What Is A Calorie? Defining Calories And Why They’re So Important

What is a calorie? While most people understand the concept of calories consumed vs calories burned as it pertains to weight loss, not everyone fully understands exactly what is a calorie.

Most people have an idea of what calories are, but perhaps not in scientific terms. You may have seen a fitness app telling you how many calories you can burn if you run or cycle for an hour. You may have noticed calories listed in the form of numbers on nutritional labels of food.

In today’s world, calories are often villainized if consumed in excess. Calories are often seen as the source of all weight gain, and are therefore connected with self-esteem issues, disordered eating behaviours, food guilt, and eating disorders. However, in the bigger picture, calories aren’t the enemy. Calories are units of energy essential to our survival.

We need calories to power our brain, metabolism, muscles, and our organs. Without them, we simply couldn’t live. However, it’s worth noting there are different types of calories, and various methods in which we can track, use, and reduce calories in order to achieve our health goals.

Let’s officially answer the question: What is a calorie?

What is a Calorie and How is it Measured?

As mentioned, a calorie is a unit of energy.

Everything we consume, whether it’s a can of soda, a fresh salad, or a bag of M&Ms, has its own unique number of calories. Essentially, the higher the energy provided by the substance, the greater the number of calories. However, our bodies only need a certain number of calories each day to function.

When we consume excess calories (more calories than we actually need to function and perform our daily tasks) the additional energy is stored in our body for later use. It’s often stored as fat. This is how we gain weight. The key to preserving a healthy weight is knowing how to get the right number of calories, from the right sources.

The term ‘calorie’ was first introduced in 1845, in the Bescherelle 1845 Dictionnaire National. Here, it was defined as the amount of heat required to raise the temperature of a kilogram of water by a single degree. By 1894, scientists began using calories and kilocalories (kcal) to measure human energy needs. Today, you can still see calories measured in kcal on nutrition labels.

Virtually all countries around the world require food manufacturers to include kcal measurements on their food labels. In fact, during the 1990s, the US government passed the Nutritional Labelling and Education Act, which standardizes the information any nutritional label must disclose.

Calories are so important that that information has to be disclosed on the foods we buy, especially since eating excess calories can be so bad for you.

This means any company that produces food, first needs to calculate the total quantity of calories in the item (this applies to beverages too). One way to measure calories is through a tool called a bomb calorimeter. To measure calories with a bomb calorimeter, scientists place the substance in question in a sealed container surrounded by water, then heat it until the food is completely burned away. Scientists then record the rise in water temperature to determine the number of calories in the product.

The 4-9-4 Rule of Calories

Another way of measuring calories is with a method introduced by a US Chemist named Wilbur Atwater, called the 4-9-4 system. Most US manufacturers still use this methodology, introduced in the 1800s, while other countries have begun to invest in more advanced tools for measuring calories.

The 4-9-4 method is considered by some experts to be more effective than using a calorimeter. The standard calorimeter doesn’t account for the fact that humans lose calories through heat, as well as through the passing of waste (feces and urine). Atwater addressed this limitation by calculating the number of calories in different foods, then testing feces to see how many calories were expelled.

The experiments revealed that proteins and carbohydrates each have around 4 calories per gram, while fats have around 9 calories per gram. This is why fattier foods tend to be higher in calories than foods rich in proteins and carbohydrates. Wilbur also found alcohol has around 7 calories per gram.

How Many Calories Do Humans Need?

If you’re asking what is a calorie? you may also be wondering how many you need on a day-to-day basis to survive. Over the years, numerous scientists have attempted to answer this question. The Dietary Guidelines for Americans available today suggest women should consume between 1,600 and 2,000 calories per day, while men should consume between 2,000 and 3,000 calories per day.

However, these are just basic guidelines, meant to apply to most people. The exact number of calories you need to maintain good health can depend on numerous factors, including your height, weight, age, gender, medical status, weight loss recommendations from your doctor, and even how much muscle mass you have.

Some people who are trying to lose weight might eat 1,400 or 1,500 calories per day if it’s advised by their healthcare provider.

The temperature of the environment around you can decrease or increase your calorie needs, by altering the way your body processes energy. Similarly, your internal hormone levels can also dictate how energy is used and processed by the body. This is one of the reasons why pregnant women tend to need more calories than their counterparts.

Once they have their baby, if they’re breastfeeding, they’ll also need to eat extra calories during that time that they’re on a breastfeeding diet.

Exercise and level of physical activity also affects how many calories we need to consume, since we burn calories exercising. Calories, as a unit of energy, are consumed by the body in everything we do. Even sitting and breathing consumes calories. The more you use your muscles and expend your energy, the more calories you’ll need to consume.

Are there Different Types of Calories?

One of the reasons so many people struggle with the question: what is a calorie? is that this unit of energy can come in many different forms. While all calories measure the same thing, some foods provide more nutritional value than others. This is why some calories are referred to as being ‘empty calories’, while other foods are described as being ‘nutrient dense’.

Some of the core types of calories you may need to be aware of include:

Macronutrient Calories

Broadly, there are three types of macronutrients which feature calories: carbohydrates, protein, and fats. As mentioned above, each of these macronutrients offer a different number of calories per gram. While both carbohydrates and protein consist of 4 calories per gram, fat contains 9 calories per gram.

Some people assume they should remove fats from their diet because of its high calorie level. However, healthy fats are actually crucial to our wellbeing. Polyunsaturated fats, for instance, are valuable for heart health. Even the US Department of Health recommends getting 20-35% of our daily calories from fat. Alternatively, 10-35% of your daily calorie intake should come from protein, and 45-65% should come from carbohydrates.

Empty Calories

An empty calorie is one that offers access to energy, but no additional nutritional value. For instance, if you eat a chocolate bar filled with fats and sugar, a lot of the calories in the bar will be nutritionally empty. While you may still get an energy boost from the calories, you won’t be supporting your body with any valuable components such as protein, minerals, or fibre.

Consuming too many empty calories can cause a range of problems, from blood sugar spikes, to increased inflammation. They can also contribute to chronic health issues such as heart disease and diabetes. In some cases, eating too many empty calories can also cause weight gain. Even if you get all of your daily recommended calories from empty calories, you may eat more in order to fulfil your other nutritional needs. This leaves you with more excess energy to store as glucose and fat.

Nutrient Dense Foods

Foods described as nutrient dense are often high in valuable vitamins, minerals, and compounds, but low in calories. Vegetables, fruits, whole grains, and seafood all contain significant levels of nutrients, but they’re not particularly high in carbs, or fats, which means their calorie content is also low.

Typically, if you’re trying to lose weight, it’s best to focus on filling your diet with nutrient-dense foods. Eating too many foods low in nutrients can also cause a number of issues, including accelerated aging, low energy, fatigue, stress, depression, and brain fog.

Low or Zero-Calorie Foods

Some foods and beverages claim to have low calories, or none at all. You’ve probably noticed diet sodas and similar drinks boasting a 0 calorie promise. What this really means is these foods contain none of the fats, proteins, or carbohydrates required to create calories.

However, no-calorie foods can be both healthy, and unhealthy. Water is one of the healthiest no-calorie substances there is. Unfortunately, it also contains no other sources of nutrition, which means we can’t survive on water alone. Remember, we need calories to thrive.

In some cases, no-calorie foods can also include additional ingredients, to help replicate the flavor missing due to the lost calories. For instance, artificial sweeteners are common in diet sodas. These substances are often associated with weight gain and increased food cravings.

How Do Calories Influence Your Weight?

What is a calorie in the context of body weight?

Calories can be a useful tool for controlling your weight. If you’re trying to lose weight, then a calorie deficit can be helpful. The fewer calories you eat, the more your body will need to tap into its energy stores, such as fat and glucose, to remain active. This means you end up burning the extra energy you’ve stored by eating more calories than your body needs.

However, a calorie deficit is unlikely to cause significant, sustainable weight loss on its own. You’ll still need to commit to regular exercise to burn calories. You’ll also need to ensure you’re getting the right nutrition from the calories you do it, to keep your body fit and healthy.

In some cases, calories can also help people to gain weight. Having an extremely low weight might seem desirable in today’s society, but it can also be problematic.

Our bodies need a certain amount of fat and muscle to operate normally. People with a low body mass can suffer from a lower immune system, and poor athletic performance. Women can even encounter fertility issues when they’re excessively underweight.

To gain weight, you’ll need a calorie surplus. However, once again, it’s important to ensure the excess calories you get are coming from the right sources. Empty calories won’t help the body to build muscle, generate energy, and protect the body with immune-boosting antioxidants. However, nutrient dense foods can deliver all of these benefits.

Understanding What Calories Are

The answer to the question, what is a calorie is simple. Calories are a unit of energy. They’re something we need to feed our muscles, stay fit, feed our brain and be healthy. However, we can more carefully choose the calories we consume, and how they influence our bodies.

Choosing nutrient-dense, beneficial calories, instead of their empty alternatives, can help to keep us fit and strong, and help us maintain a healthy weight. Counting calories safely can also help us to achieve our weight loss goals, and be more mindful about what we eat.

Did you know that a CircleDNA test can give you an insight into your daily calorie requirements, your genetic risk of obesity, and your nutrient needs based on your genetic makeup? Swab your cheek with the CircleDNA kit from the comfort of your home, and find out the optimal diet plan for you based on your DNA, as well as tons of insight into your personality, behavior traits, ancestry, and more.


  1. NCBI: History of the calorie in nutrition https://pubmed.ncbi.nlm.nih.gov/17116702/#:~:text=The Calorie was already defined,0 to 1 degrees C
  2. Science Direct: Bomb Calorimeter
  3. ESHA: How Calories are Calculated in Different Countries
    https://esha.com/blog/calorie-calculation-country/#:~:text=In the U.S.%2C most manufacturers,Atwater.
  4. Dietary Guidelines: Make Every Bite Count With the Dietary Guidelines
  5. Health.Gov: Dietary Reference Intakes (DRIs)

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