One recent study found that a packet of almonds labelled as 170 calories was in fact just 129 calories, while many sugary cereals have more calories than the labelling specifies. This is because the number of calories we absorb from food depends on a number of factors, including our own metabolisms, the way the food is cooked, how much fibre the food contains, and how much the food is chewed.
Because the current calorie labelling system ignores the energy content of fibre, people unknowingly consume many more calories than they thought in high fibre foods such as muesli and porridge. Researchers say the average bowl of bran cereal actually contains 20 more calories than stipulated on the label.
In contrast, calories in protein foods have been exaggerated by up to 20% because the system does not subtract the number of calories it takes to chew.
Another study found that cooking can add calories to food. Mice given raw sweet potato lost over four grams of weight, while those given the same amount of cooked sweet potato gained weight.
Calorie consumption also depends on the individual. We all have varying levels and types of bacteria in our guts. Biologist Rob Dunn from North Carolina State University believes obese people could have an abundance of certain types of bacteria in their guts which makes them more efficient at absorbing calories.
Writing in the journal Scientific American, he said: “In the end, we all want to know how to make the smartest choices at the supermarket. Merely counting calories based on food labels is an overly-simplistic approach to eating a healthy diet – one that does not necessarily improve our health.”
He believes a better way to avoid putting on weight is to stick to natural, raw and unprocessed foods which take longer to digest. For example, a cheese sandwich made with whole grain bread contains 10% fewer calories than a cheese sandwich made with white bread, because whole foods are more difficult to digest.
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