From a scientific perspective, a calorie is the amount of heat needed to raise the temperature of 1 kilogram of water by one degree Celsius. In nutrition, one calorie actually equals 1,000 of these scientific calories, which is why they're sometimes called kilocalories. How many calories you should eat every day depends on your weight, height, and activity level. The types of food those calories make up matter too: the ratio of carbohydrates, fat, and protein, not to mention added sugars, trans fats, and other unhealthy elements, can make a big difference in whether a food nourishes your body and satisfies your appetite or simply provides a short burst of energy that requires you to eat even more later.
Do you know what 200 calories looks like? Depending on the food, it could look drastically different. You can eat a four-ounce cut of salmon for 200 calories, or only about half a slice of pepperoni pizza. Not only is this a big size difference, it's also a huge difference in nutrition: 200 calories of salmon has nearly four times as much hunger-satisfying protein as that much pizza. Other comparisons might surprise you, though. When choosing between a bagel and a donut at breakfast, you might think the bagel is the lower-calorie choice. Not so: a Krispy Kreme glazed donut is only 190 calories, whereas you'd need to cut the portion of a sesame-seed bagel down to three-quarters to make the calories even out. Still, when it comes to nutrition, the bagel wins: it only has about 4 grams of sugar to the donut's 10 grams. Delve into the science of nutrition with the videos below.