The popularity of intermittent fasting is on the rise. Searches for the term have been rising consistently with the greatest increase happening more recently. It is becoming a very popular method to lose weight and improve health, with very good results.
Intermittent fasting is in fact not new. It has been practiced throughout all of human history. The first humans practiced intermittent fasting simply because due to food scarcity, they had to sometimes go through extended periods of time without food, and this shaped the body’s response over time. Fasting has also been practiced in later ages as a way to achieve spiritual enlightenment.
With revolutions in agriculture and grazing, scarcity of calories has become a thing of the past in most nations and the idea of fasting as a dietary regimen has been largely left behind.
Only recently have dieticians and doctors rediscovering the metabolic benefits of fasting. When done right, intermittent fasting may provide huge benefits, including excess weight loss, reversal of type 2 diabetes and more.
So what is fasting, anyway?
Simply put, fasting is any period of time when you are voluntarily not eating. This can last from a few hours to several days or weeks. An intermittent fast is a period in which a person is fasting, followed by a period where that person is eating. A person might have breakfast and lunch followed by a period of fasting until breakfast (Break-Fast) the next day. This is a common fasting regimen.
Losing weight with intermittent fasting
The core principal of fasting for weight loss is to allow the body to burn through its stored energy by, for example, burning stored excess fat. The human body has evolved over time to fast for short periods of time – hours or days – without any negative health consequences.
Lets understand how fat is created. When we eat, we ingest more food energy than can be used at that particular moment. Some of this energy will be stored for future use. Insulin is the key hormone involved in the process of storing food energy.
When we eat, insulin will raise to help store the excess energy in two separate ways. Carbohydrates are broken down into individual glucose (sugar) units, which can be added to long chains to form glycogen, which is then stored in the liver or muscles. However, this is a very limited space for carbohydrate storage, and once the space is filled the liver will start to turn excess glucose into fat. Some of this fat will be stored in the liver, but most will be sent to other fat deposits around the body. There is almost no limit to how much fat can theoretically be stored across the body.
The key characteristic of these two complementary energy storage systems that we have in our body are that one is readily available and easy for the body to access (glycogen) but provides limited storage space, and the other is more difficult to access (body fat) but provides much larger storage space. To make a parallel with computing, this is like comparing the computer’s RAM memory (glycogen store) and the computer’s hard drive (body fat storage).
When you fast, the process is reversed. The insulin levels in the body drop, signalling the body to start burning stored energy. The levels of glucose in the blood will drop and the body will look to pull glucose out of storage to process into energy. The body will burn through the easiest source of energy first, glycogen, found in the liver and muscles. The glycogen stores may provide enough energy to power the body for about 24-36 hours. After that, the body has to switch to burning fat.
This means that the body mainly exists in two states: the fed state (insulin high) and the fasted state (insulin low). We are either storing energy or burning it. The more time you spend storing energy, the more likely you will be gaining weight and the more time you spend burning energy, the more likely you are to be losing weight. If both states are balanced, you maintain the same weight.
Intermittent fasting aims to increase the amount of time you spend burning energy, as opposed to storing it. This is the main objective of the fast and it is an absolutely healthy process that our bodies were designed to perform.
The benefits of intermittent fasting
While weight loss is the most evident benefit of intermittent fasting, there are several other potential benefits, some of which have been known for centuries. Researchers are conducting more and more studies on the benefits of intermittent fasting. Other benefits include: Potential reversal of type 2 diabetes (1) (2) (3), potentially improved concentration and mental clarity (4), potential increase of energy (note that digestion is one of the processes in the body that consumes the most energy) (5) (6), potentially improved cholesterol profile (7), possible reduction in the risk of Alzheimer’s disease (8) and possibly longer life (9).
Popular intermittent fasting regimens
Shorter fasts (<24 hrs)
There are plenty of ways to conduct your intermittent fasting. Shorter fasts can be done more frequently.
16 hour fast (16:8):
This fast regimen involves fasting for 16 hours and having an 8-hour window where you can have all your meals. This fast can be done daily or almost daily. This fast will usually involve skipping either breakfast or dinner, whichever you prefer. Usually a person will eat two or three meals within the 8-hour eating period.
20 hour fast (20:4):
This fasting regimen involves fasting for 20 hours and having a 4-hour eating window. In this fast a person could, for example, eat between 2:00pm and 6:00pm every day and fast for the rest of the time. Generally a person would eat one meal or two smaller meals within the eating window.
Longer fasts (>24 hrs)
This fasting regimen involves fasting from breakfast to breakfast (or dinner to dinner). If you have breakfast one morning you would then skip all meals until breakfast the next morning. You would therefore be eating once a day. This would be done two to three times per week.
2 day fast (5:2):
In this fast people will have an eating window of 5 days and fast for 2 straight days. However, on these two fasting days you are allowed to consume 500 calories on each day, either in one meal or spread throughout the day.
A variant of this fast regimen can also be done where a person will alternate between one day of regular eating and one day of fasting (max 500 cal) throughout the whole week.
In this regimen a person will who eats dinner on day 1 will fast for all of day 2 and only eat again at breakfast of day 3. This regimen may prove to have a more powerful effect on weight loss.
Fasts lasting longer than 36 hours should be accompanied of medical advice and monitoring.