Calories 101- What Is A Calorie?

What do you think of when you hear the word “calorie”? Do you imagine this evil, invisible, army that makes you gain weight at night? You don’t have to think of calories as a negative part of your day. Calories are actually essential for life and, in the correct amount, provide the fuel that you need to get through your day. Understanding what calories are is the first step to controlling this important factor in weight loss.

What are Calories?

Calories are the energy in food that fuels your body. They are essential. Your body needs energy to survive and perform functions, such as breathing, pumping blood, and moving muscles. This energy comes from the calories that you consume every day. Throughout the day, the body burns calories through the metabolic processes where enzymes break down food for digestion, through voluntary and involuntary movements and functions in the body, and through exercise.

Calories are a unit of measurement. The term “calorie” is used to describe two different words: calorie (lowercase c) and Calorie (uppercase C), also known as Kilocalorie. A calorie (lowercase C) is the amount of heat required to raise the temperature of one gram of water one degree Celsius. Calorie (uppercase C), or Kilocalorie, is a unit of measurement equal to 1000 calories. The calories that you see on the nutrition label for food are actually Kilocalories and not calories. The fitness and nutrition community uses these terms interchangeably though, with calorie being the most commonly used term to cover both. This article will use the term calorie.

I Burn Calories Just Existing as a Human Being?

Yes. Your body needs a certain amount of energy everyday to function at rest. This number is called your basal metabolic rate, or BMR. The number one factor that determines your BMR is lean body mass, or how much muscle you have. The more muscle that you have, the more energy your body needs to maintain itself. The basal metabolic rate accounts for approximately 50- 60% of calories that you burn in a day.

The Laws of Thermodynamics

Thermodynamics is the study of energy. There are three laws of thermodynamics that look at the transfer of heat as energy, the first of which, directly applies to fitness and weight management.  The first law of thermodynamics states that energy cannot be created or destroyed in an isolated system. In the body, energy (calories) cannot be created or destroyed, meaning that the body will not just produce calories or burn calories without effort to do so. Calories must be consumed through food or drink, and calories must be burned through daily living and exercise.

Thermic Effect of Food

The thermic effect of food, or TEF, is the amount of energy expended as a result of the processing of food for storage and use. As you consume food, your body requires a certain amount of energy for digestion, which increases your metabolic rate for a short amount of time following a meal. This is commonly referred to as the afterburn. There is a slightly higher afterburn in meals that are higher in protein. This isn’t a magical solution for weight loss though because the total thermic effect of food is only approximately 6-10% of the calories that were consumed in that one meal. For example, if you eat a 300 calorie meal, only around 30 calories will be used for digestion.

So if I Eat More Often, I’ll Burn More Calories?

No. The thermic effect of food is based on quantity of food consumed, not frequency. Your eating schedule should reflect your lifestyle and what works best for you to control hunger and provide your body with adequate nutrients.

Now you know, calories are a unit of measurement for the energy in food and drinks that fuel the body. The body needs calories for every function and any movement that you do. They are an essential part of life and a tool that you can use as you pursue your goal.



Related Links


  1. Boundless. “The Three Laws of Thermodynamics.” Boundless Chemistry. Boundless, 02 Jun. 2016. Retrieved 13 Jul. 2016 from
  2. 2012. NASM Essentials of Personal Fitness Training. Fourth Edition. Philadelphia, PA. Lippincott Williams & WIlkins, a Wolters Kluwer business.



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