Calorie Definition and Why We Count Them

A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. Calories in food provide energy in the form of heat so that our bodies can function. Our bodies store and "burn" calories as fuel. Many people who are trying to reach or maintain a healthy weight will count calories and try to decrease caloric intake.

What Is a Calorie?

You may think that calories are only important to people trying to lose weight. We often hear that people eat fewer calories or burn more calories with exercise to lose weight. But calories are important for everyone.

A calorie isn't actually a thing, it's a unit of measurement. A calorie measures the amount of energy in the food and beverages that we consume. We all need this energy to live and stay healthy. Everything we do relies on the energy that comes in the form of calories.

The food we eat becomes the fuel that runs our bodies. Healthy food provides calories (energy) and important nutrients to build strong bones and muscles. Drinks also contain calories. But not all calories are healthy. Sodas, for example, are often referred to as "empty calories." That means that they provide calories but have no other nutritional value.

Calorie vs. Kilocalorie

When the word "calorie" is used in nutrition settings or by consumers who are talking about food, they are usually using a casual definition of calorie. But they are actually referring to kilocalories, which is what you see on nutrition labels. This is how the two terms are different:

  • The definition of calorie (cal), or small calorie, is the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius.
  • The definition of kilocalories (kcal), or large calorie, is the amount of heat needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. A kilocalorie is equivalent to 1000 small calories. Kilocalories are sometimes called "food calories" or simply shortened to "calories" when referring to the energy in food.

Another unit of measurement used to quantify energy is called the "joule." One small calorie is equivalent to just under 4.2 joules. One kilocalorie (kcal) is equivalent to approximately 4.2 kilojoules.

Calories and Weight Gain

Calories in food provide essential energy, but if you consume too many you will gain weight. Excess calories are stored as body fat. Your body needs some stored fat to stay healthy. But too much fat can cause health problems.

So how do you make sure that you don't eat too many calories? It's important that you understand your caloric needs. That is the number of calories your body needs to perform basic metabolic functions and daily physical activities. You can calculate your caloric needs using an online calculator.

The daily recommended caloric intake for the average American can range from 1,600 to 3,000 calories per day. But that number is a general estimate and there are many variables for individual needs. Men can eat a little more, women should eat less because their bodies are smaller and need less fuel. Your individual calorie needs depend on several factors such as your activity level and metabolism.

Calories in Food

Different types of food provide different levels of energy. That is, the three macronutrients are not all equal in the number of calories they provide. Protein and carbohydrate have less than half of the calories per gram as fat does.

Macronutrient Calories per Gram:

  • Carbohydrate: 4 calories per gram
  • Fat: 9 calories per gram
  • Protein: 4 calories per gram

Because fat provides more calories per gram, many healthy eaters try to limit the amount of fat in their diet. But some types of fat are necessary for a healthy body. Polyunsaturated fat, for example, helps you to maintain a healthy heart. And even though carbohydrates provide fewer calories, some carbs are not as healthy as others. Refined carbohydrates, for example, are considered empty calories.

So are all calories the same when it comes to weight loss? Experts generally agree that a calorie is a calorie. It doesn't necessarily matter where your calories come from. To lose weight, you need to consume less and burn more.

However, some calories provide weight loss benefits. For example, calories from protein are helpful in building and maintaining muscle. When you have more muscle, you are better able to stay active during the day and burn more calories. And calories from foods rich in fiber help you to feel full and satisfied throughout the day so you eat less and slim down.

How to Count Calories

Experts estimate that if you consume approximately 3,500 excess calories you will gain one pound, though this has been dispute. The theory states that to lose one pound, you need to create a calorie deficit. You need to decrease your caloric intake by 3500 calories or burn an extra 3500 calories. You can also combine both methods to reach the correct calorie deficit.

You can reduce your caloric intake by 500 calories per day to lose 1 pound each week. A 1–2 pound decrease in weight per week is considered a healthy and sustainable rate of weight loss.

The most important thing to remember is to not cut calories too drastically. Going on a very low-calorie fad diet can put your health at risk and cause health problems.

A Word From Verywell

There are many different ways to lose weight and to maintain a healthy diet. Counting calories is just one of them. Portion control and choosing nutrient-rich foods are important factors, too. But we believe that calories are important. If you want to learn more about your own calorie needs, check out our recipes and use the recipe nutrition calculator to see how many calories are in your favorite foods.

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Article Sources
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  1. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015–2020 Dietary Guidelines for Americans. 8th Edition. December 2015.

  2. Hall KD, Chow CC. Why is the 3500 kcal per pound weight loss rule wrong?. Int J Obes (Lond). 2013;37(12):1614. doi:10.1038%2Fijo.2013.112