These are the 6 factors that can affect how many calories we burn

If you've ever been to a group fitness class where your heart rate and estimated calories burned are displayed on a screen, you know that these statistics vary greatly from person to person.

You've probably also noticed that, in general, 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?;

The truth is that metabolism—a general term for all the processes in our body that break down nutrients for energy, fuel growth, and much more—is not simple at all. There is a constant stream of reactions that build or repair our bodies (anabolism) and reactions that break down food and energy reserves for fuel (catabolism).

It is an extremely complex issue that is very difficult to research. Various factors influence how quickly or slowly we burn calories at any given moment.

6 factors that have a big impact on how many calories we burn 

1) Body weight

In general, the more someone weighs, the more calories they will burn per session. Calories are a measure of energy, so the more someone weighs, the more energy they need to move their body.

In other words, of two people with different weights, the one who weighs more will burn more calories because they expend more energy when moving.

People with greater body mass also tend to have larger internal organs (such as the heart, liver, kidneys, and lungs), which is an important factor in how many calories are burned during exercise and at rest, because these organs and their processes require energy.

It has been found that up to 43% of the variation in total calorie burning between people could be explained by differences in the size of their internal organs. This is one of the many reasons why weight loss is so complicated—our bodies burn fewer calories as our weight decreases, which can lead to a weight loss plateau.

Research has also shown that weight loss can cause other physiological adaptations, including the body's tendency to burn stored fat for energy, a process called fat oxidation. There is also increased hunger due to higher levels of the hormone ghrelin and less satiety as levels of the hormone leptin fall.

If you want to lose weight and have reached a plateau, consider working with a nutritionist who specializes in weight loss and can help you achieve your goal in a healthy and sustainable way.

Also, keep in mind that exercise is beneficial to your overall health regardless of whether you lose weight. A review published in October 2021 in iScience suggests that while increased exercise alone (without dietary intervention) does not 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.

2) Muscle mass

This is where things get a little more complicated. Someone with more muscle mass will burn more calories than someone else who weighs the same but has less muscle.

Muscle tissue burns more calories than fat tissue. However, claims about how many calories a pound of muscle will burn are often greatly exaggerated. In fact, evidence shows that one kilogram of muscle burns about five calories per day, while one kilogram of fat burns about two calories per day.

During exercise, having more muscle mass will increase your overall calorie burn because your body needs to produce more energy to support the increased rate at which your muscles are contracting.

In short, if you want to improve your calorie burn, consider adding strength training to your routine. Evidence shows that resistance training combined with aerobic exercise burns more fat than aerobic exercise alone and has more promising long-term results.

3) Gender

In general, men burn more calories at rest and during exercise than women. But there is nothing magical about why this happens—it is because men tend to have more muscle mass than women of the same age and weight.

Men generally burn 5 to 10 percent more calories than women at rest, and this percentage usually increases with exercise. And while women can certainly add muscle mass through strength training, physiological differences mean that, in general, women cannot do this to the same extent as men.

Women have a genetic predisposition to store more fat to support hormone production and childbearing. The U.S. Institute of General Medical Sciences explains that body fat is also necessary for functions such as energy storage, protection of internal organs, and support of basic functions such as growth, immunity, hormone production, reproduction, and metabolism.

The American Council on Exercise (ACE) reports that men need at least 21% to 51% body fat to support health, while women need at least 10% to 13%. But these minimum numbers may not be sufficient.

Although there is no official recommendation for the optimal body fat percentage, the most widely cited study on the subject suggests that a healthy range for adults under 40 is 8% to 20% for men and 21% to 33% for women. In general, the relationship between health and body fat is quite complex.

Instead of worrying about how our gender affects calorie burning, we should focus on things we can control. The bottom line is that men and women should focus on building muscle and improving cardiovascular health with a well-balanced program of cardiovascular exercise and muscle strengthening.

4) Age

As we age, we tend to lose muscle mass. After the age of 30, we begin to lose up to 3-5% of our muscle mass per decade.

The reasons for this are not entirely understood, but a review published in July 2017 in Aging Research Reviews explains that it is likely because our bodies become more resistant to the hormones that promote protein synthesis, which is key to maintaining muscle.

This loss of muscle mass reduces our metabolic rate—the speed at which we burn calories—at rest and during exercise. Although we cannot stop our bodies from aging, we can maintain or even increase our muscle mass with regular strength training.

Strength training can help us increase our resting metabolic rate, which helps us burn more calories at rest over time.

5) Level of physical fitness

The more we do a certain type of exercise, the easier it becomes. Our bodies actually adapt to make things easier over time.

Overall, this is a good thing. It means that we can run faster or for longer periods of time with practice, and that our muscles will be able to lift heavier weights with proper training. But it also affects calorie burning.

As our body adapts to training, we will burn fewer calories with the same workouts. From our lungs to our muscles, our heart, and our brain, your body becomes more efficient as we exercise.

This is why a beginner can burn significantly more calories than someone who has been doing the same workout for years – and that's why changing our workout routine can increase our fitness level and potentially increase the calories we burn.

6) Training Intensity

It is also possible that two people doing the same workout will burn different numbers of calories because they are not actually doing exactly the same workout. Someone who exercises at a high intensity may burn twice as many calories in the same amount of time as someone who exercises at a low intensity.

Just because you are covering the same distance as someone else, or doing the same movements, does not mean that you are both exercising at the same intensity.

While the U.S. Department of Health and Human Servicesexplains that walking and running offer the same benefits in terms of lowering blood pressure and reducing the risk of chronic conditions such as heart disease and type 2 diabetes, a previous study found that adults who walked one mile burned approximately 89 calories, while adults who ran the same mile burned approximately 113 calories.

A goal of 150 minutes of low-intensity exercise per week is enough to reap many health benefits, such as reduced stress, better sleep, lower blood pressure, increased cardiovascular capacity, and a reduced risk or slower progression of certain chronic conditions. Incorporating higher-intensity exercise into our routine will boost your calorie burn and further magnify these benefits.

The bottom line is that we should not worry about factors that are beyond our control. Exercise has countless benefits beyond simply burning calories, so the most important thing is to find types of exercise that we enjoy.

The type of exercise that is best for a person ultimately depends on their goals, physical condition, abilities, and, above all, what type of exercise they enjoy, so that they can stick with it and make exercise part of their daily routine.

By Vangelis Konstantopoulos, physical trainer