When I wrote about common science mythconceptions the other day, a reader on Twitter later asked whether it’s true that hardcore alcoholics would get most of their calories from the booze – a statement made on the poster I linked to.
According to Washington State University, alcohol yields 7 calories per gram – in comparison with the three macro-nutrient groups, only fat supplies more calories per gram (9 cal), while carbs and protein are averaged at 4 cal. Thus, a shot of vodka may contain almost 100 calories, while the same amount of orange juice would contain significantly less.
But is alcohol energy the same as food energy? Given how calorie content is measured, that’s unlikely:
The original method used to determine the number of kcals in a given food directly measured the energy it produced.The food was placed in a sealed container surrounded by water–an apparatus known as a bomb calorimeter. The food was completely burned and the resulting rise in water temperature was measured.
While this method is not commonly practised today, the above-mentioned average calorie content per gram for different food components is calculated based on the findings from this method. However, even though alcohol does burn well, the human body metabolises it somewhat differently. Unlike protein, which is digested by the body, releasing the calories as energy, there’s only so much alcohol we can actually use for this purpose before getting rather sick:
[..]the body wants to get rid of alcohol because it sees it as a toxin. One way to get rid of alcohol is to use it for energy. But, your liver can only process so much alcohol as energy before the body has to start dumping the excess as urine. Basically, from a physiological standpoint, if you have one drink slowly, you’ll probably digest most of the alcohol as energy. Drink heavily, and the calories don’t “count” as much, because you’ll end up excreting them.
Of course, we don’t always just drink alcohol in its pure form; drinks like beer and wine also contain sugars on top of the relatively benign alcohol calories, and once you get to a sweet or even cream-based cocktail, the calories in that can easily go through the roof.
In the end, it’s clear that a severe alcoholic could get quite a bit of digestible calories from their drink, even though it would mostly come in the form of carbs, particularly sugar. But that level of drinking would also make the person quite malnourished, because not only is alcohol toxic, but it also messes up the absorption of essential nutrients. I don’t think I would try to subsist on a beer diet.