How much did that afternoon snack cut into your daily allowance of calories?

The U.S. government wants food companies to make the answer clear on product labels.

A U.S. Food and Drug Administration proposal, expected to be released next month, would tell food manufacturers for the first time to list on packages the percentage of daily recommended calories the product contains, Acting FDA Commissioner Lester Crawford said on Friday.

The purpose is to “shock you and tell you (that) you have consumed 50 percent of your daily calories,” Crawford said at a meeting of the FDA Science Board.

The percentage will be based on a daily diet of 2,000 calories.

“So that milkshake may have been great, but it may have been costly,” Crawford said.

The FDA wants food labels revamped in order to help consumers get more useful information about fat, calorie and carbohydrate content, and to encourage healthy choices to help fight the U.S. Obesity epidemic.

Nearly two-thirds of the U.S. adult population is overweight or obese, according to the National Institutes of Health.

With many Americans trying “low-carb” diets to lose weight, the FDA will specify how manufacturers should describe carbohydrate content on their packaging.

The rules will aim to “demystify” carbs for consumers, as well as set forth standards that FDA can enforce, Crawford said.

“This will give our regulatory people the means to control this,” he said.

Obesity is defined as having a body mass index or BMI - a weight-for-height ratio - of more than 30. For an average woman, that usually means being 30 pounds overweight and, for an average man, 35 to 40 pounds.

The FDA will take public comments on the proposals before making them final, Crawford said.