The system used for reporting the calorific value of food is out of date and misleads consumers, according to experts at the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston.
As an example, the experts noted that the calorie value of fibre is not included in calorie counts – causing those following a high fibre diet to consume more calories than they think.
Another example is that some protein-rich foods such as tuna steak use more energy to digest than simple carbohydrates such as bread.
There is also, noted the experts, typically a difference between raw and cooked versions of the same food in terms of their calorie count – the former being generally lower, by up to 30%.
The current system, which has been used for over 100 years, both overstates and understates calorific content. Known as the Atwater system, it uses average values such as 4 Kcal/g for protein, 4 Kcal/g for carbohydrate, 9 Kcal/g for fat and 7 Kcal/g for alcohol. Thus a food containing 15 g of fat, 20 g of protein, 30 g of carbohydrate would be ascribed a calorie value of (15 x 9) + (20 x 4) + (30 x 4) = 335. Any fibre contained in the food would not contribute to its calorie count, as the Atwater system does not define the calorific value of fibre.