Not all calories are equal, researchers say, urging quality over quantity

Processing, cooking, even ripeness alter how the body uses energy

BOSTON (AP) — The common wisdom that weight loss boils down to a simple equation — consume fewer calories than you burn — doesn’t capture the full picture, according to physicians and researchers who study metabolism.

Dr. Dariush Mozaffarian, a cardiologist and director of the Food is Medicine Institute at Tufts University, said that “different foods have very different effects on the brain, liver, fat cells, muscle function, pancreas and all organs related to metabolism and body weight.”

A calorie is the unit of energy the body can extract from carbohydrates, proteins, and fats, but the body does not process all calories the same way. The complexity recently became a public issue when a lawsuit accused the maker of David protein bars of mislabeling calorie counts based on bomb calorimetry, which measures energy by burning food. The lawsuit was later dropped. The company’s numbers were based on the calories the body can actually use, which experts said is the only figure relevant for diet.

“You could put sawdust into a bomb calorimeter and you would get basically 4 calories per gram,” said Dr. David Ludwig, an endocrinologist and researcher at Boston Children’s Hospital. “If you’re a termite, yes, you’ll get calories from it. But humans won’t.”

Calorie counts on nutrition labels reflect the total the body is likely to metabolize, but because of permitted rounding, the numbers can be off by as much as 20%. Factors including how a food is cooked, how processed it is, the digestibility of its ingredients, and variations in an individual’s genetics and sleep all affect calorie absorption.

High-glycemic foods such as white breads, pastas, and sugars are easily converted into usable energy and trigger the body to store fat, Ludwig said. Foods containing resistant starches — such as beans, whole grains, and seeds — resist that conversion and do not trigger the same storage response.

“Having a snack of 8 ounces of sugary beverage, 100 calories, should be better for your weight than 1 ounce of nuts at 200 calories, right?” Ludwig said. “That’s the opposite of what actually happens because those 100 calories, even if they’re fewer at that moment, they shift your body toward storing fat and leave you hungrier sooner.”

Even simple preparation changes the equation. The calories in cooked foods are more easily absorbed than those in raw ingredients, and the calories in unripe produce such as bananas are less easily absorbed than when the fruit is ripe. Grinding food can also change its caloric impact.

“One classic example is that the calories in whole almonds are absorbed substantially less well than the calories in almond butter,” Ludwig said. “Just processing the almonds into almond butter causes a change in how much they will be absorbed.”

Diets high in ultra-processed foods reduce the number of calories the body burns at rest, according to Mozaffarian, meaning a higher proportion of those calories are stored.

Dr. Fatima Cody Stanford, a Harvard Medical School obesity specialist, noted that genetics lead individuals to process calories differently, and even a bad night’s sleep can change how the body handles the same food.

Researchers said calorie counts can still serve as a rough guideline but that the evidence suggests people should focus on diet quality, not just calorie quantity. They recommended avoiding ultra-processed foods, particularly refined starches, and building diets around whole, minimally processed foods rich in plant-based fiber.

“We need to think about calories in a much more sophisticated fashion than the number on the package,” Ludwig said. “The number on the package can do more harm than good by misleading people into thinking that it’s simply an accounting problem.”