How does Human Metabolism Work?

Our Metabolism is the rate at which the body uses energy to support all basic functions essential to sustain life, plus all energy requirements for additional activity and digestive processes.

Human metabolism is basically made up of three parts:

Physical activity 20-25%

Thermic effect of food 10%

Resting Metabolism 70%

1. Resting Metabolic Rate (RMR)

This is the amount of calories needed to run all essential functions and chemical reactions while in a rested and quiet state. RMR is the largest part of total metabolism and accounts for 65 - 75% of calories burned in a day.

If lean weight is lost from the body through increased protein metabolism the RMR decreases. This often happens when people go on a strict diet, the body is forced into what's known as a "negative nitrogen balance" which means more protein is lost than what is replaced due to less protein/energy intake. This imbalance causes a gradual loss in lean weight thus lowering the RMR.

Many dieters limit the amount of lean weight loss with some type of intense exercise in order for muscles to develop a need to hold onto more protein forcing the body to take more energy from fat stores. Learn more here!

2. Thermic Effect of Food (TEF)

The body uses energy to digest and absorb the nutrients present in the food we eat. The rate of energy used for the TEF is about 10%, it can be increased depending on the composition of each meal.

The TEF causes much confusion when dieters calculate calories in and out. For example;

If we overeat the TEF actually increases due to more food to digest, the stomach and intestines have to work harder and longer. It means if we ate an extra 3500 calories ( number of calories per pound of fat ) we wouldn't actually gain 1 pound of body fat because the TEF has to be accounted for, we would gain less.

The opposite also happens if we cut 3500 calories to lose 1 pound. The TEF decreases because there would be less food/nutrients to process so energy expenditure would reduce thus we would lose less than a pound in weight.

Calories do count but our body has sophisticated mechanisms to balance energy within the body to enable us hold onto as much energy as possible for a time when starvation may occur!

3. Physical activity

The amount of energy the body burns during daily activities such as exercise, recreation, work, housework, etc. Daily physical activities account for 20 - 40% of calories burned each day. This part will vary depending on the individual and how active they are each day. A sedentary person will require less calories to maintain weight than a busy worker in a construction site!

It is here where we can have the greatest effect on metabolism. The intensity, frequency and duration of any activity all have an effect on metabolism.

If you would like to learn more about losing weight and speeding up your metabolism in a healthy way, I suggest you check out Tom Venuto's new program. The book tends to be more for women in their mid 30's than for men, but is still an excellent resource to have.