What Is a Calorie?
A calorie is simply a unit of heat energy. It's defined as the amount of heat needed to raise the temperature of 1 gram of water 1 degree C. In terms of nutrition, a calorie is a measure of how much energy the body needs to function. Some foods have more potential energy than others.
In the U.S., the words "kilocalories" and "calories" are used interchangeably when talking about diet and exercise. Technically, a kilocalorie (or Calorie) is 1,000 calories, but since a calorie is too small a measurement for nutrition purposes, the kilocalorie is used, but its name is shortened to "calorie."
Think of calories as fuel for your body. Like a car, your body needs to burn fuel to work. Your body's calorie needs are like the gas tank in your car. If you let the tank get empty, your car won't drive. If you don't give your body enough energy, it can't work properly.
A big difference, though, is that your car's gas tank has limited room for fuel. You can't overfill it. But you can easily put more calories in your body than you need on a given day. When that happens, the excess energy is stored in fat cells so that you can use it later. Doing that too often leads to weight gain.
What Is Metabolism?
When your body processes food into energy, it's called metabolizing. Your metabolism is the system for turning food into energy that you can use to keep your body working. Your body uses energy all the time, even when you're asleep. You are constantly metabolizing calories. The energy is used to fuel the functions in your body.
Here are some key things to know about the process:
Basal metabolic rate. This is the number of calories you need to keep all your basic bodily functions going. This includes breathing, your heartbeat, your nervous system, and all the rest of the automatic things your body does every day.
Thermogenesis. This is a technical term for the energy it takes to convert food into usable energy. Eating, digesting, transporting, and storing food inside your body takes up to 10% of the energy from the food you eat.
Physical activity. Moving your body demands more energy. This is in addition to what you're using to keep all the essential functions going. Every action, no matter how large or small, takes some number of calories. A simple task like unloading a dishwasher uses a small number of calories. Strenuous activities use more calories.
How Many Calories Am I Using?
Every person is slightly different. There are calculators that will tell you your non-exercise calorie needs based on your age, weight, and sex.
For example, a moderately active 50-year-old man who’s 5'10" tall and weighs 165 pounds needs 2,400 calories per day to maintain his weight. A moderately active 50-year-old woman who’s 5'6" and 135 pounds needs 1,900 calories per day to maintain her weight. Younger people tend to burn more calories than older people.
Exercise burns more. Adding physical activity to your day ups the number of calories your body burns. Different kinds of exercise take different amounts of energy. A 160-pound person doing 1 hour of exercise might use up the following number of calories for these activities:
- Elliptical machine: 365 calories
- Golf (carrying clubs): 314 calories
- Running (5 mph): 606 calories
- Walking (3.5 mph): 314 calories
- Bicycling (under 10 mph): 292 calories
- Hiking: 435 calories
The most effective way to burn more calories is by adding physical activity into your routine. Your basal metabolic rate remains reasonably steady, though it does get slower as you age. Researchers have found that you can speed it up a little bit by building more muscle. That’s because muscle requires more energy than fat. More muscle tissue means you burn more calories overall.
Health condition effects. Some health problems lower basal metabolic rate, such as thyroid disorder, polycystic ovarian syndrome, or Cushing's syndrome. These are not very common, though. If you’re concerned that you might have any of these issues, you can ask your doctor to do tests to find out what’s going on with you.
Most experts suggest that 30 minutes a day of activity is good for overall health and for burning extra calories. Talk to your doctor if you have questions about adding exercise into your daily routine -- they can help you get started.
Average calories burned per day
This is based on your basal metabolic rate (BMR), which varies depending on your age, sex, height, weight, and genes. Remember that BMR is just the energy you spend to keep your body going and doesn't take exercise into account. The BMR is calculated in several different ways, and you may get different results depending on which calculator you use.
Here are some examples of BMRs, using the "average" man and woman as determined by the CDC. For comparison, we've included how many calories this average man and woman would burn if they're moderately active (meaning, they do moderate exercise for 30 minutes most days of the week).
Calories Burned Daily
| Age | BMR Man | Moderately Active Man | BMR Woman | Moderately Active Woman |
| 20 | 2,450 | 2,950 | 1,950 | 2,300 |
| 30 | 2,400 | 2,850 | 1,850 | 2,250 |
| 40 | 2,300 | 2,750 | 1,800 | 2,200 |
| 50 | 2,250 | 2,650 | 1,750 | 2,100 |
| 60 | 2,150 | 2,600 | 1,700 | 2,050 |
| 70 | 2,050 | 2,500 | 1,650 | 2,000 |
Figures based on an "average" man and woman in America, according to the CDC. The average man is 69 inches tall (5 feet 9 inches) and weighs 200 pounds. The average woman is 63.5 inches (5 feet 3.5 inches) and weighs 171 pounds.
Takeaways
The number of calories you burn in a day depends on your age, sex, weight, and how much physical activity you do. A sedentary person burns less calories each day than someone exercising. Several daily calorie burn calculators are available on the internet to help you find out how many calories you burn each day.
Burning Calories FAQs
How many calories do you naturally burn in a day?
That depends on your age, sex, height, and weight. It can approximately range from 2,000 to 2,450 calories for men and 1,600-1,950 for women (not including calories burned from exercise).
How many calories does 10,000 steps burn?
That also depends -- on your weight, exercise intensity (are you walking or running?) and how long it took you to do those 10,000 steps (30 minutes or 60?). One study showed that calories burned for 10,000 steps ranged from about 150 to 900, depending on how fast participants walked and how long it took them to do the steps.
