Quick nutrition science quiz. After carbs (4 kcal per gram), protein (4 kcal per gram), and fats (9 kcal per gram), what is the only other major source of human food energy? The answer is the alcohol in alcoholic beverages.
Yet, alcoholic beverages are exempt from federal nutrient labeling requirements. So, companies must tell you the amount of calories in lemonade, unless the lemonade is alcoholic, in which case you can be left in the dark.
This policy question is in the hands of the Alcohol and Tobacco Tax and Trade Bureau (TTB) of the Treasury Department, not the first name in federal sources of nutrition facts information. The TTB last year requested public comment (.pdf) on possible new nutrition labeling rules. Several consumer groups are in favor. On the one hand, with mandatory labeling, I would expect to start to see advertisements exaggerating the health benefits of moderate alcohol consumption. On the other hand, alcoholic beverages seem a strange class of products to exempt from disclosure rules.
TTB will announce its decision on next steps ... well, ... some day. In the meanwhile, the Consumer Federation of America last month released (.pdf) its own table (.pdf) of nutrition facts for leading products. There are some surprises. To continue the hard lemonade example, I would not have guessed that a serving of Mike's Hard Lemonade contained 220 kcal, about a tenth of a person's food energy needs for a day, mostly in the form of carbohydrates, not alcohol. But, now that I think about it, perhaps I should have guessed. I had one once. It tastes like high fructuse corn syrup.