Dr Giles Yeo, a geneticist at Cambridge University in the UK, has written a new book in which he makes the case that the current approach to understanding calories is "entirely wrong".

In his book Why Calories Don’t Count, Yeo, who has been researching obesity and its causes for more than 20 years, writes that rather than focusing on how many calories a food contains, the emphasis should be on its “caloric availability".

This, Yeo says, is the measure of how many of the calories in a food are available for the body to absorb.

"Don’t blindly count calories – because all foods have levels of different caloric availability," Yeo says.

"This is the number of calories digestion can extract from a food, versus the number of actual calories in that food.

"Every calorie might be equal, but some are more equal than others.

"For example, the caloric availability of protein is 70 per cent, meaning we absorb, on average, 70Kcal for every 100Kcal we eat. This is different from the more than 95 per cent we absorb when it comes to carbohydrates and fats."

According to Yeo, this could – and should – have a bearing on weight loss guidelines, which almost always use calories as a simple measure of how much energy we’re consuming.

Yeo points out that, while calories are a useful measurement, the simplistic approach that the more calories an individual consumes the more weight they will gain is "outdated".

The relationship between calories and "caloric availability" could partly explain research results, which have shown that people who consume the same number of calories – but acquire them from different foods – put on different amounts of weight.

For example, a study conducted by the National Institutes of Health showed that people eating ultra-processed foods gained more weight than when they ate a minimally processed diet.

The difference occurred even though meals provided to the volunteers in both the ultra-processed and minimally processed diets had exactly the same number of calories and macronutrients.

To read more about Giles Yeo and his research, click here. To find out more about his latest book, click here.