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?
It is an extremely complex topic that is very challenging to research as various factors play into how fast or slow you’re burning calories at any given time.
Here are the top 5 factors that can affect how many calories you burn
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 Future.
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 more energy.
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.
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.
2. Muscle Mass
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,” says Jenaed Brodell, RD, a London-based private practice sports nutritionist.
In reality, evidence suggests that a pound of muscle burns about five calories per day, whereas a pound of fat burns about two calories per day.
During exercise, having more muscle mass will increase your total calorie burn, because your body needs to produce more energy to support the increased rate at which your muscles are contracting.
If you want to enhance your calorie burn, consider stepping up your strength-training game. “Evidence shows that lifting weights burns more fat [than cardio exercise] and has more promising long-term results,” says Brodell, adding the caveat that everyone’s goals and capabilities are different, and ultimately it’s up to you to choose how you exercise.
3. Birth Gender
“Generally, men burn more calories at rest and during exercise than women,” Gonzalez says. But there’s nothing magic about why this is — it’s because men tend to be larger than women, and they have more muscle mass than women of the same age and weight.
“Males generally burn 5 to 10 percent more calories than females at rest, and this percentage usually increases with exercise,” Gonzalez says.
And while women can certainly add muscle mass through strength training, physiological differences mean that, in general, women can’t be as lean as men. “Women are genetically predisposed to lay down more fat to support hormone production and childbearing,” Brodell explains.
The National Institute of General Medical Sciences explains that body fat is also essential for functions such as storing energy, protecting internal organs, and supporting key functions like growth, immunity, hormone production, reproduction, and metabolism.
The American Council on Exercise (ACE) states that men need at least 2 to 5 percent body fat to support health, while women need a minimum of 10 to 13 percent. But these minimum numbers may not be sufficient.
While there’s no official recommendation for optimal body fat percentage, the most cited study on the topic states that a healthy range for adults younger than age 40 is 8 to 20 percent for men and 21 to 33 percent for women. That said, the relationship between health and body fat is complex and not perfectly understood.
“The bottom line is that men and women should focus on building muscle and improving cardiovascular health with a well-balanced cardio and strength-training program,” Gonzalez says.
“After age 30, you begin to lose as much as 3 to 5 percent of your muscle mass per decade.” The reasons for this aren’t perfectly understood, but a review published in July 2017 in Ageing Research Reviews explains that it’s likely because your body becomes more resistant to hormones that promote the protein synthesis that’s key to muscle maintenance. This loss of muscle mass lowers your metabolic rate — the speed at which you burn calories — at rest and during exercise.
A study on human metabolism, published in the August 2021 issue of Science, made headlines for its findings that metabolic rate may not decline throughout adulthood, but rather that it plateaus between the ages of 20 and 60 then begins its decline. In the study, authors measured the energy expenditure of 6,421 men and women between 8 days old and 95 years old using the doubly labeled water technique, the gold standard for this kind of measurement.
Strength training can help you increase your resting metabolic rate, which helps you burn more calories at rest over time.
5. Fitness Level
As your body adapts to training, you will burn less calories with the same workouts.From your lungs to your muscles to your heart to your brain, your body becomes more efficient as you become more fit.
That’s why a newbie might burn significantly more calories than someone who’s been doing the same workout for years — and it’s why changing your workout routine can increase your fitness level and potentially enhance your calorie burn.
6. Training Intensity
It’s also possible that two people doing the same workout are burning a different number of calories because they’re not actually doing the same workout.
Someone exercising at a high intensity, meaning you’re breathing heavily and can’t carry on a conversation, can burn twice as many calories in the same amount of time as someone exercising at a low intensity. And just because you’re covering the same distance as someone else, or going through the same motions, doesn’t mean that the two of you are working out at the same intensity.
While the Department of Health and Human Services (DHHS) explains that walking and running deliver a lot of the same benefits when it comes to lowering blood pressure and reducing your risk of chronic conditions like heart disease and type 2 diabetes, a previous study found that adults who walked one mile burned roughly 89 calories, whereas adults who ran that same mile burned around 113 calories.
Exercise has countless benefits beyond of just burning calories, so the most important thing is to find types of movement that are enjoyable and feel sustainable.
The type of exercise that is better for a person ultimately depends on that person’s goals, physical fitness, and capabilities.