Intermittent fasting (IF) part 1

Every year there is a new diet trend going around and this year intermittent fasting has become very popular under gym-goers and health-gurus. Some people swear to have lost kilos of fat with intermittent fasting while other claim it helped them build muscle after their results were stagnating for some time already. So what is intermittent fasting exactly and how does it work?

What is intermittent fasting?

It must be clear that intermittent fasting (IF) is not a diet. A diet is a predetermined plan of what you eat on a day while IF means you eat during certain times of the day only. IF is therefore more similar to an eating pattern, just as eating 3 or 6 meals a day is. The IF eating pattern consists of a short period where you eat, followed by a longer period where you don’t eat at all (fast). There are many different eating patterns possible with IF, but the most popular are fasting for 24 hours twice a week (5–2 pattern) or fasting for a period of 16 hours a day (16–8 fasting). A combination of these two patterns is also possible.

How does intermittent fasting work?

Basic instinct tells you that only eating for a short period of time and not eating for a longer period of time would probably lead to eating fewer calories which would result in a caloric deficit (burning more calories than you eat) and weight loss. While this is true, the real idea behind IF is different.

During the period of time that you don’t eat your body will use glycogen stored in the liver and muscles as fuel. It will take about 6 to 8 hours to completely deplete these stores after which fats are used as the primary source of energy. By fasting for more than 8 hours per day you will therefore burn stored fat resulting in weight loss.

But what about the time that you do eat, don’t you gain back the same amount of fat? You would think this is true if you approach the body as a something simple, but due to complex processes involving hormones the reality is different. By not eating for longer periods of time your body becomes more sensitive for insulin which is a hormone that helps cells absorb glucose from the blood. The more sensitive your body is to insulin, the less insulin it will produce, and the harder it will be to store energy in fat cells.

The surplus of available energy can now be used more efficiently, for example for recovery and building muscle. This, together with an increase in human growth hormone production that is promoted by the fasting, will result in a better recovery and an increase in muscles.

Intermittent fasting, if applied correctly, can help you in several ways:

  1. Burn stored fat as a source of energy
  2. Increase the production of human growth hormone
  3. Increase sensitivity to insulin
  4. Make it harder for your body to store energy as fat
  5. More efficient use of nutrients resulting in an increase of muscle mass and better recovery

The story is all positive so far for intermittent fasting, but if applied in an incorrect way it can do more harm than good. In part 2 we will explore some of the problems with IF.

Originally published at