What Is Metabolism?

Metabolism is a chemical process that occurs in our body in order to maintain our life. Scientifically speaking, there are two kinds of metabolism: constructive metabolism and destructive metabolism. The former is the synthesis of the proteins, carbohydrates, and fats that form tissues and store energy (as body fat) and the latter is the breakdown of complex substances and the consequent production of energy and waste matter. However, in a context of weight loss/gain, we can think about metabolism as the efficiency of energy used by our body. The faster the metabolism, the higher the usage of stored energy (e.g., body fat, carbohydrate in our blood stream and in the cells), and consequently the faster you can lose weight.

Why metabolism is so important in weight loss? It is because weight loss/gain does not happen overnight. It is a gradual process. A tiny bit of excess or deficiency of calories make a big difference in the long run. If you can boost your metabolism just a little bit, by, say, 100 calories a day, without changing anything else, you can lose almost 10 pounds of body weight in a year.

There are several factors that are related to the usage of the calories: Resting Metabolic Rate, Thermic Effect of Food, Physical Activities, and Temperature of the Environment. When we talk about Metabolism, most people think of Resting Metabolic Rate. In fact, this is the most important one; so let’s start with the Resting Metabolic Rate.

A woman sleeping

Even if you are sleeping all day long, you are using some calories to maintain your body functions.

Resting Metabolic Rate (RMR)

RMR is the minimum amount of energy you need to keep your body running. Even if you are lying on the bed all day long, you still use up this much energy. About 75 to 80% of energy is used to maintain the function of vital organs, such as the brain and the heart. Just keeping the muscles warm, the body spends about 20% of the energy, and it even spends about 5% of energy to keep the body fat as it is. For a 130 pound woman, RMR is around 1,300 calories a day. If your RMR is lowered by 100 calories because of a loss of muscles, you may gain about 10 pounds of the body fat in one year. Therefore, it is important to keep RMR high.

If you like to know your resting metabolic rate, please go to BMI for Women page. The BMI calculator on the page also provides an estimate of your resting metabolic rate.

Thermic Effect of Food (TEF)

When we eat, not all calories from the food go to the body. Some of them are used for digesting that food. In fact about 10% of energy expenditure of the day goes to the digestion. In some cases, digesting food requires more calories than the calories that you get from the food (celery is a good example). It takes about 27 calories to digest 100 calories of protein, 23 calories to digest 100 calories of carbohydrates. Unfortunately most popular “food” in the US is fat and it takes only 3 calories to digest 100 calories of fat. Further, one gram of protein and carbohydrate gives you only 4 calories, but fat gives you 9 calories. No wonder people gain weight! Replacing fat with protein or carbohydrate increases energy usage of digestion, and it is a good thing to do.

Physical Activity

We all know that we need to exercise, but there is more about physical activity. Some people complain that they go to the gym 3 times a week but still gain weight. If you look closer to their daily activities, however, you can tell why. They go to the gym, take 5 minutes to change clothes, another 10 minutes to chat with friends, 15 minutes on a tread mill, and that’s all. When they get out of the gym, they hop in the car, drive home, and the rest of the day, they sit in front of the computer or TV.

You need to think small. Every small activity counts. Taking a flight of stairs several times a day in the office, or getting off one bus stop earlier and walking to the office, or even fidgeting in the chair all day long make a BIG different in a long run. For example, one study fed people 1,000 calories a day more for 8 weeks. People who tended to fidget gained only 3 pounds, but those who slouched in the chair gained 16 pounds! Yes, all small things count!

Temperature of the Environment

Do you know how the majority of energy is used in the body? It keeps the body temperature steady! If you live in a cool environment, to keep the body temperature steady, the body burns more calories. You know you get shivers when you are cold, right? It is because the body cannot make enough heat and is sending a signal to the muscles to move so that the body can generate more heat. If you live in a cooler environment with lighter clothes, you may lose extra 5 pounds of body fat just from sitting comparing to people who keep the room temperature at a very “comfortable” range.

Of course this may not be true for all. If you are a very inactive person and if your metabolism is very low from wrong dieting, your body may not be able to generate enough heat to keep your body warm. If this is the case, you need to re-ignite your metabolism by working out.

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