Have we been miscounting calories?
When it comes to weight loss, a calorie is a calorie is a calorie. That’s been the mantra of nutritionists, dietitians and food regulators in the United States and Europe for more than a century. But when it comes to comparing raw food with cooked food, or beans with breakfast cereals, that thinking may be incorrect. That was the consensus of a panel of researchers last Monday who listed the many ways that the math doesn’t always add up correctly on food labels.
“Our current system for assessing calories is surely wrong,” said evolutionary biologist Richard Wrangham of Harvard University, the co-organizer of the panel.
In a discussion of how food is digested in everything from humans to rats to pythons, the panel reviewed a spate of studies showing that foods are processed differently as they move from our gullet to our guts and beyond. They agreed that net caloric counts for many foods are flawed because they don’t take into account the energy used to digest food; the bite that oral and gut bacteria take out of various foods; or the properties of different foods themselves that speed up or slow down their journey through the intestines, such as whether they are cooked or resistant to digestion.
The process used to estimate calories for food was developed at the turn of the 20th century by Wilbur Atwater. It was a simple system of calculating four calories for each gram of protein, nine calories for each gram of fat, and four calories for each gram of carbohydrate (modified later by others to add two calories for a gram of fiber). Although it has been useful for approximating the energetic costs of metabolizing many foods, its shortcomings have been known for decades-and some nations, such as Australia, have dropped the system because it is “inaccurate and impractical,” said panelist Geoffrey Livesey, director of Independent Nutrition Logic Ltd. in Wymondham, U.K..
One key area where the system is inaccurate, Wrangham reported, is in estimating the calories for cooked food. Cooked items are often listed as having fewer calories than raw items, yet the process of cooking meat gelatinizes the collagen protein in meat, making it easier to chew and digest – so cooked meat has more calories than raw.