Millions of people around the world use calorie counting as a way to manage what they eat and help them to lose weight. They count, and then reduce their calorific intake as a way to balance calories in with calories out. Can those millions of people be wrong? It turns out that the answer to that question is yes.

Our page on Dieting for Weight Loss talks about the idea that the key to weight loss is using more calories than you take it. It also describes this—accurately—as a myth.

This page discusses why calorie counting doesn’t work as a weight loss strategy. It also explores the thorny issue of food labelling, both calorie content and other nutritional information, and discusses why food labels and calorie counts can only ever be part of the story.

What is a Calorie?

A calorie (strictly speaking, a kilocalorie) is a measure of the energy in food (see box).

This may sound a slightly arbitrary definition—but it stems from the methods used to calculate the energy in food.

To measure calories, a measured amount of a substance is put into a piece of equipment called a bomb calorimeter, which has a central chamber surrounded by a litre of water. The substance is then burned until it is completely gone, and the temperature increase in the water is measured—hence the definition of a calorie.

If the temperature goes up by 5 degrees, the substance contains 5 calories.

In theory, you could then multiply up to work out how many calories are in the whole packet, and how many in an ideal serving.

However, it isn’t quite that simple, because scientists recognised many years ago that our bodies don’t necessarily use all the calories within a substance. We are not bomb calorimeters, and we don’t burn food in the same way.

Instead, the calories on food labels are actually calculated from the grams of carbohydrate, fat and protein within the product, using the formula:

• Nine calories are available for every gram of fat; and

• Four calories are available for every gram of carbohydrate or protein.

However, even this formula is potentially misleading.

Recent work has shown that the picture is actually considerably more complicated. Calorie counts, and even fat, carbohydrate and protein content, do not tell the whole story.

Food Structure and Calorie Availability

The structure of food has a huge impact on our ability to access and use the calories or energy within that food.

One of the best illustrations of this concept is almonds.

You can buy almonds in several forms, including whole, flaked, and ground. Nominally, 100g of each of these has exactly the same content in terms of calories, fat, protein and carbohydrate.

However, we absorb very different amounts of calories from the different forms.

The process of grinding up the nuts breaks the cell walls, which in turn releases lipids and other nutrients such as Vitamin E. This means that we can absorb more of the energy from the ground form—so the calorific intake is higher. When you eat whole nuts, chewing releases about 10% of the available energy. A further 60% is released through the action of enzymes in your digestive system. That leaves around 30% of the nominal calories in whole nuts unavailable to you. However, when you eat ground nuts, far more of that energy is available—over 90%, and possibly closer to 100%.

Generally speaking, when food is more processed, we can absorb the calories within it faster and more efficiently. Here the term ‘processing’ includes cooking, as well as mincing and grinding. This isn’t really about ultra-processed foods, but simply the ‘normal’ processes we use to make food more appetising and easier to eat.

Calories are generally harder to access in food that is closer to its natural state.

There is also increasing evidence that the whole of a meal is not the same as the sum of its parts when it comes to calories. In other words, structure is not just about processing, but also assembling.

For example, the calories that we take in from a cheese salad sandwich are likely to be different from the calories that we take in if we eat two slices of bread, some cheese, and some salad. The effect on our bodies is also likely to be very different (and our page on Sugar and Diet explains why the order in which you eat your food also matters).

The Importance of Individuality

The second issue that matters is that we are all individuals. We all deal with different foods in slightly different ways.

In particular, we all have a unique gut microbiome, which affects how we digest food (and for more about this, see our page on the Gut Microbiome).

Studies have found that if two individuals each eat a bag of nuts, one may be able to absorb roughly double the number of calories that the other one can access. Even if we were able to change food labels so that they took account of the processing that the product has undergone, the calorie count would still give you no information about how your own body would deal with the product.

Beyond Calorie Counting: The Effect of Food

We touched earlier on the effect of eating your food in different orders, and our page on Sugar and Diet explains more about this in terms of the effect on blood glucose levels.

However, the structure of food can also have an influence on the effect that food has on your body.

For example, one study compared eating whole or ground almonds, and looked at the effects over a period of 8 hours after eating the nuts. The researchers found that the people who ate the whole nuts had a 75% lower increase in circulating blood fats than those who ate the ground nuts. Circulating blood lipids have an effect on heart health, blood pressure and other markers of general health.

Similarly, there is a difference in blood sugar levels after eating large oats compared with eating finely ground oats.

This effect is not covered at all by food labels. However, it is worth considering, because the level of circulating blood lipids, and the speed with which your blood glucose levels rise and fall, both affect your health in significant ways.

---

In Summary

Food labels, and especially calorie counts, have come to be seen as extremely important in managing your diet. However, they only give a small part of the story.

The structure of food, and how we ourselves deal with that food, are significantly more important in terms of the energy that we can extract from our food.

A healthy diet generally means eating more fruit and vegetables, and preferably in less processed forms. We should also all be cutting down on the amount of ultra-processed food we eat. That means looking well beyond calorie counts and into more natural forms of foods—and those don’t come with calorie labels.

---