In many cases, no, calorie counts on food labels cannot be trusted, and for more reasons than one.
In this New York Times Op-Doc, filmmaker Casey Neistat shows just how unreliable they can be. Enlisting the services of a science lab equipped with a calorimeter, he tested five random samples selected from among foods he might eat on any given day. Four of those five had more calories than their labels said they did, including a pre-packaged spicy tofu sandwich that had nearly double the amount. A Subway sandwich was the only one that came in under the stated calorie count.
Some scientists are also questioning the very system we use for measuring calories in foods, the century-old Atwater system that assigns 4 calories per gram for proteins and carbohydrates and 9 calories per gram for fats. That system does not take into the account the fact that the degree to which our bodies metabolize foods varies with the type of food, the level of processing it has undergone and the “energy status” of the person eating it.
For example, some of the fat in almonds and certain other nuts goes undigested and passes through our bodies as waste. A 2012 study led by USDA scientist Janet Novotny found that the calories we get from a one-ounce serving of almonds is 32 percent less than the Atwater values estimate. So when you eat a large handful of almonds, you may only be taking in 109 calories as opposed to the 161 calories listed on the label. As NPR reports, scientists suspect that this is because we don’t chew them enough to fracture all the cell walls and release all the fats.
Food processing also affects the number of calories we actually absorb from a food. Rachel Carmody, a postdoc at Harvard University who organized a symposium called “Why a Calorie Is Not a Calorie and Why It Matters for Human Diets” at the American Association for the Advancement of Science’s annual meeting last month, told NPR that she wants people to “realize that something that’s more highly processed is going to represent more calories than in a less-processed form.”
Based on experiments conducted in her lab, she attributes the net energy gains “to higher rates of nutrient assimilation in the small intestine as well as reduced diet-induced thermogenesis, the metabolic cost of digestion.” It is a lot easier for our bodies to extract nutrients and calories from cooked and processed foods than from whole and raw foods, and those foods also require less energy for our bodies to digest.
These aspects of digestion are not represented in the Atwater factors typically used in the determination of metabolizable energy value. Thus researchers who report Atwater-based energy values as well as consumers who utilize nutrition labels to manage their caloric intake will necessarily underestimate the energetic gains associated with a processed diet.
Still, other experts like Malden Nesheim and Marion Nestle, co-authors of “Why Calories Count,”¯ argue that “for most foods, estimates based on Atwater values are close enough.” And “until research convinces us otherwise, we believe a calorie is a calorie.”
An awareness of the calorie content in foods is supposed to help us make more informed choices and perhaps cut back a bit on what we eat. That’s the point of the new federal requirement that calories be posted at food establishments across the country, which is expected to go into effect at some point this year. We’ll have to wait and see whether or not across-the-board calorie labeling will help Americans lose weight or improve health outcomes. But if it’s going to do any good, as suggested in the Op-Doc, don’t we at least have to start with calorie counts that are a little more reliable?
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