Our bodies are constantly burning calories (energy) throughout the day, even when we are resting. The calories burned come from two primary sources- sugar (broken down from any carbohydrates we’ve eaten) and fats (mostly from the oxidation of stored body fat). The percentages burned of each vary, depending on the level of activity being performed at the moment and the amount of “fuel” (food) available to burn.
Enter alcohol- when we ingest alcohol these numbers go out the window. The byproduct of alcohol digestion (acetate) becomes the body’s new favorite energy source. It can’t be stored by the body and our bodies are not wasteful! We’ll burn all the acetate available BEFORE burning any more sugar or fat. This means that during the time that blood alcohol levels are elevated, very little fat or sugar is being used at all. This becomes a two-edged sword- the bodyfat we’re trying to burn by exercising remains unscathed while the sugars available to the body ARE stored, very easily, as bodyfat.
In addition to this, alcohol contributes to diminished inhibitions, so we don’t pay as much attention to what we’re eating in addition to the booze. (mmmm, nachos!) In the hours after alcohol is metabolized, blood sugar levels tend to drop because of a deficiency in one of the acids necessary to complete the Krebs Cycle. This means we get HUNGRY (aka hungover) and crave foods with higher carb content than we really need. Guess where the excess is stored?? That’s right, as bodyfat.
As for where the fat is stored, most of it depends on genetics and gender. However, there’s an interesting study from 2007 published in the Journal of Clinical Endocrinology & Metabolism correlating alcohol consumption and the release of cortisol, a hormone specifically linked to visceral (belly) fat storage patterns. It shows cortisol levels increasing 3% for every one alcoholic beverage consumed per week. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2266962/
Basically, as you know, moderation is key when it comes to alcohol consumption. Sorry for the lengthy description, but I hope it helps. If you want further resources for your clients, www.livestrong.com has some great articles, as does www.webmd.com .