The Calorie Myth

Calorie counting has become a religion in Western countries — but we’re getting it all wrong

Credit: Andrii Zastrozhnov/Getty Images

Here’s a recipe: Take one bad idea, coat it with a veneer of science, and chow down heartily. It may taste great but the long-term effects on your health include serious indigestion.

The bad idea in this recipe is the calorie. On the surface, calories seem straightforward. You use them to measure how much fuel you put in your body and how much energy you use when you walk, run, or even just sit on the couch breathing. If you pump your body full of calories and leave it idle, all that extra fuel sloshes around inside you. It doesn’t get used and instead, it becomes the fat that pads your skin and engulfs your organs.

This is more or less the central myth of Western diet. The word “myth” here doesn’t necessarily mean that calories aren’t real. It just means that calories are a story around which we organize our Western beliefs and values — just like ancient societies that had their own culture-shaping myths about why it rained and which spiritual beings ran the show.

But here’s the problem: If you take even a moment to learn about how the calorie was invented, how calories are measured, or what they actually represent, the whole story starts to unravel — fast.

Inventing the calorie

The calorie was created in the early 1800s as a unit of energy measurement. If you’re a science nerd, you already know about the kilowatt hour, a unit commonly used to measure electrical energy. You’ve also probably heard of the all-purpose joule, which is used for just about everything a physicist touches. The calorie was created as a convenient unit for measuring thermal energy (in other words, heat). By definition, one calorie is the energy it takes to heat a kilogram of water by one degree Celsius.

How can a unit that measures the change of water temperature tell you something about food?

(Technically, I’ve just described a Calorie with a capital C. The original calorie with no capital C is the energy needed to heat a measly gram of water. But outside of academic papers, no one uses the tiny lowercase calorie anymore. Because after all, do you want to eat a 452,000 calorie donut? For this story, we’ll be talking about the Calorie with a capital C.)

All of this doesn’t answer the obvious question, though: How can a unit that measures the change of water temperature tell you something about food? To answer that, we need the help of Wilbur Atwater, a chemist born in the mid-nineteenth century, shown below looking rather sedentary.

Photo via Wikimedia Commons

Atwater did something that sounds bizarre at best: He burned different types of food in a sealed chamber, which he submerged in a vat of water. This device is called, somewhat dramatically, a bomb calorimeter.

Basically, as your meal burns to ash in the bomb calorimeter, the temperature of the water around it increases. If you measure the change, as Atwater did, you can calculate, using calories, how much the burnt food warmed up the water. Assuming the human body is a similarly efficient food-burning machine, you can use this experiment to figure out how much energy the body can extract from, say, a bacon sandwich.

Diagram from the 10th Volume (second period of 1892) of the French popular science weekly ‘La Science Illustree’

If this process seems strange to you, that’s because it is. This was 1896, after all. Most doctors still thought attaching leeches to your body was a reasonably good way to cure herpes. But Atwater’s research with the bomb calorimeter had a lasting effect. It’s why we still talk about burning calories today.