Understanding your personal caloric needs and the effect of physical activity on those needs is important, it can also be unnecessarily confusing. Basically, the number of calories you need to eat each day is derived from many factors including your age, weight, height, gender, lifestyle, and overall health and fitness. It is common sense that a physically active 6 feet tall, 20 year-old man or woman needs more calories than a less active, 5-foot, 75 year-old man or woman ... but how does a person find out how many calories they need based on their lifestyle and metabolism? It's really not that hard.
You've probably heard of BMR or basal metabolic rate. Your basal metabolic rate is the minimum number of calories you would need to perform all bodily functions while sleeping for an entire day. Those functions include keeping the heart beating, respiration, digestion, creation of new blood cells, temperature maintenance and metabolic processes. It does not include physical activities, still these basic functions can require as much as 70 percent of the total calories burned in a single day for some individuals. The first step for any individual who has a fitness goal to lose, maintain or gain weight is to determine the total number of calories that their body uses for basic functioning - their BMR- and daily activities per day.
A common method for measuring daily calorie usage is the Harris-Benedict equation. It estimates your basal metabolic rate, which is then multiplied by your level of activity. The result is your recommended daily calorie intake.
The method is simple. First calculate your basal metabolism rate using the formula below
For adult women: 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years ) = BMR
For adult men: 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year ) =BMR
As an example, if you are a 25 year-old adult woman who weighs 130 pounds, is 5'4" tall, and your fitness regimen includes moderate exercise three to five days per week, the steps to calcluate your BMR and calorie requirement calculations would be:
First, use your weight, height and age to find the basal metabolic rate.
655 + (4.35 x 130) + (4.7 x 64) - (6.8 x 25)
or 655 + 565.6 +300.8- 150 =1371.4
Then calculate your estimated daily caloric requirements by multiplying the basal metabolic rate (in this example, 1,371.4) by the appropriate physical activity item in the list below.
- Sedentary lifestyle: little or no physical activity - BMR x 1.2
- Slightly active lifestyle: light exercise between once and three times per week - BMR x 1.375
- Moderately active lifestyle: moderate exercise three to five days per week - BMR x 1.55
- Active lifestyle: intense exercise six to seven times per week - BMR x 1.725
- Very active lifestyle: heavy/intense exercise twice a day - BMR x 1.9
Using this method, a 25 year-old adult woman who weighs 130 pounds and is 5'4" tall who maintains a moderate exercise regimen three to five days per week has an estimated basic calorie requirements of 1646.1 x 1.55 or 2,126 calories per day
Unfortunately, the Harris Benedict equation does not take body mass or density into consideration, so remember, muscle burns more energy than fat, so you may need to tweak your intake needs.
This is a great tool to help you design your fitness and nutrition needs throughout our adult life!
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