Look anywhere in the grocery store and you will see calories. Not just because they are in the food, but they are also on it. Pretty much every single food item has a label that lists how many calories it has in each serving. Even outside of the grocery store, everything from a restaurant chain to a gas station franchise has caloric values listed on their foods.
Most of us take this information for granted, and according to a 2006 article published in The American Journal of Clinical Nutrition, a whopping 58% of consumers consider calorie labels when making purchasing decisions at the grocery store. Given how important calorie labels have become to the average person and their dietary decisions, I think that it is important to ask how exactly calorie labels calculate calories.
How?
Well at first glance it seems really simple: most calories are calculated using the Atwater System, which stipulates that there are 4 calories in every gram of protein, 9 calories in every gram of fat, and 4 calories in every gram of carbohydrates.
So, if your slice of cake contains 7 grams of fat, 30 grams of carbohydrates, and 4 grams of protein, then you have approximately 199 calories in that slice of cake.
So that’s it then?
We just follow a formula to determine the number of calories there are in foods.
Pretty neat… Until
How do you know how many calories are in that banana?
It makes sense to use the Atwater System to calculate calories in artificially made foods, but how do you know how many calories there are in something that grows out of the ground?
To answer this, we have to break down what a calorie is to its fundamental.
A calorie by definition, is a measurement of energy. More specifically, it is a measurement for how much energy is needed to heat up a single gram of water by 1 degree Celsius.
With that in mind, the answer becomes surprisingly novel: we burn the food. An age old technique of heating up water to create energy is our answer to figuring out how much energy is in our food.
In this case, a banana would be placed in an insulated, oxygen-filled chamber, called the bomb calorimeter, which is surrounded by water. The banana would be ignited using an electrical current and completely burnt, which will increase the temperature of the water surrounding the chamber. This increase in water temperature is then measured, and for every degree of temperature increase, the banana will be labeled as having that many calories. For instance, if the banana’s burning increases the water temperature by 40 degrees, then the banana contains 40 calories.
Why?
As for why pretty much every single thing between a hotdog at Costco and a bottle of water in a vending machine has calories listed – it’s because of the Affordable Care Act of 2010 and the Nutrition Labeling and Education Act of 1990.
The Nutrition Labeling and Education Act of 1990 mandated calorie labels on most packaged foods starting in 1994, but exempted restaurants and other food places. The Affordable Care Act made it so any restaurant chain with more than 20 locations must list calorie counts on menus and menu boards.
Implications
Okay so now that we realize how we got here, how serious should we really take them?
Your coworker Dave, who is on his sixth attempt at a diet, might view the caloric count on packaging as the word of the messiah, but in reality, it isn’t set in stone. Yes, calories are measured pretty accurately in the era of Ozempic and gym memberships, but just because a food item has a certain number of calories, doesn’t mean your body absorbs it all.
Calorie absorption varies based on a myriad of things such as food type, metabolism, and even gut health. That’s right, if you’re feeling real hungry after your 8th visit to Dave’s hot chicken this week, it’s probably because the microbes in your gut are too busy being cremated to digest and absorb that extra hot slider.
Even how you chew your food directly affects the caloric intake of your body. For instance, a study from the Journal of Nutrition published in September 2008 found that the calories in whole nuts aren’t absorbed well because of their tough cell wall, which contains fat. If not properly broken down by chewing, a considerable number of calories are never absorbed, and are excreted as waste instead.
Ultimately, caloric labels are an estimate, meant to be a guideline on dietary choices for the average person. So I guess as is the case with most other things, take it with a grain of salt.