How Are Calories in Food Measured?

How do food manufacturers measure the calories in food? How do they know what to put on nutrition labels? Ask Science discusses several methods of calorie measurement (and explains why they're all problematic). 

Lee Falin, PhD
4-minute read
Episode #120

Do We Really Have to Burn Food to Measure Calories?

Well, no. While the above method does give you the true amount of calories in a candy bar, it doesn’t give you the full amount of calories that your body gets from the candy bar. That’s because not all of the food you eat is metabolized by your body. Some of it (such as fiber) is lost in the form of waste.

So food labels use one of two methods to measure calories. Method one is to use what is called the Atwater system, which involves a bunch of mathematics to determine how much energy is in each gram of fat, carbs, and protein in a food, then subtracts how much of those calories are expected to be lost in bodily waste. However this is both somewhat tedious and has been shown to be rather inaccurate.

The FDA also allows a simpler method for food manufacturers. They can look at their ingredients and determine how many grams of fat, carbohydrates, and protein they contain, and then assume that each gram of protein and carbohydrates gives 4 kilocalories, while each gram of fat gives 9. Then you subtract 4 kilocalories for every gram of fiber, and you have your official, government sanctioned calorie measurement.

How Accurate Is That System?

Now you might be wondering, after all of that scientific talk, how accurate is this 4, 4, 9 method? Well, not very. In fact, the higher the amount of fiber in the food, and the lower the fat, the more overestimated the calorie count tends to be.

Plus, not everyone’s body metabolizes at the same level of efficiency. Certain genetic conditions and illnesses can cause foods to be metabolized differently by some people than others, so what might be a 100 Calorie snack for you, might only be an 80 Calorie for your friend (or vice versa). And as Nutrition Diva taught us, all calories are not created equl.


So now you know more about calories (and Calories), how they’re calculated, and why you should pay even less attention to caloric estimates than you did before. Check out Nutrition Diva's show to learn more about how to maintain a healthy weight without counting calories.

If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com. If you liked today’s episode, you can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein.

Chocolate Bar image, meineresterampe at Pixabay. CC BY CC CCO. Hamburger graphic courtesy of Shutterstock.




Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.