Thursday, March 11, 2010

Will booze make you skinny?

Roll out the barrel because if you believe the news reports alcohol contains magical negative calories!

Yup a recent study is making waves in the media and blogosphere and the gist of the reporting is that a few alcoholic drinks a day may help control your weight - though of course that's not the whole story.

The study's a big one. It looked at 19,220 American women aged 38.9 years or older who had a baseline normal BMI and followed them for 12.9 years and tracked alcohol consumption and self reported exit weight.

As with any long term prospective study, the authors tried valiantly to control for potentially confounding variables and they adjusted for age, race, baseline BMI, smoking status, non-alcohol energy intake, physical activity, menopausal status, postmenopausal hormone use, multivitamin use, comorbid medical conditions, and macronutrient distribution. They then stratified results into alcohol intake by grams with a 5 level subdivision.

The results?

Firstly it's important to note that statistically all groups of women gained weight. Average weight gain for the women who didn't drink at all was 3.63kg over 12.9 years and for those drinking an average of 30g or more of alcohol daily the average weight gain was 1.55kg. That's a difference of 4.6lbs over nearly 13 years.

So best case scenario is the study has indeed accounted for all variables and the association is causal and if you're a woman, drinking 2 glasses of wine daily will help you not gain roughly a third of a pound extra per year.

Worse case scenario? The study proves just how difficult it is to study nutritional variables and that it's one of those association doesn't prove causality pieces.

The lead author, Dr. Lu Wang, very kindly responded to a few email questions regarding potential confounding variables and both in the paper and in her emails made it very clear the authors did a truly bang up job trying to control for everything they could think of. At the same time Dr. Wang readily admitted that there are,

"an endless list of potential confounders."
Given we're talking about a difference of only 4.6lbs over more than a decade of time, it would therefore certainly be possible there's some subtle difference or differences other than alcohol intake to account for the results.

But does that matter?

Ultimately research on heart disease and moderate drinking in women has already suggested benefit to tempered imbibing and with this study, perhaps there's more. More to the point of this post though, the press' reporting on this story has been abysmal with some articles suggesting that alcohol will cause weight loss, others not noting the small actual absolute differences seen in the study and sadly most of the articles doing a better job of reflecting the media's need to sensationalize study results than to practice good science journalism.

So will booze make you skinny? Nope. But maybe, just maybe it'll make you ever so slightly less fat.

Wang, L., Lee, I., Manson, J., Buring, J., & Sesso, H. (2010). Alcohol Consumption, Weight Gain, and Risk of Becoming Overweight in Middle-aged and Older Women Archives of Internal Medicine, 170 (5), 453-461 DOI: 10.1001/archinternmed.2009.527