I wonder how that would affect the calories of the alcohol. Apparently the ethanol gets broken down into acetic acid, which I believe can't be digested further? Does that mean you also wouldn't gain weight when drinking dry beer or wine?
EDIT: Apparently acetic acid _does_ have calories. Didn't know that.
> Apparently acetic acid _does_ have calories. Didn't know that.
Calories are measured by burning the substance. While it very precisely determines contained energy in the physics sense, it's a question whether all that energy is used by digestion? Especially if it's something the body treats as a toxin and wants to remove as soon as possible?
A bit pedantic but burning is a chemical reaction, and redox reactions are redox reactions no matter where they're happening.
Also, substances like ethanol and acetic acid are not digested, they pretty much just go straight into the bloodstream. There is a limit on how much e.g. ethanol the liver can process per hour, which does put a cap on how many of ethanol's calories are released as ATP + body heat. Acetic acid is a normal temporary metabolite though and so its consumption is much more complete (it gets used by cells all over).
From this article[0] it seems ~60% of the calories in lager come from the alcohol - presumably ~40% come from carbohydrates. And from Google, acetic acid is 349 kcal / 100g, versus pure ethanol at 700 kcal / 100g. So if this approach converted 100% of alcohol to acetic acid, you'd drop the calories from lager by ~30% overall. To your question, dry wine or lower-carb beer would be proportionally even better.
The flip-side of this is perhaps consumption of too much acetic acid! It's impossible to calculate potential toxicity without understanding the strength of the acetic acid generated, though.
> And from Google, acetic acid is 349 kcal / 100g, versus pure ethanol at 700 kcal / 100g.
Metabolism matters. Gasoline is over 800kcal/100g, but you wouldn't get that much from it (if anything at all).
Alcohol has a particularly long metabolic pathway, which after ingesting approximately 20-30g gets cut short to one where acetic acid is excreted (commonly known as "breaking the seal") and the overall upper energy yield limit becomes approximately 110kcal/100g.
Executive summary is that on a given session it's the first two 12oz (330ml) beers which provide most of the calories from alcohol and their contribution is on par with a snickers bar.
EDIT: Apparently acetic acid _does_ have calories. Didn't know that.