Women who drink once in a while may have an easier time staying slim than women who do not drink at all, according to a recent US study.

Women who drank red wine gained the least weight overall, and some of the women who did not drink went on to become overweight or obese 12 years after the study began.

All in all, women who drank between one and two glasses of beer, wine, or spirits a day were up to 30% less likely than teetotallers to become overweight or obese.

Researchers said that women who already drank in moderation should be encouraged by the finding, but that people should not take up drinking in order to lose weight.

For the study, researchers originally quizzed more than 19,000 women, all older than 39, none of whom were overweight or obese when the study began.

In the initial questionnaire, some 40% of the women reported not drinking at all, 33% said that they had about two drinks a week, 20% said they had about one drink a day, 6% said two drinks a day, and 3% drank more than two drinks a day.

When the researchers polled each of the women a second time, after an average of 13 years, they found that most of the women had gained some weight.

Even when the researchers adjusted their calculations for age differences, race, total calorie intake, activity level, and tobacco use, they found that the women in the study who did not drink at all were the most likely to gain weight.

Other studies have linked moderate alcohol use to limiting weight gain.

In a large health survey done in 2005, researchers found that people of both sexes who drank in moderation were thinner, on average.

Binge drinking was associated with increased obesity risk, however.

Ahmed A. Arif, an associate professor of epidemiology at the University of North Carolina in the US, who led the study from several years ago, said that he did not know what biological mechanisms might make people who drink moderately less likely to be obese.

The researchers who worked on the present study said that they believed women who drank alcohol substituted alcohol calories for food calories when they drank.

Catherine Collins, a dietitian and spokesperson for the British Dietetic Association, said that she believed it would be a mistake to think that drinking alcohol helped people lose weight.

She said that the women who took part in the recent study were not average, and that being within a normal weight range by age 39 was quite a feat in itself.