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 By Elena Voropay
Trying to determine your caloric need for the day? What is involved in the equasion? Remember that resting metabolic rate is the largest contributor to total energy expenditure, accounting for approximately 60% to 75% of daily energy expenditure. It is a measure of the calories required for maintaining normal body functions such as heart beat, breathing, thinking, and even regulating body temperature. You can increase your resting metabolic rate by adding lean tissue (or building muscle) and by engaging in physical activity. However, there are other factors that influence your energy expenditure. Hyperthyroidism, menstrual cycle, younger age, and increased body temperature all increase your resting or basal metabolic rate. On the other end, low caloric intake, hypothyroidism and loss of lean tissue contribute to slower metabolism.
Calculate Your BMR
There are several formulas used to assess the BMR. These formulas will help you determine how much energy you need to maintain the functionality of your body when at complete rest. In other words, BMR in calories shows the amount of food you need to eat in 24-hour period just to keep yourself alive. Note, that 1kcal = 1000 cal, but for ease of use contemporary literature utilizes a simplified version of measure in calories, even though it is inaccurate and should be stressed that the actual numbers are kilocalories (or the above estimated BMR would be 2,137,000 cal/day).
1. The most basic formula for knowing how many calories you burn at rest, but it does not take into consideration such factors as lean mass, sex, age, height.
BMR = your body-weight (in pounds) x 12
Example:
For a 200-pound male BMR = 200 x 12 = 2,400 kcal/day
1.If you want to take advantage of your gender, this formula is quite useful.
BMR = gender factor (1.0 kcal/kg/hr for men; 0.9 kcal/kg/hr for women) x weight in kilograms (1kg = 2.2 lb.) x 24 hours
Example:
a) Convert body-weight in pounds to kilograms by dividing by 2.2: 200 pounds / 2.2 pounds per kilogram = 90.9 kg
b) Multiply weight in kilograms by the BMR factor: 90.9 kg x 1 kcal/kg/hr = 90.9 calories per hour
c) Multiply the calories used in one hour by the hours in a day: BMR = 90.9 kcal x 24 hrs = 2,182 kcal/day
2.Harris-Benedict equation provides two formulas for different genders: Men BMR = 66 + 13.8(weight in kg) + 5 (height in cm) - 6.8 (age)
Example:
200-pound (90.9 kg) male who is 30 years old and 6 foot tall:
a) Calculate height in foot to inches: 6 x 12 = 72 inches
b) Convert inches to centimeters (one inch = 2.5 cm) : 72" x 2.5 cm = 180 cm
c) BMR = 66 + 13.8 x 90.9kg + 5 x 180cm - 6.8 x 30yrs = 66 + 1254 + 900 - 204 = 2016 kcal/day
Women BMR = 655 + 9.6 (weight in kg) + 1.8 (height in cm) - 4.7 (age)
Example:
120-pound female who is 30 years old and 5 foot 5 inches tall:
a) Convert body-weight in pounds to kilograms by dividing by 2.2: 120 lb./ 2.2 = 54.5 kg
b) Calculate height in inches: 5 foot x 12 + 5 = 65 inches
c) Convert height in inches to centimeters: 65" x 2.5 cm = 162.5 cm
d) BMR = 655 + 9.6 x 54.5kg + 1.8 x 162.5cm - 4.7 x 30yrs = 655 + 523.2 + 292.5 - 141 = 1,330 kcal/day
3.If you know your body composition, the exact proportion of fat-free mass (muscle/lean tissue) to your adipose, the following equation can be used to predict BMR.
BMR = 370 + 21.6 x fat-free mass in kg
Example:
A 200-pound male who has 10% body-fat
a) Calculate total fat in pounds: 200lb x 10% = 20 lb. of fat
b) Assess the amount of lean tissue: 200lb - 20 = 180 lb.
c) Convert muscle mass in pounds to kilograms: 180lb / 2.2 = 81.8 kg
d) BMR = 370 + 21.6 x 81.8kg = 2,137 kcal
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