What is Basal Metabolic Rate (BMR)?
BMR is the largest factor in determining the overall metabolic rate and also how many calories you need to maintain, lose or gain weight. BMR is determined by a combination of genetic and environmental factors, as follows:
Genetics: Some people are born with faster metabolisms; some with a slower metabolism.
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 percent, per decade.
Weight: The more you weigh the higher your BMR will be. For example, the metaboli rate of a very overweight woman is 25% higher than that of a thin woman.
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.
Body fat percentages: People with a body fat percentage have a lower BMR than those with a lower body fat percentages- all other things being equal. Muscle cells contain tiny little power centers called mitochindira, 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 srupt 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 temperature. 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 compensatedmainly by increased heat loss. But prolonged exposure to heat can raise BMR.
Glands: Thyroxin (produced by the thyroid 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 muchthyroxin 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 the BMR but to a lesser extent.
Exercise: Exercise not only influences body weight by burning calories, but it also helps raise your BMR by building extra muscle. So you burn more calories even when sleeping.