How Many Calories Have You Burned

Updated: Feb 16

If you’ve ever been to a group fitness class where everyone’s heart rates and estimated calorie burns are displayed on a screen, you know that these statistics vary greatly from person to person. You’ve probably also noticed that, generally, men tend to burn more calories than women. But have you ever wondered why different people burn calories at such different rates, even during the same workout?

RELATED: Can Calorie Counting Help You Lose Weight?

The truth is that metabolism — an umbrella term for all the processes in your body that break down nutrients for energy, fuel growth, and more — is far from simple. “There is a constant ebb and flow of reactions that build or repair our body (anabolism) and reactions that break down food and energy stores for fuel (catabolism),” says , a virtual functional medicine practitioner based in New York City. “It is an extremely complex topic that is very challenging to research,” she adds. Various factors play into how fast or slow you’re burning calories at any given time. Here are the six that experts say have the greatest impact on how many calories you burn while working out.

1. Body Weight

“Generally, the more you weigh, the more calories you’ll burn per session,” says Kyle Gonzalez, a San Francisco–based certified strength and conditioning specialist and performance coach at . “Calories are just a measure of energy, so the more you weigh, the more energy it takes to move your body.” Put differently, of two people with different weights, the one who weighs more will burn more calories, because they have a greater energy expenditure when moving.

People with larger bodies also tend to have larger internal organs (such as the heart, liver, kidneys, and lungs), which is a significant factor in how many calories are burned during exercise and at rest, because these organs and their processes require energy. One study found that up to 43 percent of the variation in total calorie burn between people could be explained by differences in the size of their internal organs.

This is one of many reasons that weight loss is so complicated — your body burns fewer calories as your weight decreases, which can lead to a weight loss plateau or even regaining weight. That said, it’s not the only reason. A previous review explains that weight loss can trigger other physiological adaptations as well, including the body’s tendency to burn stored fat for energy, a process called fat oxidation; greater hunger, due to higher levels of the hormone ghrelin; and less satiety, as levels of the hormone leptin dip.

If you’re looking to lose weight and have hit a plateau, consider working with a registered dietitian who specializes in weight loss and can help you meet your goal in a healthy and sustainable way. Find one at the Academy of Nutrition and Dietetics.

Also, keep in mind that exercise is a boon for overall health regardless of whether you lose weight. A review published in October 2021 in iScience suggests that while increased exercise doesn’t typically lead to long-term weight loss, improved cardiorespiratory fitness is associated with better health outcomes and a lower risk of premature death, regardless of weight.


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