The following is a public service announcement on a topic most people would probably rather not think about. Truth be told, I'd rather not think about it. But you just might be glad to know about this someday anyway, so I'm going to tell you what I've learned recently.
Here's a scenario for you: It's Friday. You meet a couple of your close friends and a dozen of your favorite acquaintances for a nice meal. Over the course of several hours, you have a couple of beers. You get a mild buzz but don't drink nearly enough to give you a hangover the next morning, and you're happy. People are good. Life is good. You have an absolutely fabulous Friday evening, and think that you've just started the weekend in one of the best possible ways.
You then go home, go to bed, and have an absolutely miserable Friday night.
Saturday morning you get up and type a question into your favorite search engine: Can alcohol cause diarrhea? In .11 seconds you get over two and a half million results, all of which inform you that the answer is a decided YES.
Turns out that alcohol impairs the body's ability to absorb water. As cells in the intestines absorb the alcohol you've consumed, its toxicity disrupts the cells' ability to absorb water. Your intestines are flooded with liquid, which has to go somewhere.
Second, carbonation, which is present in sparkling wine (including champagne) as well as most modern beers, ales and ciders, can irritate your GI tract. Carbonated water is more acidic, which can be good if you want to kill bacteria in liquid, but bad if your intestines are already upset. Also, more bubbles and gas aren't really a good thing to add to the mix if things aren't working the way they should be.
Also, with beer, there's the possibility of gluten intolerance. (That's right: if you can't have gluten, you can't have beer.) I don't think that's my problem because I don't generally have trouble with gluten, but others might want to know.
If you're 24 and rarely drink, you probably won't have any problem from a couple of beers. If you're 40-something with a history of GI problems, you might want to limit yourself to one vodka tonic. You might not feel quite so rosy throughout the evening, but you'll have a much better weekend over all.
To your health.