Tuesday, October 14, 2003

A Calorie is a Calorie is a Calorie

I don't want to get into the diet wars here, but one thing which has always puzzled me is why nutritionists have clung to this little article of faith. I'm starting to wonder if they're particularly bright people. Consider this article about the Atkins diet:

Now, a small but carefully controlled study offers a strong hint that maybe Atkins was right: People on low-carb, high-fat diets actually can eat more.

The study, directed by Penelope Greene of the Harvard School of Public Health and presented at a meeting here this week of the American Association for the Study of Obesity, found that people eating an extra 300 calories a day on a very low-carb regimen lost just as much during a 12-week study as those on a standard lowfat diet.

Over the course of the study, they consumed an extra 25,000 calories. That should have added up to about seven pounds. But for some reason, it did not.

So, it's one study and it needs to be replicated. It may or may not hold up, but then consider this:

That strikes at one of the most revered beliefs in nutrition: A calorie is a calorie is a calorie. It does not matter whether they come from bacon or mashed potatoes; they all go on the waistline in just the same way.

Not even Greene says this settles the case, but some at the meeting found her report fascinating.

"A lot of our assumptions about a calorie is a calorie are being challenged," said Marlene Schwartz of Yale. "As scientists, we need to be open-minded."

Others, though, found the data hard to swallow.

"It doesn't make sense, does it?" said Barbara Rolls of Pennsylvania State University. "It violates the laws of thermodynamics. No one has ever found any miraculous metabolic effects."

Look, this doesn't violate any laws of thermodynamics. The issue is not whether a measure of energy, a calorie, is the same regardless of the form it's stored in, the question is whether or not the form it is stored in has any impact on the way your body processes it. Not all food has to be completely digested. Perhaps some types of food require more energy to be digested. Maybe some types of food have an impact on your metabolism somehow. Who knows? But to take it on faith that it shouldn't make any difference is really quite odd.