What is Intermittent Fasting?
Intermittent fasting (IF) is not starvation. If you are new to fasting, don’t let the word scare you. Starvation is the involuntary absence of food for a long time. This can lead to severe suffering or even death. It is neither deliberate nor controlled. On the other hand, fasting is the voluntary avoidance of food for spiritual, health, or other reasons. It’s done by someone who is not underweight and has enough stored body fat to live off. When done correctly, fasting should not cause suffering, and certainly never death. Food is easily available, but you choose not to eat it. This can be for any period of time, from a few hours (if you are a beginner start easy) up to a few days, or — with medical supervision — even a week or more. You may begin a fast at any time of your choosing, and you may end a fast at will too.
Anytime you are not eating, you are intermittently fasting. For example, you may fast between dinner and breakfast the next day, a period of approximately 12–14 hours. In that sense, intermittent fasting should be considered a part of everyday life. Consider the term “break-fast.” This refers to the meal that breaks your fast — which is done daily. Rather than being some sort of cruel and unusual punishment, the English language implicitly acknowledges that fasting should be performed daily, even if only for a short duration. Intermittent fasting is not something unusual but a part of everyday, normal life. It is perhaps the oldest and most powerful dietary intervention imaginable.
Fasting has been a practice throughout human evolution. Ancient hunter-gatherers didn’t have supermarkets, refrigerators, or food available year-round. Sometimes they couldn’t find anything to eat. As a result, humans evolved to be able to function without food for extended periods of time. In fact, fasting from time to time is more natural than always eating 3–4 (or more) meals per day. Fasting is also often done for religious or spiritual reasons, including in Islam, Christianity, Judaism and Buddhism.
Nowadays, IF is one of the world’s most popular health and fitness trends. People are using it to lose weight, improve their health, and simplify their lifestyles. Many studies show that it can have powerful effects on your body and brain, and it may even help you live longer.1
Let’s dive into a quick guide about fasting methods for beginners.
Intermittent Fasting Methods
Intermittent fasting is an eating pattern that cycles between periods of fasting and eating. It doesn’t specify which foods you should eat but rather when you should eat them. In this respect, it’s not a diet in the conventional sense but more accurately described as an eating pattern.
There are several different ways of doing intermittent fasting — all of which involve splitting the day or week into eating and fasting periods.2 During the fasting periods, you eat either very little or nothing at all.
These are the most popular methods:
The 16/8 Method: Also called the Leangains protocol, it involves skipping breakfast and restricting your daily eating period to 8 hours, such as 1–9 p.m. Then you fast for 16 hours in between.
Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day.
The 5:2 Diet: With this method, you consume only 500–600 calories on two non-consecutive days of the week, but eat normally the other 5 days. By reducing your calorie intake, all of these methods should cause weight loss as long as you don’t compensate by eating much more during the eating periods.
Many people find the 16/8 method to be the simplest, most sustainable, and easiest to stick to. It’s also the most popular.
The Five Stages of Intermittent Fasting and Their Benefits
When you fast, several things happen in your body on the cellular and molecular level. For example, your body adjusts hormone levels to make stored body fat more accessible. Your cells also initiate important repair processes and change the expression of genes.3
By 12 hours, you’ve entered the metabolic state called ketosis. In this state, your body starts to break down and burn fat. Some of this fat is used by the liver to produce ketone bodies. Ketone bodies, or ketones, serve as an alternative energy source for the cells of your heart, skeletal muscle, and brain, when glucose isn’t readily available. When you are fasting, ketone bodies generated by your liver partly replace glucose as fuel for your brain as well as other organs. This ketone usage by your brain is one of the reasons that fasting is often claimed to promote mental clarity and positive mood. Ketones produce less inflammatory products as they are being metabolized than glucose does, and they can even kick-start production of the brain growth factor BDNF.4 Ketones have also been shown to reduce cellular damage and cell death in neurons and can also reduce inflammation in other cell types.5
By 18 hours, you’ve switched to fat-burning mode and are generating significant ketones. As their level in your bloodstream rises, ketones can act as signalling molecules, similar to hormones, to tell your body to ramp up stress-busting pathways that reduce inflammation and repair damaged DNA, for example.
Within 24 hours, your cells are increasingly recycling old components and breaking down misfolded proteins linked to Alzheimer’s and other diseases.6 This is a process called autophagy. Autophagy is an important process for cellular and tissue rejuvenation — it removes damaged cellular components including misfolded proteins. When your cells can’t or don’t initiate autophagy, bad things happen, including neurodegenerative diseases, which seem to come about as a result of the reduced autophagy that occurs during aging.7
Tips for Beginners
Let’s consider the popular 16/8 IF method. To get started, begin by picking an 8-hour window and limit your food intake to that time span. Many people prefer to eat between noon and 8 p.m., as this means you’ll only need to fast overnight and skip breakfast but can still eat a balanced lunch and dinner, along with a few snacks throughout the day. Others opt to eat between 9 a.m. and 5 p.m., which allows plenty of time for a healthy breakfast around 9 a.m., a normal lunch around noon, and a light early dinner or snack around 4 p.m. before starting your fast. However, you can experiment and pick the time frame that best fits your schedule.
Try balancing each meal with a good variety of healthy whole foods, such as fruits, veggies, whole grains, and healthy fats. Drinking calorie-free beverages like water and unsweetened tea and coffee, even while fasting, can also help control your appetite while keeping you hydrated. On the other hand, binging or overdoing it on junk food can negate the positive effects associated with 16/8 intermittent fasting and may end up doing more harm than good to your health.
People who should not fast include those who are underweight or have eating disorders like anorexia, women who are pregnant or breastfeeding (they need extra nutrients for the child), and people under the age of 18 (they need extra nutrients to grow).