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Definition, Calculation, and more...

The basal metabolism represents the calories burned by our body just to stay alive, in the absence of any other activity. Without a doubt, it is the single greatest calorie consumer in our body. Exactly how many calories does it burn? This varies somewhat from individual to individual. (The details are provided further down the page.) Suffice it to say, the basal metabolism burns more calories each day than any physical activity we may engage in.

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In order to keep up its biological functions, our body requires a hefty amount of energy. On average, a person's Basal Metabolism consumes (burns) about 10 calories* per pound of body weight per day.

So, if for instance a person weighs 200 pounds, this person's Basal Metabolism would burn about 2000 calories per day. (This figure may vary somewhat depending on individual factors - see below.) For our purposes, however, the figure of 10 calories per pound per day is a good rough estimate.

Basal Metabolism = 10 x Body Weight (lbs)

Based on the above, a person weighing 200 pounds will need to take in at least 2000 calories per day in order to maintain his or her body weight. This calculation presupposes the respective person is at rest at all times, which in reality of course is not the case.
In reality, the person in question will have a certain level of physical activity each day. More calories will be burned by this activity.

As a rule of thumb:
- Mild physical activity burns about 400-600 calories per day.
- Moderate physical activity burns about 600-1000 calories per day.
- Strenuous physical activity burns in excess of 1000 calories per day.**

These calories need to be added to the Basal Metabolism in order to determine the person's total calorie burn for that day (i.e. the Calorie Output).
So for the sake of our example, if the person is largely sedentary during the day (engaging only in limited walking around the house), the number of additional calories burned would be approximately 400, and the total number of calories burned per day (calorie output) would be 2000 + 400 = 2400 calories per day.

  • As long as that person took in (via food and drink) an amount of calories equal to the one burned by the body (2400 calories a day), his or her body weight would remain unchanged at 200 pounds.
  • If the person took in more calories than the amount burned (say, the person would eat 3000 calories per day), he or she would have an excess of 600 calories per day and would be continually gaining weight. Calories taken in which are not burned by the body are deposited as fat, resulting in net weight gain.
  • If the person took in less calories than the amount burned by the body (say, the person would eat only 1800 calories per day), he or she would have a deficit of 600 calories per day and would be continually loosing weight. The body would have to mobilize fat from its fat deposits in order to fill in the calorie deficit. So in other words, that fat would be burned off, resulting in net weight loss.

Individual Factors affecting the Basal Metabolism:

The following factors decrease the basal metabolic rate, resulting in fewer calories burned at rest:

  • advancing age
  • decreased muscle-to-fat ratio
  • female gender (as compared to male gender), mainly due to the lower muscle-to-fat ratio
  • sedentary lifestyle with physical deconditioning
  • hypothyroidism (a medical condition resulting in low thyroid function)


The following factors increase metabolic rate, resulting in more calories burned at rest:

  • young age
  • regular exercise
  • increased muscle-to-fat ratio
  • male gender
  • active lifestyle
  • pregnancy
  • hyperthyroidism (a medical condition resulting in increased thyroid function)



* Technically speaking, the correct unit of measure is in fact kcal (kilocalories). However, since popular terminology has largely consecrated the term "calories", we will use this term for the purposes of the present document. Please note that in all instances, the term "calories" refers in fact to kcal.

** These numbers are rough estimates and may vary dependent on individual factors.


Return from "Basal Metabolism" to the "Weight Loss Process"








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