Your basal metabolic rate, or BMR,
is the minimum calorific requirement needed to sustain
life in a resting individual. It can be looked at as
being the amount of energy (measured in calories) expended
by the body to remain in bed asleep all day!
BMR can be responsible for burning up to 70% of the
total calories expended, but this figure varies due
to different factors. Calories are burned by bodily
processes such as respiration, the pumping of blood
around the body and maintenance of body temperature.
Obviously the body will burn more calories on top of
those burned due to BMR.
BMR is determined by a combination of genetic and environmental
factors, as follows:
- Genetics : Some people are born
with faster metabolisms; some with slower metabolisms.
- Gender: Because men have a greater
muscle mass and a lower body fat percentage, they
generally have a higher basal metabolic rate.
- Age : BMR is greater in childhood
than in adulthood. After 20 years, it drops about
2 per cent, per decade.
- Weight : The more you weigh the
higher your BMR will be. For example, the metabolic
rate of very overweight women is 25% higher than that
of thin women.
- Height : Tall, thin people have
- Body Surface Area : This is a reflection
of your height and weight. The greater your Body Surface
Area factor, the higher your BMR. Tall, thin people
have higher BMRs. If you compare a tall person with
a short person of equal weight, then if they both
follow a diet calorie-controlled to maintain the weight
of the taller person, the shorter person may gain
up to 15 pounds in a year.
- Body Fat Percentage : Obese People with
a higher body fat percentage, have a lower BMR than
those with a lower body fat percentage - all other
things being equal. Muscle cells contain with tiny
little power centers called mitochondria, which are
where calories get 'burned up.'' The greater percentage
of lean muscle tissue in the male body is one reason
why men generally have a 10-15% faster BMR than women.
- Diet : Starvation or serious abrupt
calorie-reduction can dramatically reduce BMR by up
to 30 percent. Restrictive low-calorie weight loss
diets may cause your BMR to drop as much as 20%.
- Body Temperature/Health : For every
increase of 0.5C in internal temperature of the body,
the BMR increases by about 7 percent. The chemical
reactions in the body actually occur more quickly
at higher temperatures. So a patient with a fever
of 42C (about 4C above normal) would have an increase
of about 50 percent in BMR.
- External temperature : Temperature
outside the body also affects basal metabolic rate.
Exposure to cold temperature causes an increase in
the BMR, so as to create the extra heat needed to
maintain the body's internal temperature. A short
exposure to hot temperature has little effect on the
body's metabolism as it is compensated mainly by increased
heat loss. But prolonged exposure to heat can raise
- Glands: Thyroxin (produced by the
gland) is a key BMR-regulator which speeds up the
metabolic activity of the body. The more thyroxin
produced, the higher the BMR. If too much thyroxin
is produced (a condition known as thyrotoxicosis)
BMR can actually double. If too little thyroxin is
produced (myxoedema) BMR may shrink to 30-40 percent
of normal. Like thyroxin, adrenaline also increases
but to a lesser extent.
- Exercise : Physical exercise not
only influences body weight by burning calories, it
also helps raise your BMR by building extra muscle.
So you burn more calories even when sleeping.
Basal Metabolic Rate (BMR)
BMR is the largest factor in determining overall
metabolic rate and (also) how many calories you need
to maintain, lose or gain weight.
Use the BMR calculator to find out what your BMR figure