Your body doesn't just burn calories when you are physically active. It burns calories for basic physiological processes such as digestion, heart rate and blood circulation, hormonal activity, cellular metabolism, body temperature control and respiration. The number of calories you burn each day depends on your height, body weight and basal metabolic rate. Once your body burns calories to get the energy it needs for life-sustaining functions such as breathing, the calories you burn through physical activity are extra.
Number of Calories You Burn
Your basal metabolic rate -- the minimum number of calories your body needs each day to carry out its basic functions -- accounts for up to 70 percent of the total number of calories you burn each day, according to the Mayo Clinic. Even when your body is at rest, it needs a certain number of calories to provide the energy for breathing and maintaining other life functions. Daily calorie requirements vary among individuals depending on their activity level, muscle to fat ratio and differences in inherited metabolic rate. Some people have a low BMR, and therefore; they burn fewer calories while at rest or sleeping.
Basal Metabolic Rate
Several factors influence your basal metabolic rate. Your gender, age and body size and composition all play a role, says the Mayo Clinic. Men usually burn more calories than women the same age because they generally have less body fat and more lean muscle mass. Muscle needs more energy than fat does so you burn more calories. As a result, larger individuals and those with more muscle burn more calories even when the body is at rest. The amount of muscle in your body also decreases with age. As fat accounts for a higher percent of your body weight, your metabolism slows more.
Estimating BMR
Employees at Parkland Health Center in Farmington, Missouri, recommend multiplying your body weight in pounds by 10 for women and by 11 for men to quickly calculate your BMR. This will give you a close estimate of the number of calories you need to consume each day. A more accurate way to calculate your BMR also takes into account your gender and age. The Harris-Benedict principle uses different formulas for each sex. BMR for women is based on the formula 655 + (4.3 x weight in pounds) + (4.7 x height in inches) -- (4.7 x age in years). Men need to use the formula 66 + (6.3 x weight in pounds) + (12.9 x height in inches) -- (6.8 x age in years) to calculate BMR.
Level of Physical Activity
Regular physical activity burns the most calories and is necessary if you are trying to maintain or lose weight. Improving your basal metabolic rate can also help your body burn calories more efficiently, according to the Cleveland Clinic. Because the amount of your physical activity can affect your BMR, you should calculate the number of calories you expend for daily physical activity. If you perform daily chores and are somewhat active, multiply your BMR by 37.5 percent. Being moderately active means that you are frequently on the move and exercise on most days of the week. In this case, you should multiply your BMR by 40 percent. Athletes and very active individuals who exercise vigorously every day should use the 50 percent factor. Multiplying your BMR by these percentages will give you the number of calories you burn each day performing physical activities.
References
- Mayo Clinic; Metabolism and Weight Loss -- How Your Burn Calories; Mayo Clinic Staff; October 2009
- Canada; How Many Calories Do You Really Need; MediResource Clinical Team
- ShapeFit; Basal Metabolic Rate -- Learn How To Calculate and Find Your BMR; 2011
- Parkland Health Center: Calorie Needs -- Calculate Your Basal Metabolic Rate
- Weill Medical College of Cornell University; Basal Energy Expenditure -- Harris-Benedict Equation; October 2000
- Cleveland Clinic; Strength Training; 2011
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