Calories are the most-looked-at number on the Nutrition Facts label, which is why the 2016 redesign made them large and bold. But what is a calorie, and how much should the number worry you?
What a calorie is
A calorie is a unit of energy — specifically, the food 'calorie' (kilocalorie) is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. Your body uses that energy to move, think, breathe, and stay warm. Eat more energy than you burn and the surplus is stored, mostly as fat; eat less and your body draws on reserves.
Where calories come from
Calories come from the three macronutrients, plus alcohol:
- Carbohydrate: about 4 calories per gram
- Protein: about 4 calories per gram
- Fat: about 9 calories per gram
- Alcohol: about 7 calories per gram
These are the Atwater factors, named for the 19th-century scientist who measured them. They're why fatty foods are calorie-dense: fat packs more than twice the energy of carbs or protein per gram. It's also how you can estimate calories from a label's macros.
Liquid calories are different
Calories from drinks are uniquely easy to over-consume because liquids don't trigger fullness the way solid food does. A 500-calorie meal fills you up; a 500-calorie blended coffee doesn't, and you're likely to eat a full meal on top of it. This is a major reason sugar-sweetened beverages are linked to weight gain.
Why calories aren't everything
Two foods with identical calories can be nutritionally worlds apart — 200 calories of almonds versus 200 calories of soda deliver very different fiber, protein, and added sugar. Use calories alongside the % Daily Value for added sugars, sodium, and fiber to judge overall quality.