studies

About ten years ago I started working out for the first time in my life, and with it, paying attention to the food I put in my body for breakfast, lunch, and dinner. I never knew much before that about calories, other than the tired "2000 a day" guideline. I could hardly tell you about macronutrients, or how much protein an active person should get. And so, later in my life, I had quite an education.

But there's still a lot that I don't know, apparently, because it wasn't until very recently that I learned where calories come from; or rather, how they're tallied up for inclusion on a food label. Of course, I am familiar with the idea that you can always count up the different ingredients in a meal and their known nutritional values. For example, if you're baking, it's easy to find out the calories in one cup of flour, a tablespoon of sugar, and so on.

But how are the calories in base foods even calculated? And furthermore, how do we know for sure how much protein, fat, or carbs are in certain foods?

It "blew" my mind when I learned that food scientists have a fascinating process for determining the amount of energy contained in different foods. It involves a strange machine called a "bomb calorimeter."

  An old bomb calorimeter from the 1960sSeth/Flickr

We all know that food gives us energy, but you've likely never thought of food energy in the same terms as the other different forms of energy like lights, heat, electricity, etc. I know I had never thought of it like energy energy.

But that's exactly what it is, and calories are a very specific measure of that energy.

So in order to determine how many calories are in a certain food, ingredient, or meal — get this — scientists literally blow it up and measure the results of the explosion.

How cool is that!?

In the video below, scientists from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University show the fascinating process from start to finish.

In the experiment, the team prepares a Christmas dinner plate of turkey, gravy, and potatoes. The first step to determining the calories in the meal is to "homogenize it" or blend it into smithereens, destroying any large chunks and turning the meal into a smooth, near-liquid. Yum!

"Then, over the course of three days we slowly remove all the moisture from it in a freeze drier," says Dr. Sue Roberts. Imagine turning that gooey slop into something similar to the consistency of astronaut food.

The dried samples are then compressed into extremely dense pellets about the size of a Tums antacid.

Now here comes the Parr 6200 "bomb" calorimeter. The very precisely measured pellet-ized portion of the original dinner is put into a chamber and lowered into some water inside the machine. An electrical charge is then applied to the food to "explode it."

Why the water? The calorimeter is able to measure the exact temperature of the water before and after the food explosion. When you look at the actual definition of a calorie, which according to Merriam-Webster is: "the amount of heat required to raise the temperature of one kilogram of water one degree Celsius," it all starts to make sense. Take the temperature of the water after the explosion and you can determine exactly how much energy was contained in the food pellet based on the temperature increase. Amazing!

  - YouTube  www.youtube.com  

The calorimeter first came about in the 1800s. Even then, our understand of heat, energy, and food science was extremely limited.

As recently as the 1700s, scientists generally believed heat was made of some kind of weightless gas, which they called "caloric."

The theory was disproven in 1799 when Sir Humphrey Davy, an English chemist, rubbed two pieces of ice together in a vacuum (which contains no air or gas) and was able to generate friction heat, thus melting the ice. It was roughly around the same time that Antoine Lavoisier and Pierre Simon de la Place developed the first calorimeter.

Calorimeters, and the Calorie itself, weren't regularly used for food until the late 1800s.

As cool as it is (and it is extremely cool) exploding food in a bomb calorimeter isn't the most common practice today.

Frankly, it's usually not necessary when you can estimate nutritional values in other ways. More common today is the Atwater System, which estimates calories based on the nutritional breakdown of a food item as such:

• Four kcals (calories) for one gram of protein
• Four kcals for one gram of carbohydrates
• Nine kcals for one gram of fat
• Seven kcals for one gram of alcohol

Carbs are the most complicated and thus are often measured by subtracting the percentage of proteins and fats. The remainders, by definition, should be carbohydrates.

  This food is on FIRE!  Giphy  

And, of course, bomb calorimeters have lots of different uses besides determining the calories in the newest line of flavored Doritos. They can be used to test the energy potential of alternative fuels, find more efficient animal feeds, and analyze samples of oil or coal for their potency.

Understanding this process kind of changes the way I look at food. You can't really see the energy in a bag of chips, let's say, but maybe you can imagine the way it might heat a pot of water if it exploded! It makes the numbers on the back of a nutritional label a little more tangible and real, and can maybe lead to more mindful and intuitive eating practices.

Ultimately, though, there is so much more to food than the calories it contains. There are the nutrients, like the proteins, carbs, and fats — the micronutrients like vitamins and minerals that our bodies need. Some people like to know as little as possible about the inner workings of our food and focus purely on their enjoyment of the making, eating, and sharing. But if you're like me, you like to know the science behind food production, and how and why food powers our bodies the way it does. That's all part of the fun.