Most people are fond of referring to either having a slow or a fast metabolism. This inference is often made to explain why some people find it very easy putting on weight but difficult losing the weight. While the fact remains that metabolism does affect a person’s ability to lose weight, there is more to it than meets the eye.
Metabolism is the rate at which your body burns calories by means of continuously running chemical processes inside your body in order for it to stay alive and to function normally. In simpler terms, metabolism can also be referred to as the process through which your body converts food into either energy or fat.
Those with a fast metabolic rate will burn calories faster so that there is no storage of excess fat in the body whereas those who have a slow or poor metabolic rate will burn calories a lot of slower and thus causing the body to store the extra calories as fat in the body.
The most important factor in determining overall metabolic rate and thus how much calories is required to maintain, lose or gain weight is what is referred to as the “resting metabolic rate” RMR or “basal metabolic rate” BMR. It is the energy required by the body to maintain vital bodily functions such as heart rate, body temperature, brain function, blood pressure, and respiration while the body is at rest.
Thus the Basal Metabolic Rate (BMR) refers to the energy your body needs to maintain itself and this accounts for about 50-80 per cent of your total energy usage which automatically makes it the biggest contributor to your overall metabolic rate.
However, there are several interdependent factors – all working in combination – that influence your BMR. While we can influence some of these factors mostly involving physical activities, there are those we simply cannot control. Here is a list of some of these factors in no particular order.
Like they say, itâ€™s all in the genes. Differences in our genetic predispositions make some people to naturally have a faster metabolism, while others have a naturally slow metabolism. While you cannot change genetics, you can still win the battle against excess weight gain.
There are certain glands in the body especially the thyroid and adrenal glands that play major roles in regulating the body’s BMR. Adrenalin produced by the adrenal glands increases BMR, however to a lesser degree. The thyroid gland produces a chemical called thyroxin which generally speeds up the metabolic activities of the body.
Hypothyroidism (inability of the thyroid gland to produce enough thyroxin) slows down metabolism and usually leads to weight gain, lethargy, constipation and depression. On the other hand, hyperthyroidism – overactive thyroid – releases greater amount of thyroxin than necessary and generally speeds up metabolism and causes weight loss, increased appetite and often nervousness.
On an average, men have a BMR of about 7,100KJ per day while women have about 5,900KJ per day. This is mostly due to the effect of male sex hormones which men to have a greater muscle mass and lower body fat percentage as compared to women. This means that men require a higher metabolism to main their muscles thus increasing their basal metabolic rate.
After the age of 30 (some experts argue at 25), there is a decrease in the metabolic rate of both men and women due to a loss in muscle tissue coupled with both hormonal and neurological changes. However, regular exercise in adulthood can help in slowing this process and increasing metabolism.
BMR increases with weight and therefore heavier people need a lot more calories to maintain their body weights.
This has to do with your height and weight ratios. The higher your total body surface area is, the more body cells there are to maintain requiring more calories, thus leading to a higher BMR.
Body Fat Percentage
Fat cells are generally sluggish and burn far fewer calories than other body tissues and organs. Therefore your body composition – difference between total lean weight and fat weight – goes a long way to determine the speed of your metabolism.
Lean body weight is more metabolically active at rest thus individuals with a higher percentage of lean body weight have a higher basal metabolic rate when compared with individuals of the same weight who have a higher body fat percentage.
Super low calorie diets, eating disorders or starvation can cause the body to enter into “starvation mode” which essentially slows down your metabolism to keep your body from burning too much calories.
Internal and external temperatures that affect the body’s temperature have an effect on BMR as the body keeps trying to maintain a constant body temperature. When the body feels cold, it will need to burn up more calories to produce heat to keep warm. When it feels too hot, the body also burns more calories through the process of sweating.
Certain drugs like nicotine and caffeine are known to influence the speed of metabolism. However the increase is temporary and the risks generally outweigh the benefits.
Regular physical exercise helps in burning calories while exercising and also in building extra lean tissue which is more metabolically active while you are resting than fat tissue.