Intermittent fasting is currently 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 may even help you live longer, lose weight faster and look better.
This is the ultimate guide to intermittent fasting.
What is Intermittent Fasting?
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.
Common intermittent fasting methods involve daily 16-hour fasts or fasting for 24 hours either everyday of the week or once or twice.
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 meals per day.
Types of Intermittent Fasts
There are several different ways of doing intermittent fasting — all of which involve splitting the day or week into eating and fasting periods.
During the fasting periods, you eat either very little or nothing at all.
These are the most popular methods:
The 16/8 method: This 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.
How it affects your hormones
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.
Here are some changes that occur in your body when you fast:
Human Growth Hormone (HGH): The levels of growth hormone skyrocket, increasing as much as 5-fold. This has benefits for fat loss and muscle gain.
Insulin: Insulin sensitivity improves and levels of insulin drop dramatically. Lower insulin levels make stored body fat more accessible.
Cellular repair: When fasted, your cells initiate cellular repair processes. This includes autophagy, where cells digest and remove old and dysfunctional proteins that build up inside cells.
Gene expression: There are changes in the function of genes related to longevity and protection against disease.
These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.
How fasting affects weight loss
Weight loss is the most common reason for people to try intermittent fasting.
By making you eat fewer meals, intermittent fasting can lead to an automatic reduction in calorie intake.
Additionally, intermittent fasting changes hormone levels to facilitate weight loss.
In addition to lowering insulin and increasing growth hormone levels, it increases the release of the fat burning hormone noradrenaline.
Because of these changes in hormones, short-term fasting may increase your metabolic rate.
By helping you eat fewer and burn more calories, intermittent fasting causes weight loss by changing both sides of the calorie equation.
Studies show that intermittent fasting can be a very powerful weight loss tool. However, keep in mind that the main reason for its success is that intermittent fasting helps you eat fewer calories overall. If you binge and eat massive amounts during your eating periods, you may not lose any weight at all.
The health benefits of fasting
Many studies have been done on intermittent fasting, in both animals and humans.
Here are the main health benefits of intermittent fasting:
Weight loss: As mentioned above, intermittent fasting can help you lose weight and belly fat, without having to consciously restrict calories.
Insulin resistance: Intermittent fasting can reduce insulin resistance, lowering your blood sugar, which should protect against type 2 diabetes.
Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases.
Heart health: Intermittent fasting may reduce “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance — all risk factors for heart disease.
Cancer: Animal studies suggest that intermittent fasting may prevent cancer.
Brain health: Intermittent fasting increases the brain hormone BDNF and may aid the growth of new nerve cells. It may also protect against Alzheimer’s disease.
Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats lived 36–83% longer.