Basal Metabolic Rate - BMR
BMR is the largest factor in determining overall metabolic rate and 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 slower metabolisms.
* Gender. Men have a greater muscle mass and a lower body fat percentage. This means they have a higher basal metabolic rate.
* Age. BMR reduces with age. After 20 years, it drops about 2 per cent, per decade.
* Weight. The heavier your weight, the higher your BMR. Example: the metabolic rate of obese women is 25 percent higher than the metabolic rate of thin women.
* 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. The lower your body fat percentage, the higher your BMR. The lower body fat percentage 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 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 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 the BMR 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 lean tissue. (Lean tissue is more metabolically demanding than fat tissue.) So you burn more calories even when sleeping.
When we burn fat, or other nutrients, heat is produced, which is measured in calories. As you note, each gram of fat generates 9 calories, and 454 grams equals one pound. But a pound of fat is not all fat. It's about 10% water. All of our body tissues--fat, muscle, bone, skin--contain some water. And water has zero calories.
Two other minor points: The calories can be reduced when the meal is high in fiber. Fiber speeds the movement of food through the digestive system, there is less time for the nutrients to be absorbed before they are eliminated. So the non-absorbed fat could be a bit higher. Also, the amount of heat generated from fat differs a little for various foods (depending on fatty acid content). For example, there are 9.50 calories in one gram of meat compared with 9.30 calories for vegetables and fruits and 9.25 calories for dairy products.
* So to lose one kilogram of fat per fortnight, it is necessary to either reduce our food intake by approximately 7000 calories (29,400 kilojoules) or to exercise so that 7000 calories (29,400 kilojoules) are burned.
Seeing that fasting for the required 4 days would greatly deteriorate our health, we have no option other than to exercise if we wish to lose weight.
Any movement is considered exercise, so let's all get up and start burning off some of those heavy fat rolls.