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The Truth About Calories

Posted by Mariana Silva on 26-10-2026

Odd News

Counting calories might seem straightforward, but new research suggests that the numbers printed on food labels do not tell the whole story. Scientists at Arizona State University have developed a mathematical model showing how gut bacteria influence the amount of energy people obtain from their meals.

Published in PLOS One (2026), the findings suggest food composition, fibre and microbial activity significantly affect calorie absorption; in a controlled study, fibre-rich diets led to about 116 fewer calories absorbed daily than a typical Western diet.

Why Food Labels Miss The Full Picture

Traditional calorie calculations rely on a system developed more than a century ago. Known as the Atwater system, it estimates food energy using average values for carbohydrates, proteins and fats. Although widely used, this approach does not fully account for the complex interactions between digestion and intestinal microorganisms.

Gut bacteria process substances that escape digestion in the small intestine, transforming some of them into compounds the body can absorb.

This means the energy people obtain from food can vary depending on what they eat and how their digestive system processes it.

What Scientists Discovered About Fibre

Researchers examined a controlled dietary study comparing two eating patterns. One diet included substantial amounts of fibre, resistant starch and minimally processed foods. The other resembled a conventional Western diet, containing more processed foods and less fibre.

Participants following the Western-style diet absorbed approximately 116 additional calories each day. Interestingly, those consuming more fibre did not report feeling hungrier. The results suggest that dietary composition can influence energy absorption independently of perceived appetite.

Gut Bacteria Provide Unexpected Energy

To understand these differences, researchers developed the Digestion, Absorption and Microbial Metabolism model, known as DAMM. The model estimates how food is processed throughout the digestive system, including the contribution of intestinal microorganisms. Gut bacteria ferment certain carbohydrates and fibres, producing short-chain fatty acids that the body can absorb.

According to the calculations, these compounds supplied approximately 140 calories daily, representing around 7.4% of usable dietary energy.

Overall, the model estimated that roughly 85% of usable energy was obtained in the upper digestive tract, with approximately 15% associated with processes in the lower digestive tract.

Why More Fibre Can Mean Fewer Calories

The findings revealed an interesting relationship between microbial activity and energy absorption. Participants consuming fibre-rich foods produced more short-chain fatty acids, indicating increased microbial fermentation. However, they still absorbed fewer calories overall.

This happens because additional energy generated by bacteria does not necessarily compensate for differences in the amount absorbed earlier during digestion.

The findings demonstrate why focusing exclusively on the calorie values printed on packaging can overlook important biological processes.

Could This Change Nutrition Advice?

The new model produced estimates that more closely matched observed energy absorption than conventional calculations. Researchers believe the approach could eventually improve understanding of obesity, diabetes and other metabolic conditions. It may also contribute to personalised nutrition strategies that consider interactions between diet and gut microorganisms. However, further studies are needed before the model can be used to develop individual dietary recommendations.

For now, the findings highlight an important principle: the nutritional value of food depends on more than its listed calories. Its composition, processing and interaction with the gut microbiome also influence how the body uses energy.