Intermittent fasting (IF) 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 (1, 2, 3Trusted Source). This is the ultimate beginner's guide to intermittent fasting.
What Is Intermittent Fasting (IF)?
Intermittent fasting (IF) 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, twice per week.
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.
Summary Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It’s currently very popular in the health and fitness community.
Intermittent Fasting Methods
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: 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 methods, 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.
Summary There are several different ways to do intermittent fasting. All of them split the day or week into eating and fasting periods.
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, to name a few (4Trusted Source, 5Trusted Source, 6Trusted Source, 7Trusted Source)
Insulin: Insulin sensitivity improves and levels of insulin drop dramatically. Lower insulin levels make stored body fat more accessible (8Trusted Source).
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 (9Trusted Source, 10Trusted Source
Gene expression: There are changes in the function of genes related to longevity and protection against disease (11Trusted Source, 12Trusted Source).
These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.
Summary When you fast, human growth hormone levels go up and insulin levels go down. Your body’s cells also change the expression of genes and initiate important cellular repair processes.
A Very Powerful Weight Loss Tool
Weight loss is the most common reason for people to try intermittent fasting (13Trusted Source).
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 norepinephrine (noradrenaline). Because of these changes in hormones, short-term fasting may increase your metabolic rate by 3.6–14% (14Trusted Source, 15Trusted Source).
A 2014 review study found that this eating pattern can cause 3–8% weight loss over 3–24 weeks, which is a significant amount, compared to most weight loss studies (1).
According to the same study, people also lost 4–7% of their waist circumference, indicating a significant loss of harmful belly fat that builds up around your organs and causes disease (1).
Another study showed that intermittent fasting causes less muscle loss than the more standard method of continuous calorie restriction (16Trusted Source).
Summary: By helping you eat fewer and burn more calories, intermittent fasting causes weight loss by changing both sides of the calorie equation. Keep in mind that research is still in its early stages. Many of the studies were small, short-term or conducted in animals. Many questions have yet to be answered in higher quality human studies (32Trusted Source). Intermittent fasting can have many benefits for your body and brain. It can cause weight loss and may reduce your risk of type 2 diabetes, heart disease and cancer. It may also help you live longer.
Many studies have been done on intermittent fasting, in both animals and humans.
These studies have shown that it can have powerful benefits for weight control and the health of your body and brain. It may even help you live longer.
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 (1, 13Trusted Source).
Insulin resistance: Intermittent fasting can reduce insulin resistance, lowering blood sugar by 3–6% and fasting insulin levels by 20–31%, which should protect against type 2 diabetes (1).
Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases (17Trusted Source, 18Trusted Source, 19Trusted Source).
Heart health: Intermittent fasting may reduce “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance — all risk factors for heart disease (1, 20Trusted Source, 21)
Cancer: Animal studies suggest that intermittent fasting may prevent cancer (22Trusted Source, 23Trusted Source, 24Trusted Source, 25Trusted Source)
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 (26Trusted Source, 27Trusted Source, 28Trusted Source, 29Trusted Source)
Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats lived 36–83% longer (30, 31).
Summary Keep in mind that research is still in its early stages. Many of the studies were small, short-term or conducted in animals. Many questions have yet to be answered in higher quality human studies (32Trusted Source). Intermittent fasting can have many benefits for your body and brain. It can cause weight loss and may reduce your risk of type 2 diabetes, heart disease and cancer. It may also help you live longer we just don't know. People with certain medical conditions should not fast without consulting with a doctor first.
Read the rest of the article: Intermittent Fasting 101 The Ultimate Beginners Guide