May 26, 2009
1) Basal Metabolic Rate (BMR)
BMR is the total number of calories your body burns for normal bodily functions,
including digestion, circulation, respiration, temperature regulation, cell construction, and
every other metabolic process in your body.
In other words, your BMR is the sum total of all the energy used for basic bodily functions, not including physical activity.
BMR usually accounts for the largest amount of your daily calorie expenditure – about two thirds. BMR is at its lowest when you’re sleeping and you’re not digesting anything.
BMR can vary dramatically from person to person depending on genetic factors.
You probably know someone who can eat anything they want yet they never gain an ounce of fat. This type of “fast metabolism” person has inherited a naturally high BMR.
2) Activity Level
Next to BMR, your activity level is the second most important factor in how many
calories you need every day.
The more active you are, the more calories you burn; it’s that simple.
Become more active and you burn more calories. Sit on the couch all day long and you hardly burn any.
Your total body weight and total body size are also major factors in the number of
calories you require.
The bigger you are, the more calories you’ll require to move your
4) Lean Body Mass (LBM)
Total body weight correlates with the number of calories you require, but separating your
total weight into its lean and fat components allows you to calculate your calorie needs
even more accurately.
The higher your LBM, the higher your BMR will be.
This is very significant when you want to lose body fat because it means the more muscle you have, the more calories you will burn at rest.
Muscle is metabolically active tissue, and it requires a great deal of energy to sustain it.
The best way to increase your BMR is to increase your LBM. This is why you could say that weight training helps you lose body fat, albeit indirectly.
Metabolic rate tends to slow down with age.
Therefore, the number of calories the average person requires also goes down with age.
Fortunately, you can prevent and even reverse the age-related slowdown in metabolism by developing more muscle through weight training and nutrition.
Men usually require more calories than women.
The average male has a maintenance level of 2800 calories per day. The average female requires only 2000 calories per day to maintain.
The reason for this difference is not so much a sex-related issue as a body
weight and muscle mass issue;
the average man carries much more muscle mass than the average female and this explains the spread in calorie requirements between men and women.
Except for individual genetically-related differences in BMR, a 140 pound man and a 140 pound woman would have the same calorie requirements if their activity levels were identical.