There is a certain amount of calories we each need to eat each day. To work out how many, we use a formula to give your basal metabolic rate (BMR). Basal Metabolic Rate is the mimimal caloric requirement needed to sustain life in a resting individual. This is the amount of energy your body would burn if you slept all day (24 hours).
For you lazy ones who just want to work out your BMR.....skip to the link at the bottom of the page.
Let's look at some factors that affect BMR:
Age: In youth, the BMR is higher; age brings less lean body mass and slows the BMR.
Height: Tall, thin people have higher BMR's.
Growth: Children and pregnant women have higher BMR's.
Body Composition: The more lean tissue, the higher the BMR. The more fat tissue, the lower the BMR.
Fever: Fevers can raise the BMR.
Stress: Stress hormones can raise the BMR.
Environmental Temperature: Both the heat and cold raise the BMR.
Fasting/Starvation: Fasting/starvation hormones lower the BMR.
Malnutrition: Malnutrition lowers the BMR.
Thyroxin: The thyroid hormone thyroxin is a key BMR regulator; the more thyroxin produced, the higher the BMR.
Let's now talk about ways to measure BMR:
1. General Calculation: BMR = your body weight in lbs x 10 kcal/lb
Ex. Joe weighs 150 lbs
BMR = 150 x 10 kcal/lb = 1,500 kcals
2. The Harris-Benedict Equation:
Males: 66 + (13.7 x W) + (5 x H) - (6.8 x A)
Females: 655 + (9.6 x W) + (1.7 x H) - (4.7 x A)
where W = actual weight in kg (weight in lb/2.2 lb/ kg)
H = height in cm (height in inches x 2.54 cm/in)
A = age in years
Ex. Joe weighs 150 lbs, stands 5'6", and is 21 years old
150 lbs/2.2 lb/kg = 68 kg
5'6" = 66 inches x 2.54 cm = 168 cm
BMR = 66 + (13.7 x 68) + (5 x 168) - (6.8 x 21)
BMR = 66 + 932 + 840 - 143 = 1695 kcals per day
NB. for some reason there's a cool face where an 8 should be. Couldn't delete it.
****Just to note, these values are approximations. We can see that we came up with 1,500 and 1,695 kcals per day with two different approaches to figuring out BMR. I would stick to the Harris-Benedict Equation if I were you. I believe it is more accurate!****
Automatic BMR calculator
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http://www.room42.com/nutrition/basal.shtml