PITTSBURGH (KDKA) — If you’re counting calories, you may be off a bit.

Calories are determined in a lab by how much energy it takes to burn up a food, with a calculator, adding up grams of carbohydrate, protein and fat.

“Because we know how many calories per gram each of them have,” dietician Heather Mangieri, of Nutrition Checkup said. “They treat all foods equal, which is where I think some of the problem comes in.”

A Harvard researcher points out not all measured or calculated calories are used by the body, because the process of digestion wastes some, for example, foods rich in fiber, also vegetables, fruit, beans and nuts.

She also says some foods have more calories than what might be on the label, just because of how it is prepared.

For instance, a pureed carrot yields more calories than a raw carrot, because pureeing takes some of the work out of digestion.

“It encourages people to eat more whole, natural foods, which we’re already trying to get people to do, so that’s great,” Mangieri continues.

The biggest difference is for starchy foods, such as potatoes, bread and rice, which can be up to 30 percent off.

The most accurate calorie counts are on meats, which are only three percent off.

“I don’t think in the big picture it matters because it’s all an estimate,” Mangieri said. “We suggest 3,500 calories equals one pound, there’s even question nowadays whether that’s accurate. So we’re going to overestimate sometimes, we’re going to underestimate some times, but in the end it all does kind of equal itself out.”

The current method of figuring out calories is about a hundred years old.

While it might be time for an improvement to help people figure out how many calories they should have in a day, changes won’t be so simple.

People are all different when it comes to how they process what they eat.