top of page
  • Brian Bender, PhD

Calories in Food: Your Guide to Understanding Calories

Learning more about the calories in food is a great step towards improving your diet and nutritional health.

In this post, we’ll discuss in a detailed guide answers to questions like:

  • Where do the calories in food come from?

  • Which foods are calorie-dense?

  • How should you think about calories when thinking about your diet?

Where do the Calories in Food Come From?

The concept of nutritional calories comes from W.O. Atwater in 1887.

Although the concept of a calorie was already established for measuring heat energy from machines, Atwater introduced it as a similar unit for measure the energy available in the foods we eat.

This concept has survived to today, only changing its name to the joule (SI unit for energy) in more scientific circles.

Where is this energy stored within the calories in food?

Chemical bonds.

Think of the foods we eat as a molecular soup. If you were to look at your piece of broccoli close enough under a microscope, you’d see amino acids (which make up protein), fatty acids (which make up fats), and various sugars, starches, and fibers (which make up carbohydrates).

Energy is required to keep these chemical bonds intact.

But after you eat them, your body’s metabolism takes hold.

Once these molecules get shuttled into your cells, cellular respiration occurs and, through several chemical steps, systematically breaks apart some of these chemical bonds to create new molecules.

As these chemical bonds gets broken apart, energy is released.

But if that was all that would happen, your body wouldn’t be able to make much use out of it.

So your body uses that energy in the formation of ATP. ATP now stores this energy for later in the form of new chemical bonds.

Now, ATP can run around and be used for different biochemical processes.

If your muscles need to flex, ATP comes in and breaks apart its bonds to release the energy required to do so.

Your lungs need to breathe? Same thing!

Which Foods are Calorie-Dense?

The calories in food come in different forms.

These forms take the shape of different chemical bonds. Each type of bond requires a different amount of energy, and therefore releases a different amount of energy during chemical reactions.

One of the easiest ways to categorize the calories is food is by macronutrients.

Protein, Fats, and Carbohydrates.

Proteins and Carbohydrates typically contain about 4 Calories for every gram of food.

Although, fiber is an exception. Your body cannot metabolize fiber on its own. Some fiber gets digested by your gut bacteria, allowing you to derive around 2 Calories per gram, while some fibers can’t be digested at all. Just like water, they will pass through you without your body’s ability to break apart any bonds and derive any energy from them whatsoever. Learn more about your dietary fiber intake.)

Fats typically contain about 9 Calories for every gram of food.

Fat is therefore more calorie-dense. For every gram of food you eat, fats will contain more calories than proteins or carbohydrates.

The number of calories in foods high in fat will typically be much more calorie-dense.

Foods that have a low calorie-density, like many fruits and vegetables, also tend to have high water and fiber content.

This is one of the reasons these foods can be effective for weight loss.

How should you think about calories when thinking about your diet?

There are different schools of thought when thinking about the calories in food.

For some, learning about the calories in food can help them better understand how much they’re eating. Particularly if they are tracking it over time.

Others pay it little heed to these numbers and don’t see much of an improvement to their health or waist line.

Others still may becomes too caught up with the calories in food and become a source of anxiety.

If you fall into this latter camp, it is best to pursue different strategies when seeking a healthy diet.

For those who don’t see much of an improvement, it is possible that a deeper understanding or a better way of interpreting your caloric consumption may still help.

And for those who find it truly helps them with their nutritional health, this knowledge can be game-changing.

A good place to start is through our simple, step-by-step guide to tracking your macronutrients!


Recent Posts

See All


bottom of page