It has been long held that being in a calorie deficit is a common technique to utilize when trying to lose weight. (You've likely heard or seen the phrase "calories in < calories out" at some point, right?)

But what is a calorie deficit, anyway, and is cutting back on calories actually the best way to lose weight? Here's what nutrition experts and recent research say about calorie deficits, how to calculate a calorie deficit, and whether or not they're a good idea.

What Is a Calorie?

In terms of the human body, a calorie is a measurement that denotes the amount of food with a specific energy-producing value. Essentially, this all means that the food and beverages you consume provide your body with energy, measured in terms of calories, to live.

However, your body needs more than just calories to stay alive — you also need nutrients — including vitamins and minerals — in order to keep your body functioning well. (For example, the mineral calcium found in milk helps strengthen bones while the mineral iron found in beans is needed for red blood cell function.)