In this large cohort of middle-aged and older women, we found that compared to consuming no alcohol at all, light-to-moderate alcohol consumption was associated with smaller weight gain and a lower risk of becoming overweight and/or obese during 13 years of follow-up. These associations remained highly significant after adjustment for multiple lifestyle, clinical, and dietary factors. To our knowledge, this is the first study that has examined the association between alcohol consumption and risk of developing clinically defined overweight and obesity among initially normal-weight individuals.
Previous cross-sectional studies of alcohol intake and body weight have shown positive6–9
associations in men and inverse7, 10–13, 15
or null6, 16
associations in women. Prospective studies that focused on weight change have been equally inconsistent across populations. In the Framingham Heart Study, both men and women who increased their alcohol consumption during 20 years of follow-up experienced weight gains larger than the average.31
In the Nurses Health Study (NHS) I, an inverse association between alcohol intake and 8-year weight gain was found among 31,940 non-smoking women.32
A similar association was noted in the NHS II: light-to-moderate alcohol intake up to 30 g/day, but not exceeding 30 g/day, was inversely associated with weight gain and the odds of weight gain ≥5 kg in 8 years.20
In the NHANES I Epidemiologic Follow-up Study of 7,230 participants, women (p, trend = 0.006) but not men (p, trend = 0.11) who consumed alcohol gained less weight over 10 years than those who did not.19
Among Chinese adults, alcohol consumption was associated with a significantly greater risk of >5 kg weight gain over 8 years in men (RR=1.55) but not in women (RR=1.08);33
for both Finnish men and women, drinking alcohol >75 g/week was associated with a significantly higher risk of ≥5 kg weight gain over 5.7 years;16
and for British men, alcohol consumption of ≥30 g/day significantly increased BMI and the risk of weight gain ≥4% over a 5-year period (OR=1.29) compared to none/occasional drinkers.17
In contrast to these studies, two cohort studies found no significant association between alcohol intake and weight change in either men or women.18, 34
None of these studies investigated the development of clinically defined overweight or obesity as the endpoint.
The association of alcohol consumption with body weight change and development of obesity seems to differ by gender, which must be considered in the context of energy balance. Male drinkers tend to add alcohol to their daily dietary intake, while female drinkers usually substitute alcohol for other foods without increasing total energy intake.11, 35
Consistent with previous findings,7, 10, 11, 14
our study showed that women consuming more alcohol had lower energy intake from non-alcohol source, particularly carbohydrates. On the other hand, there may also be gender-specific differences in the metabolism of alcohol. Compared with male drinkers, female drinkers appear to have a lower activity of alcohol dehydrogenase36
and thus are more likely to degrade ethanol through other pathways such as the hepatic microsomal ethanol oxidizing system, which has a low efficiency of energy utilization and a high energy expenditure.37
Metabolic studies have shown that after drinking alcohol, energy expenditure moderately changed in men38
but substantially increased beyond the energy content of consumed alcohol in women.39
Taken together, regular alcohol consumption would potentially result in a gain of energy balance in men while a net energy loss in women. There have been other mechanisms through which alcohol may modify energy balance and subsequently body weight, including impact on nutrient digestion and absorption, interference with lipid oxidation and fat accumulation,5
increased sympathetic tone and associated thermogenesis, and enhanced adenosine triphosphate (ATP) breakdown.40
Complex interrelationships of alcohol consumption with various lifestyle, clinical, and physiological factors involve in the effect of alcohol drinking on body weight change, and thus partially explain the inconsistent findings in epidemiologic studies. For example, drinking habits may change appetite and the perception of satiety, whereby alcohol drinkers would prefer certain diet.7, 9–11, 15
Alcohol metabolism appears more efficient in heavy subjects,38
therefore alcohol intake may be more likely to promote weight gain in overweight women than in lean women.41, 42
In our study, higher alcohol consumption was generally associated with more current smoking, more physical activity, slightly lower baseline BMI, and less healthy diet. However, the association between light-to-moderate alcohol intake and smaller weight gain and lower risk of becoming overweight or obese remained strong after multivariate adjustment and in subgroup analyses, indicating that alcohol consumption may independently affect body weight beyond its impact through dietary and lifestyle factors. Since body weight change and body mass composition vary by age, we also specifically stratified our analyses by baseline age. As expected, we found that weight gain gradually diminished with increasing age. Nevertheless, the trend of association between alcohol intake and body weight change were similar across different age groups.
In this study, we cannot separate former drinkers who stopped drinking due to illness from lifelong abstainers. However, this should not substantially influence our study results, because the WHS cohort had excluded participants with major chronic diseases at baseline. We also excluded women with baseline diabetes from our analyses. In the sensitivity analyses, we further censored women who developed major illness during follow-up and the results remained unchanged. Our study results only apply to light-to-moderate alcohol consumption in association with body weight change. Because very few women in our study reported heavy alcohol intake, we cannot reasonably evaluate the role of heavy alcohol drinking in body weight gain and development of obesity. In our baseline population of women with normal BMI, only 3% consumed alcohol ≥30g/day (corresponding to ≥2–3 drinks per day). In this highest alcohol consumption category, as many as one third of women were current smokers, suggesting that heavy drinkers may have remarkably different lifestyle patterns compared with those consuming lower amounts of alcohol.
Several limitations of this study deserve comment. First, although previous studies have demonstrated excellent validity of self-reported body weight in health professionals,27
self-reported weight remains subject to random misclassification, which would tend to bias our results towards the null and underestimate the true effect. Similarly underreport or underestimation of alcohol intake is possible, and a single baseline assessment did not account for changes over time. However, sensitivity analyses that modeled alcohol intake as a time-dependent variable with update at 48-and 108-month follow-up have obtained similar results. Second, because the questionnaire used in the WHS did not collect detailed information on drinking pattern, we could not differentiate women who had a small drink in most days of the week from those who consumed multiple drinks in one day per week. Third, as in all observational studies, residual confounding cannot be completely ruled out. However, the observed associations in our study were robust after adjusting for a variety of dietary, lifestyle, and clinical factors, suggesting that the associations are unlikely to be explained by strong confounding. Finally, WHS participants were predominantly white female health professionals, which minimized potential confounding by race/ethnicity and socioeconomic factors but also limited the generalizability of our study results to other populations.
In conclusion, we found that during a long-term follow-up of middle-aged and older, initially normal-weight women, light-to-moderate alcohol consumption was associated with smaller weight gain and a lower risk of becoming overweight and/or obese compared to abstention. These associations persisted after multivariate adjustment and in subgroup analyses. Our study results suggest that women who have normal body weight and consume light-to-moderate alcohol could maintain their drinking habits without gaining excessive weight. However, taking into account the potential medical and psychosocial problems related to alcohol drinking, any recommendation on alcohol use should be made for the individual after carefully evaluating both adverse and beneficial effects of the drinking behavior in a broad context. Further investigations are warranted to elucidate the role of alcohol intake and alcohol metabolism in energy balance, and identify behavioral, physiological, and genetic factors that may modify the alcohol effects.