreasing with increasing amount of alcohol consumed.
Women who did not drink gained an average of 3.63 kilograms (8 pounds) compared with 1.55 kilograms (3.4 pounds) for those who consumed 30 grams of alcohol or more each day.
During the 13 years the initially normal-weight women were followed, 41 percent became overweight or obese. Women who drank 15 to less than 30 grams per day had the lowest risk of becoming overweight or obese, which was 30 percent less than that of non-drinkers.
Put another way, Wang said an initially trim woman who did not drink alcohol had about a 43 percent chance of becoming overweight or obese over 13 years. Her risk fell to 33 percent if she drank 15 to 30 grams of alcohol a day.
Women who drank higher amounts of alcohol were generally more physically active, weighed slightly less at the outset and were more apt to be smokers, than other women. However, the association between drinking and less weight gain and risk of becoming overweight or obese remained strong after accounting for these factors. This suggests that alcohol may independently affect body weight beyond its relationship with diet and lifestyle factors.
There are several reasons why alcohol might help women stay trim, Wang told Reuters Health. In the current study, women consuming more alcohol ate less, particularly carbohydrates -- a finding seen in other studies. Moreover, it's been shown that women tend to expend more energy after drinking alcohol -- more so than that contained in the alcohol. Taken together, regular alcohol consumption in light-to-moderate amount may lead to a net energy loss among women, Wang said.