Lydia DePillis's story last week about the imminent demise of low-cal liquor made me realize that I don't spend a lot of time thinking about the calorie content of booze. This isn't an accident — beer, wine and liquor manufacturers are held to very different labeling standards than other food and beverage makers, and those standards don't require the familiar "nutrition facts" you see everywhere else.

The history behind this is complicated and a little insane. After Prohibition, beer makers were actually forbidden from putting alcohol content information on their labels. They finally sued for the right to do so in 1987. Since then, ATF has been kicking around various labeling update proposals. Alcoholic beverage groups are generally on board with the idea, but they've been bickering among themselves over they types of information to be included on the labels. It's safe to say that nutrition facts for alcohol are quite a ways off.

So to figure out exactly how many calories you'll be packing away at your next happy hour, your first stop would be the National Nutrition Database for Standard Reference. Here, the USDA maintains a hilariously arbitrary selection of nutrition facts for a variety of alcoholic beverages. You'll find three types of coffee liqueur, three preparation methods for a whiskey sour and one mysterious entry for "tequila sunrise, canned." But within the realm of things that people actually drink, they do have useful entries for distilled liquors (rum, vodka, whiskey and gin), and averages for beer (regular and light) and wine (white and red).

I grabbed the calorie figures for these drinks and added a variety of others culled from elsewhere on the Web (there's a wide range of calories in beer, for instance, so I chose a handful of representatives). Among wines there isn't great caloric variety, but sparkling wines, port, and dessert wine are sufficiently distinct to warrant their own categories. For comparison purposes I added Coca-Cola, apple juice and 2 percent milk.

When it comes to calories per ounce, distilled liquors lead the pack: 100-proof rums, whiskeys, vodkas and gins contain more than 80 calories per ounce. This is nearly twice as much as fortified wines and three times as much as standard table wines. The distilled liquors are also roughly eight times as calorie-dense as Guinness beer. For a great explanation of why alcohol is so calorie-dense, check out this AskScience thread on Reddit from a few months ago. Another surprise is that the average ounce of plain ol' beer contains fewer calories than milk or apple juice — it's practically health food!

This chart also illustrates exactly why low-calorie wines haven't taken off. On a per-ounce basis, the Skinnygirl wine contains only five fewer calories than regular wine. If you're that calorie-conscious, you might as well simply drink sparkling wine, which contains even fewer calories.

But of course, nobody goes around drinking alcohol by the ounce. A serving of scotch is much smaller than a serving of beer, for instance, so the chart below breaks down calories per serving.

Here, the heavier beers and malt beverages dominate: A 12-ounce glass of Ommegang's Three Philosophers contains 288 calories, while a five-ounce serving of standard red or white wine contains less than half that.

But let's be honest. It's Friday night, you're heading out to the bars, and the likelihood of limiting yourself to just one drink is rapidly approaching zero. To get a calorie count for an average weekend night's consumption let's assume you'll have three drinks (according to the killjoys at the CDC, any more than that and you're a binge drinker). The damage is listed below.

As you can see, those three glasses of Ommegang just added 864 calories to your daily total — more than a big mac and fries. Three glasses of Skinnygirl wine contain exactly as many calories as one McDonald's cheeseburger. Calorie-wise the Bud Select 55 is the clear winner, but when you factor in alcohol content you are only a third as buzzed as the guy sitting next to you drinking Sierra Nevada IPA:

Finally, let's do the ultimate efficiency exercise: which beverage provides the greatest buzz on a per-calorie basis? As they say on the Internet, the results may surprise you:

Sparkling wine — with its low calorie count and relatively high alcohol content — is the clear buzz-per-calorie winner. Distilled liquors are not far behind. Here the Skinnygirl and Bud 55 make a respectable showing, but, again, if you're that concerned about calories, why not just drink champagne?