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Fascinating article in New Scientist about the “calorie delusion.” Turns out that the number of calories listed on food labels can be very misleading, depending on the type of food:
[A]ccording to a small band of researchers, using the information on food labels to estimate calorie intake could be a very bad idea. They argue that calorie estimates on food labels are based on flawed and outdated science, and provide misleading information on how much energy your body will actually get from a food. Some food labels may over or underestimate this figure by as much as 25 per cent, enough to foil any diet, and over time even lead to obesity.
The standard figures assume that we get about 4 calories per gram of carbohydrate and protein, and 9 calories per gram of fat. But because of the way we digest food, more recent research suggests that’s an overestimate by about 20 percent for protein, and 25 percent for dietary fibre. Other factors like the texture of the food, whether it’s cooked, and even whether it’s chopped or ground up, also make a big difference.
In a study published in 2003, for example, a team led by Kyoko Oka at Kyushu University in Fukuoka, Japan, investigated the effect of food texture on weight gain. They fed one group of rats their usual hard food pellets, while a second group received a softer version. Both pellets had exactly the same calorie content and flavour. The only difference was that softer ones were easier to chew. After 22 weeks, the rats on the soft food diet were obese and had more abdominal fat. “Food texture might be as important a factor for preventing obesity as taste or food nutrients,” Oka and his colleagues concluded (Journal of Dental Research, vol 82, p 491).
The bottom line, as the article points out: don’t pick a brownie full of refined flour and sugar over a granola bar full of nuts and whole grains just because the label says the brownie has fewer calories.