Call for new calorie counting – dieters misled
Dieters have been misled by the outdated system for assessing the calorie content of food for decades, according to US research that could redefine how people attempt to lose weight.
People who eat high-fibre foods such as vegetables and muesli are consuming more calories than they think because food labels do not take into account the calories in fibre.
Meanwhile, the system over-estimates, by up to 20%, the content of some protein-rich foods such as tuna steak that can take more energy to digest than simple carbohydrates like white bread.
The scientists behind the research also reveal that consumers could reduce their calorie intake by eating raw rather than cooked foods.
They argue that the way calories are assigned to foods by manufacturers needs a significant overhaul because they are 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,” Professor Richard Wrangham, a primatologist at Harvard University, says.
He says the public is being given “erroneous information about the energy value of many foods”.
Prof Wrangham raised the issue at the annual meeting in Boston of the American Association for the Advancement of Science.
Apart from under-estimating the calorific value of fibre, 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 a century, the energy value in foods has been calculated using the Atwater system.
In general terms, this system means that a gramme of protein or carbohydrate provides four calories, while a gramme of fat provides nine 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.
“The Atwater Convention yields realistic values for foods that are highly digestible, such as white bread,” Prof Wrangham says. But the system leaves out fibre – assuming that this component of food has no energy value to the body.
Raw foods, he adds, are also systematically less energy-producing than the same foods cooked, but regulators that collate data from relevant laboratories do not reflect these differences.
“There are two basic reasons why raw foods provide less calories than cooked foods – they are less digestible and also the bits that can be digested cost more to break down. We are talking at least a difference of between 10% and 30%.
“So eating raw food is a good way to lose weight, but you need to be careful about it long term and it would not be advisable in children.”