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Mythbusters: Does alcohol make you fat?


may 2010 does alcohol make you fat

Daylight saving is over, and the shorter colder days make snuggling on the couch with takeaways and a bottle of wine much more tempting than getting outside to exercise. The winter padding is setting in, and rising obesity prevalence figures suggest this padding will be permanent for many. Is our national weight gain related to changes in alcohol consumption? What effect does alcohol really have on our waistlines?

Alcohol is a known appetite stimulant, and people tend to eat more when consuming alcohol. At 29kJ per gram, it’s also a high calorie beverage. One standard drink (100ml of wine, 30ml of spirits or 280ml of standard beer) contains 290kJ, about half the energy of a can of fizzy drink.

Theoretically, the potential for alcohol to increase weight is clear, but the evidence is surprisingly mixed. Some studies suggest calories from alcohol are more likely to cause weight gain in intermittent drinkers and in those already overweight than in heavy drinkers (the classic malnourished alcoholic). Others find alcohol is associated with weight loss in certain subjects.

This apparent contradiction is mostly because many of these studies are cross-sectional, looking at one point in time, and so cannot establish a temporal or causal link between alcohol consumption and weight. For example, an apparent association between higher body mass index (BMI) and ‘abstainers’ may be because overweight people have already stopped drinking for health reasons or to lose weight. More longitudinal studies are needed before firm conclusions can be made.

One recent and well publicised US longitudinal study found moderate alcohol consumption may help reduce weight gain in middle-aged to elderly women. However, before hitting the gin instead of the gym, it is worthwhile considering this study’s many limitations.

Firstly, only baseline alcohol consumption was used. The analyses did not take into account changing drinking habits over time. Secondly, participants self-reported their weight, which is notoriously unreliable. Thirdly, the selected subjects were predominantly white, female healthcare professionals who were not obese at baseline. This means the results cannot be extrapolated to men, less advantaged or non-white women, or women who are already obese.

Interestingly, a British study of middle-aged men that did account for changes in alcohol consumption over time showed higher BMIs in those with the heaviest alcohol consumption, which may point to the importance of collecting comprehensive data for these complex studies and perhaps a stronger association between alcohol and weight for men.

In addition to the identified limitations of the US study, the most important drawback with such observational studies is the many additional reasons people may drink (or abstain) and change weight that are unmeasured, such as personality, genetics, beliefs, health status and upbringing.

These confounding factors may make it appear alcohol is related to BMI, whereas the unmeasured factor is the real reason for the relationship. Unfortunately, observational studies are the best research tool for this question because ‘gold standard’ randomised experiments are not feasible – randomly allocating individuals to abstinence or heavy alcohol consumption to observe health effects is unlikely to be acceptable to either individuals or ethics committees!

But even if the results from the US study of women are true, what then? A single observational study cannot be used to recommend alcohol as a diet tonic to women because any potential weight-loss benefits must be considered against increased risk of cancer, liver disease, injury and other well known harms from alcohol.

Whatever the evidence linking alcohol and BMI ultimately shows, it is worth remembering that alcohol has three major characteristics: it is a nutrient (energy source), a psycho-active drug and a toxin. Alcohol is not solely a source of calories, but also a potentially addictive and lethal substance, and for many people, the effect of alcohol on their bodies may be far less significant than its effects on their lives.

References

Suter, P. 2004. Alcohol, nutrition and health maintenance: selected aspects. Proceedings of the Nutrition Society. 63(1):81-8

Suter, P. 2005. Is alcohol consumption a risk factor for weight gain and obesity? Critical Reviews in Clinical Laboratory Sciences 42(3):197-227

Wang, L. Lee, I-M. Manson, J. E. Buring, J. E. Sesso, H. D. 2010. Alcohol consumption, weight gain, and risk of becoming overweight in middle-aged and older women. Archives of Internal Medicine 170(5):453-61

Wannamethee, S. G. Shaper, A. G. 2003. Alcohol, body weight, and weight gain in middle-aged men. American Journal of Clinical Nutrition 77;1312-7

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