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.

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.

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 method, you consume only 500–600 calories on two nonconsecutive 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 Cells and 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, to name a few.
• 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.

Health Benefits

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.
• 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.
• Heart health: Intermittent fasting may reduce “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance — all risk factors for heart disease.

Makes Your Healthy Lifestyle Simpler

Eating healthy is simple, but it can be incredibly hard to maintain.

One of the main obstacles is all the work required to plan for and cook healthy meals.

Intermittent fasting can make things easier, as you don’t need to plan, cook or clean up after as many meals as before.

For this reason, intermittent fasting is very popular among the life-hacking crowd, as it improves your health while simplifying your life at the same time.

Safety and Side Effects

Hunger is the main side effect of intermittent fasting.

You may also feel weak and your brain may not perform as well as you’re used to.

This may only be temporary, as it can take some time for your body to adapt to the new meal schedule.

If you have a medical condition, you should consult with your doctor before trying intermittent fasting.

This is particularly important if you:

• Have diabetes.
• Have problems with blood sugar regulation.
• Have low blood pressure.
• Take medications.
• Are underweight.
• Have a history of eating disorders.
• Are a woman who is trying to conceive.
• Are a woman with a history of amenorrhea.
• Are pregnant or breastfeeding.

All that being said, intermittent fasting has an outstanding safety profile. There is nothing dangerous about not eating for a while if you’re healthy and well-nourished overall.

Frequently Asked Questions

Here are answers to the most common questions about intermittent fasting.

1. Can I Drink Liquids During the Fast?

Yes. Water, coffee, tea and other non-caloric beverages are fine. Do not add sugar to your coffee. Small amounts of milk or cream may be okay.

Coffee can be particularly beneficial during a fast, as it can blunt hunger.

2. Isn’t It Unhealthy to Skip Breakfast?

No. The problem is that most stereotypical breakfast skippers have unhealthy lifestyles. If you make sure to eat healthy food for the rest of the day then the practice is perfectly healthy.

3. Can I Take Supplements While Fasting?

Yes. However, keep in mind that some supplements like fat-soluble vitamins may work better when taken with meals.

4. Can I Work out While Fasted?

Yes, fasted workouts are fine. Some people recommend taking branched-chain amino acids (BCAAs) before a fasted workout.

5. Will Fasting Cause Muscle Loss?

All weight loss methods can cause muscle loss, which is why it’s important to lift weights and keep your protein intake high. One study showed that intermittent fasting causes less muscle loss than regular calorie restriction.

6. Will Fasting Slow Down My Metabolism?

No. Studies show that short-term fasts actually boost metabolism. However, longer fasts of 3 or more days can suppress metabolism.

7. Should Kids Fast?

Allowing your child to fast is probably a bad idea.