A small glass of red wine contains about 130 calories and nearly 16 grams of alcohol. (Francois Mori/Associated Press)

Women younger than 50 who drink light to moderate amounts of alcohol appeared to gain less weight during a 13-year study, according to U.S. research that adds to the conflicting messages about the effects of alcohol on health.

In Monday's issue of the Archives of Internal Medicine, researchers reported their results on alcohol consumption and weight gain.

Dr. Lu Wang of Brigham and Women's Hospital in Boston and her colleagues surveyed 19,220 U.S. women age 39 or older who had a body mass index in the range classified as normal (18.5 to 25). Participants were asked to recall how many alcoholic beverages they typically drank per day in the previous year and to report their weights. Relying on self-reported data and participants' recall were limitations of the study.

The researchers found:

• 7,346 women (38.2 per cent) reported drinking no alcohol.
• 6,312 (32.8 per cent) drank less than five grams.
• 3,865 (20.1 per cent) drank between 5 and 15 grams.
• 1,129 (5.9 per cent) drank between 15 and 30 grams.
• 568 (3.0 per cent) drank 30 grams per day or more.

A small glass of wine contains about 130 calories and nearly 15 grams of alcohol, while a bottle of beer contains around 153 calories and 14 grams of alcohol.

During the average of 13 years of followup, the women tended to gain weight. A total of 7,942 (41.3 per cent) of the women who initially had a normal weight became overweight with a BMI of 25 or higher, including 732 women (3.8 per cent) who became obese with a BMI or 30 or higher.

Women younger than 50 who drank low to moderate amounts of alcohol, between 15 grams to less than 30 grams per day, had 0.68 times the risk of becoming overweight or obese compared with women of the same age who were teetotallers, the researchers found.

Moderation key

The study's authors cautioned the findings should not be taken as a licence to drink.

"Taking into account the potential medical and psychosocial problems related to drinking alcohol, any recommendation on alcohol use should be made for the individual after carefully evaluating both adverse and beneficial effects of the drinking behaviour in a broad context," the researchers wrote.

Heavier drinkers also showed a higher likelihood of smoking and eating a less healthy diet, the study's authors noted, although the link between alcohol and low weight gain remained after taking these lifestyle factors into account. The relationship did not hold for older age groups.

It is also possible that women who drink compensate for the extra calories, given that the survey suggested women who drank also reported eating fewer calories.

"Male drinkers tend to add alcohol to their daily dietary intake, whereas female drinkers usually substitute alcohol for other foods without increasing total energy intake," the study's authors said.

The researchers suggested that women's bodies may metabolize alcohol differently than men, which could affect weight gain. They called for more studies to investigate the role of alcohol intake and metabolism and to identify how behavioural, physiological and genetic factors may influence the effects of alcohol.

The findings lend evidence for the importance of moderation.

"If these women have a healthy diet and lifestyle and are having one or two units of alcohol a night, then that has fewer calories than someone who instead has a chocolate bar to unwind," Catherine Collins, a spokeswoman for the British Dietetic Association, told the Telegraph. "It's a question of 'What's your poison?'"

In February 2009, British researchers concluded that low to moderate alcohol consumption may account for nearly 13 per cent of the cancers studied in Britain, including breast cancer, and cancer of the pharynx.

A commentary accompanying the earlier study in the Journal of the National Cancer Institute concluded that no level of alcohol consumption can be considered safe.

In the U.S., guidelines recommend that women consume no more than one drink a day and two a day for men.