Counting Calories? The Body Calculates Differently by Jolien Durwael

You're standing in the supermarket and turn a package around. 200 calories per serving. Clear enough, you think. That's what your body will soon take in. But the human body doesn't work that simply.

The calories listed on a nutrition label are not exactly the same as the energy your body ultimately absorbs. How much energy we actually obtain from food depends on several factors: the composition of the food, how our body digests it, how much we move, and even the bacteria in our gut.

In other words: the body calculates differently than the label.

How calories on nutrition labels are calculated

Most nutrition labels are based on the Atwater system, a method that has been used for more than a hundred years to calculate the energy value of food.

According to this system:

1 gram of carbohydrates provides about 4 kcal

1 gram of protein provides about 4 kcal

1 gram of fat provides about 9 kcal

1 gram of alcohol provides about 7 kcal

This method is useful for comparing foods, but it takes limited account of how our body actually digests and processes food in reality.

Fiber: energy your body does not fully use

Technically, fiber belongs to the carbohydrate group, but our body cannot break it down very well on its own.

Part of the fiber is fermented by gut bacteria in the large intestine. This process does release some energy, but a large portion of fiber passes through the digestive system without providing much energy.

As a result, fiber-rich foods often deliver less usable energy in practice than the label suggests.

Protein: food that costs energy to digest

Proteins also behave differently than the classic calorie formulas suggest.

The body needs energy to digest proteins, absorb them, and convert them into usable building blocks. This is known as the thermic effect of food.

For proteins, this effect can reach 20 to 30 percent of their energy content. In other words, a portion of the calories from protein is already used during the digestion process itself.

Why two people get different amounts of energy from the same meal

There are also clear differences between individuals.

Research shows that factors such as:

• body composition
• hormonal balance
• physical activity
• and the gut microbiome

all influence how much energy someone actually extracts from food.

Two people can therefore eat exactly the same meal, yet absorb a different amount of energy.

The structure of food also makes a difference

Not only what you eat, but also how the food is structured affects how much energy becomes available.

A classic example is nuts. When you eat whole almonds, some of the fats remain trapped inside the nut's cell structures. As a result, they are absorbed less efficiently by the body.

In almond butter or finely ground nuts, those structures are broken down and the fats are released more easily. The body can then use that energy more efficiently.

This is also one of the reasons why highly processed foods often provide more available energy than the same food in its natural form.

What does this mean in practice?

Nutrition labels remain useful: they give a general indication of the energy content of food. But calories are not perfect mathematics.

The human body is not a calculator, but a complex biological system.

That is why nutrition scientists today increasingly look beyond calories alone, placing more emphasis on food quality, fiber, protein, and satiety.

Practical tips

A few simple insights can help:

• Choose unprocessed foods more often. Foods with an intact structure—such as vegetables, fruit, legumes, and nuts—are often less completely digested than highly processed foods.
• Eat enough protein. It not only promotes satiety but also requires more energy for the body to digest.
• Don't forget fiber. It supports the gut microbiome and leads to a slower release of energy.
• Keep moving. Energy expenditure depends not only on what you eat, but also on how active your body is.

Finally

The calories on a nutrition label are an average estimate. How much energy your body actually obtains from food depends on digestion, food structure, gut bacteria, and your own metabolism.

Or put differently: your body calculates differently than the label.

— By Jolien Durwael, Orthomolecular Nutritionist and author of Herstart.

Sources

Baer, D. J., Gebauer, S. K., & Novotny, J. A. (2016). Walnuts and almonds: bioaccessibility of energy and nutrients. Food & Function.

Nishi, S. K., Kendall, C. W. C., Sievenpiper, J. L., et al. (2021). Is a calorie a calorie? Almond bioaccessibility and metabolizable energy. Mayo Clinic Proceedings.

Kahleova, H., et al. (2019). The thermic effect of food: a review. American Journal of Clinical Nutrition.

Livesey, G. (2001). Accuracy of Atwater factors for calculating metabolizable energy. American Journal of Clinical Nutrition.