Harris-Benedict -Basal metabolic rate Calorie Calc

Harris Benedict equation - Determination of the basal metabolic rate (BMR)

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Background

Basal Metabolic Rate (BMR)
Basal metabolic rate (BMR) is the amount of energy required to maintain the body's normal metabolic activity, such as respiration, maintenance of body temperature (thermogenesis), and digestion. Specifically, it is the amount of energy required at rest with no additional activity. The energy consumed is sufficient only for the functioning of the vital organs such as the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, and skin. 

Variance:
The resting and basal metabolic rate generally decrease with age or if there is a decline in lean body mass. Activities that tend to increase muscle mass (lean tissue) such as body building or strength training (anaerobic activities), will also increase the basal or resting metabolic rate. Aerobic activities such as running, skating, or rope jumping may improve endurance but have little effect on the basal or resting metabolic rate (see post-exercise expenditure below). Other factors that may affect the BMR or RMR include stress, illness, hormone levels (e.g. thyroid), environmental (e.g. temperature or altitude) or any other factor that effects the normal functioning of one or more vital organs.

Lean tissue requires significantly more energy to maintain because of the increased level of metabolic activity. In contrast, fat tissue requires very little energy to maintain and has little influence on the resting or basal metabolic energy needs.

Greater lean body mass = Greater BMR or RMR.

Because individuals can increase their total lean body mass through strength training (corresponding increase in skeletal muscle), it is possible to increase the overall basal energy requirements at rest.

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Age:      Gender: Male Female

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Height:  Inches Centimeters 

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Weight:  Kilograms Pounds

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The  activity level below will be used along with the BMR to calculate a
rough estimate of the number of  calories needed per day (kcal/day)

Current daily activity level?

[Sedentary] [Mild activity] [Moderate activity] [Heavy activity] [Very Heavy - Extreme]

 

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Background

Harris Benedict Equations:

BMR calculation for men (metric)
BMR = 66.47 + ( 13.75 x weight in kg ) + ( 5.003 x height in cm ) - ( 6.755 x age in years )


BMR calculation for women (metric)
BMR = 655.1 + ( 9.563 x weight in kg ) + ( 1.850 x height in cm ) - ( 4.676 x age in years )


Post-exercise energy expenditure: the amount of additional energy (above the resting or basal metabolic needs) expended after an activity depends on the intensity and duration of the exercise session. More intense sessions tend to increase resting energy needs for longer time periods. These increased energy requirements occur during the cool-down phase and are short-lived. Sustained increases in the resting or basal metabolic rate can only be obtained through regular strength training routines that increase lean body mass.

Summary:
Aerobic activity: short lived increases in RMR/BMR (cool-down period)
Anaerobic activity (regular): increases in lean body weight (LBW) --> Sustained increases in RMR/BMR.

Utilization

Utilization: The baseline BMR or RMR can be used along with stress/activity factors to estimate the daily caloric needs of an individual - (Total Energy Expenditure (TEE)  (kcal/day)).   See error rate below.

Total Energy Expenditure (TEE)
The total energy expenditure (amount of calories needed per day) is composed of three primary factors: (1) Resting or basal metabolic rate   (2) Thermic effect of food  (3) Activities of daily living (ADL) - physical activity.

Thermic effect of food (TEF):
Rough estimation: TEF = Total calories consumed/day x 0.1
   Example: 2000 kcal diet.    TEF = 2000 x 0.1 = 200 kcal/day.

TEF of protein >>carbohydrates>>fats.

Graphical representation:

Measurement versus predictive equations:

Direct measurement:  Method: direct or indirect calorimetry.
BMR:   Conditions: measured under very restrictive circumstances  and strict adherence to  protocols. This method is generally impractical in most cases. 
RMR:  less restrictive conditions and more easily obtained.  The resting metabolic rate is only marginally different from the BMR.

Predictive equations:
An alternative method is to use predictive equations that can provide a rough estimate of the basal or resting metabolic rate.  The basal or the resting metabolism is the largest component of the total energy expenditure (TEE).... usually 60 - 75%.  The RMR or BMR is usually at the higher end of this range for sedentary individuals (70-75%) and at lower the end for athletes. 

Error rate of predictive equations:

The various predictive equations for determining the resting or basal metabolic rates may significantly under or overestimate the total calories needed to maintain the current weight of an individual when combined with stress/activity factors that are selected by the user. This variance can approach 20% (over or underestimation) depending on differences in  body composition (lean versus obese),  actual activity levels (athletic versus sedentary lifestyle), and energy levels expended in thermogenesis.


 

Activity / Stress factors:

The following activity/stress factors when used along with an estimation of the resting or basal metabolic rate can be used to estimate an individual's total energy expenditure (TEE) in kcal/day  (recommend daily calories to maintain current weight = RMR + TEF + ADL).

Sedentary.  Little to no exercise	Daily calories needed = BMR x 1.2
Mild activity level: Intensive exercise for at least 20 minutes 1 to 3 times per week. This may include such things as bicycling, jogging, basketball, swimming, skating, etc.  If you do not exercise regularly, but you maintain a busy life style that requires you to walk frequently for long periods, you meet the requirements of this level.	Daily calories needed = BMR x 1.3 - 1.375
Moderate activity level: Intensive exercise for at least 30 to 60 minutes 3 to 4 times per week. Any of the activities listed above will qualify.	Daily calories needed = BMR x 1.5 - 1.55
Heavy or (Labor-intensive) activity level: Intensive exercise for 60 minutes or greater 5 to 7 days per week (see sample activities above).  Labor-intensive occupations also qualify for this level.  Labor-intensive occupations include construction work (brick laying, carpentry, general labor, etc.). Also farming, landscape worker or similar occupations.	Daily calories needed = BMR x 1.7
Extreme level: Exceedingly active and/or very demanding activities:  Examples include:  athlete with an almost unstoppable training schedule with multiple training sessions throughout the day or a very demanding job, such as shoveling coal or working long hours on an assembly line. Generally, this level of activity is very difficult to achieve.	Daily calories needed = BMR x 1.9

Reference

Harris JA, Benedict FG. A biometric study of human basal metabolism. Proc Natl Acad Sci USA 1918;4(12):370-3.