WASHINGTON — Ice cream lovers beware: The government knows you’re unlikely to stop after half a cup. New nutrition labels proposed Thursday for many popular foods, including ice cream, aim to more accurately reflect what people actually eat. And the proposal would make calorie counts on labels more prominent, too, reflecting that nutritionists now focus more on calories than fat. For the first time, labels also would be required to list any sugars that are added by manufacturers. In one example of the change, the estimated serving size for ice cream would jump from a half cup to a cup, so the calorie listing on the label would double as well. The idea behind the change, the first overhaul of the labels in two decades, isn’t that the government thinks people should be eating twice as much; it’s that they should understand how many calories are in what they already are eating.