Intermittent fasting (IF) is currently one of the world's most popular health and fitness trends.
Many studies show that it can have powerful effects on your body and brain and may even help you live longer (123).
This is the ultimate beginner's guide to intermittent fasting.

Knife, Fork and Plate
SUMMARYIntermittent 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.

These are the most popular methods:
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.
SUMMARYThere are several different ways to do intermittent fasting. All of them split the day or week into eating and fasting periods.

  • Insulin: Insulin sensitivity improves and levels of insulin drop dramatically. Lower insulin levels make stored body fat more accessible (8).
  • Gene expression: There are changes in the function of genes related to longevity and protection against disease (1112).

Weight loss is the most common reason for people to try intermittent fasting (13).
Additionally, intermittent fasting changes hormone levels to facilitate weight loss.
Because of these changes in hormones, short-term fasting may increase your metabolic rate by 3.6–14% (1415).
Another study showed that intermittent fasting causes less muscle loss than the more standard method of continuous calorie restriction (16).
SUMMARYIntermittent fasting may slightly boost metabolism while helping you eat fewer calories. It’s a very effective way to lose weight and belly fat.

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 (113).
  • Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases (171819).
  • Cancer: Animal studies suggest that intermittent fasting may prevent cancer (22232425).
  • 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 (26272829).
  • Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats lived 36–83% longer (3031).

Intermittent fasting can make things easier, as you don't need to plan, cook or clean up after as many meals as before.
SUMMARYOne of the major benefits of intermittent fasting is that it makes healthy eating simpler. There are fewer meals you need to prepare, cook and clean up after.

Intermittent fasting is certainly not for everyone.
In these cases, it can be downright harmful.

Should Women Fast?

For example, one study showed that it improved insulin sensitivity in men, but worsened blood sugar control in women (33).
For these reasons, women should be careful with intermittent fasting.
SUMMARYPeople who are underweight or have a history of eating disorders should not fast. There is also some evidence that intermittent fasting may be harmful to some women.

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 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.

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

1. Can I Drink Liquids During the Fast?


2. Isn't It Unhealthy to Skip Breakfast?


3. Can I Take Supplements While Fasting?


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?


6. Will Fasting Slow Down My Metabolism?

No. Studies show that short-term fasts actually boost metabolism (1415). However, longer fasts of 3 or more days can suppress metabolism (36).

7. Should Kids Fast?

Allowing your child to fast is probably a bad idea.

Chances are that you've already done many intermittent fasts in your life.
If you've ever eaten dinner, then slept late and not eaten until lunch the next day, then you've probably already fasted for 16+ hours.
Some people instinctively eat this way. They simply don't feel hungry in the morning.
Another approach is to simply fast whenever it’s convenient — simply skip meals from time to time when you're not hungry or don't have time to cook.
SUMMARYIt’s recommended to start with the 16/8 method, then perhaps later move on to longer fasts. It’s important to experiment and find a method that works for you.

Intermittent fasting is not something that anyone needs to do.
If you don't like the idea of fasting, then you can safely ignore this article and continue to do what works for you.