How Many Calories Does the Body Naturally Burn Per Day?

It's disheartening when you sprint as fast as you can on the treadmill gasping for air and look down to see that you've only burned 100 calories. The amount of work it takes to burn only a few hundred calories is intimidating, but you shouldn't get too invested in that number. Throughout the day your body burns hundreds or thousands of calories whether you exercise or not.

Just to stay alive your body is constantly at work building, repairing and regulating cells. Even when you sleep, you're burning calories constantly. The number of calories your body burns taking care of itself is usually higher than the number of calories you burn from working out.

Resting metabolic rate, which is similar to basal metabolic rate, is the number of calories you burn at rest. It's the amount of energy you use every day for your body to function normally. Throughout the day, your heart needs energy to beat, your brain needs energy to power nerves, your digestive system needs energy to digest and so on.

To figure out your average calories burned per day, start by using equations or lab testing to find your resting metabolism. There are online calculators that can give you a rough estimate based on age, height, weight, gender and activity level. Currently a couple of equations are used, and one is more accurate than the other.

The Harris-Benedict Equation has been used for over 100 years to find a rough estimate of metabolism. It uses height, weight, age, gender and activity level to figure out your resting metabolism. Similar to Harris-Benedict, the Mifflin St. Jeor equation uses the same factors but is more accurate.

These equations are found in many online calorie calculator websites. Unfortunately they're not as accurate as lab equipment, which takes much of the guesswork out of the process. There are a few different ways to measure your metabolism in a lab.

Indirect calorimetry is precise and relies on gas exchange, rather than any precise measurements of your body. In the lab you lie on a table and a large helmet is placed on your head. It seals your head from air, except for a tube which is attached to the helmet.

Through this tube you can draw air in and push it out of the helmet. The tube is hooked up to a metabolic cart, which has a computer that measures the amount of oxygen and carbon dioxide that go in and out of the helmet.

To accurately complete the test, you also have to submit a urine test to see how much nitrogen you excrete, which determines that amount of protein your body metabolizes. All this information is run through something called the Weir equation, which calculates your resting metabolic rate.

The most accurate way to measure your metabolism is to figure out how much metabolically active tissue you have in your body. Muscle cells, organ cells, blood cells and immune cells are all metabolically active.

You can figure out roughly how much of this active tissue you have in your body using a DEXA scan, which is one of the most accurate measuring tools available. DEXA scans show you how much body fat, muscle and bone tissue is in your body. They're also used for bone density scans to figure out if you're suffering from osteoporosis.

Unfortunately, lab testing can be expensive and time-consuming, so you might have to stick to using online calculators to figure out your resting metabolic rate. Whatever method you use to figure out your daily caloric expenditure, it's important to understand that this number can change throughout your life.

The biggest factor in your metabolism is the amount of muscle mass you have, according to a 2016 study published in Current Biology. Muscle is incredibly active tissue. It's a massive source of protein for your body. If another area needs protein, your body can break down muscle and send it to that area.

Muscles also help regulate hormones, bone health and inflammation. Muscle uses both fat and glucose as fuel, which helps control the amount of fat and sugar in your blood. Muscle mass makes you more sensitive to insulin, which could help someone suffering from type 2 diabetes.

The more muscle you build, the higher your metabolism climbs. A 2014 study published in the European Journal of Clinical Nutrition found it's hard to determine your metabolism when you use a calculator and not a machine because the calculators can't figure out how much muscle mass you have.

When you work out your body naturally burns calories, but the calorie burn doesn't always stop when the workout ends. Depending on the type of workout you're doing, your metabolism can remain elevated for hours after activity. This phenomenon is termed excess post-exercise oxygen consumption, or EPOC.

EPOC is measured in a similar way to indirect calorimetry, where you analyze the amount of oxygen and carbon dioxide going into and leaving the body. By measuring these numbers before and after exercise you can figure out the different between oxygen consumption before and after exercise.

Certain types of exercise boost your metabolism more than others. Intense resistance training or high-intensity interval training raise your EPOC more than slower endurance exercise, according to a 2015 study published in Research Quarterly for Exercise and Sport.

Read more: One Simple Change That Will Maximize Fat Loss

Your resting metabolism burns the majority of calories per day, around 60 percent for sedentary individuals according to an article from UC Denver. On top of that, you can work out to burn more. Activity can be broken down into exercise and daily tasks like walking and cleaning.

Read more: How to Raise Your Basal Metabolic Rate

Your metabolism can change to burn more calories but it takes time. So what's the fastest way to burn calories? Exercise! The number of calories you burn during your workout depends on the exercise you do and factors like body weight. Heavier people burn more calories, even if they do the same exercise.

Height, weight and gender help determine how many calories you burn from a workout. According to the United States Department of Agriculture, a 5 foot, 10 inch tall 154-pound man will burn 280 calories from walking at 3.5 miles per hour for one hour. The same man would burn about 590 calories from an hour of biking.

Non-exercise activity thermogensis is the number of calories that you burn from activities like cleaning that don't count as a workout. It could even be walking up and down a flight of stairs. Since it can be sporadic, this number is difficult to accurately measure.

On top of metabolism and exercise, digesting food can naturally raise your daily caloric expenditure. An estimated 5 to 10 percent of the calories you burn are from digesting and storing food, according to the Mayo Clinic.

It takes energy to heat, churn and move the food you eat. Then you have to break it down and store the nutrients throughout your body. As you can see, the number of calories burned on the treadmill is just the tip of the iceberg.