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  • Writer's pictureRachel Turi, RD

A Calorie is a Unit of Energy. Don’t Forget It.

Updated: Oct 25, 2020



noun [ C ]

US /ˈkæl·ə·ri/

calorie noun [C] (FOOD)

a unit used in measuring the amount of energy food provides when eaten and digested.


Have you ever wondered what a calorie even is? Read the definition again. A calorie is literally a unit of energy. Most people don’t actually know what calories are, but rather what they are associated with. Somehow, sadly, the word has become synonymous with “bad,” or “weight gain” among others. Everyone is trying to cut down on calories, eat low calorie foods and products, and think less is more. But wait, I just said a calorie is a unit of energy...therefore, food is energy. If we eat food, we have energy to use. If we don’t eat food, we don’t have energy to use. So, if we are always trying to lower the amount of calories we consume we are, in reality, just reducing the amount of energy we put into our body to do everything it is supposed to do.

Okay, you get it. The body needs calories for energy. But what is that energy used for? To survive. To sustain life. Calories are necessary for all human functions- to breathe, to move, to pump blood throughout the body, to think. Every organ in the body uses energy to function. In fact, the brain itself uses about 600 calories (specifically from carbohydrate) to properly function per day. We even burn energy while we sleep! The amount of energy that each individual burns to sustain life varies based on gender, weight, height, age, muscle mass, and activity level. This is called a Basal Metabolic Rate. And that is just the start.

It also takes energy to break down food into its basic elements, which can then be used by the body. In other words, the body also uses caloric energy to digest the food we eat. This is called the Thermic Effect of Food. You may have heard the claim “celery has negative calories?” While the statement is ridiculous, and comes from a very diet centered world, it has a little bit of truth to it. The amount of calories we burn chewing and digesting celery could very well end up being more than the actual caloric energy that the celery itself provides. I tell you this not so that you go attempt to live off celery, but so that you better understand the concept.

Now you understand that you need food for energy and that energy is used to sustain life and all the body’s functions. But, there’s more! The body uses A LOT of energy to do exercise and physical activity. To run, bike, walk, stand, garden, cook, ski, kick a soccer ball, you name it- the body needs energy to do it. We all know we burn calories through exercise, but most people forget that it takes stored up energy to do that activity in the first place. If we aren’t eating enough calories to support this activity we will simply feel tired, sore, less motivated, and all of this results in lower quality of workout and few performance improvements. If you aren’t even eating enough energy to sustain life, then you certainly don’t have enough to train or perform to your full potential. You’ll get through it, but it means that other functions in the body are being sacrificed. In an effort to keep you alive and moving, the tissues and organs that make up your body will break down in a desperate attempt to make energy. Simply put, this is dangerous, especially long term.

Now, I’m not saying that eating too much never has negative consequences. If we eat too much and don’t listen to our hunger and fullness cues it can be harmful to our health as well. Eating more than we burn in a day can lead to weight gain, sure. But honestly, in the life of a highly active person, it is much safer to err on the side of more. You don’t want to sacrifice your body, nor do you want to perform poorly. And certainly nobody wants to be tired, injured, cranky, cold, or sick all the time- all of which will occur if we are constantly undereating.

All of this being said, I want you to take two things away from this article. First, stop demonizing food and calories. They are absolutely necessary for all parts of human survival and activity. Second, if you are undereating in an attempt to alter your body composition, no matter your relationship with food, please consult with a dietitian to decide a safe and effective plan of action.

Fuel up!

(Definition from:

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