Dieters who eat high-fiber foods, such as vegetables and muesli, in an attempt to lose weight often consume more calories than they think because current food labels do not factor in the calories in fiber, according to new research presented at the American Association for the Advancement of Science (AAAS).
The findings also suggest the current labeling system, based on the Atwater Convention, overestimates the content of some protein-rich foods that can take more energy to digest than simple carbohydrates by up to 20%.
"The Atwater Convention yields realistic values for foods that are highly digestible, such as white bread," said Richard Wrangham, a primatologist at Harvard University. “But the system leaves out fiber—assuming that this component of food has no energy value to the body."
As reported by the Guardian, the researchers also found consumers could reduce their calorie intake by eating raw rather than cooked foods. They said the way calories are assigned to foods by manufacturers needs a significant overhaul because calories are currently both over and under estimated by up to 25%.
"There is a lot of misinformation around calories, and it is crucial for the consumer, whether they are on a diet or not, to have the correct information about what they eat," Wrangham added.
He said the standard system also does not take into account the way foods are prepared and eaten. The calorie contribution from raw and cooked versions of the same food are different for example, but that is not reflected on food packaging.
For more than 100 years, calorie value in foods has been calculated using the Atwater system. "Nutritionists calculate the calorie values of individual foods by applying calorie conversion factors to each gram of protein, fat, and carbohydrate analyzed in foods," said British nutritionist Geoffrey Livesey, who also spoke on the AAAS panel.
Generally speaking, he said the system means 1 gram of protein or carbohydrate provides 4 calories, while 1 gram of fat provides 9 calories. Food manufacturers work out how much protein, carbohydrates and fat there is in a food and multiply up using the Atwater factors to get the total calories.
