What Is Intermittent Fasting? Explained in Simple Terms (2025)

Intermittent fasting involves alternating cycles of eating and going without food. Depending on the type, you may try intermittent fasting at different times of day and change how many calories you eat.

Intermittent fasting is currently one of the world’s most popular health and fitness trends.

Research shows that this different type of eating pattern can help you with weight loss, improve metabolic health, manage stress, help protect against disease and other conditions, and perhaps even help you live longer.

This article explains what intermittent fasting is and why you should care.

Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting.

It does not say anything about which foods to eat, but rather when you should eat them.

There are several different intermittent fasting methods, all of which split the day or week into eating periods and fasting periods.

Most people already “fast” every day, while they sleep. But intermittent fasting as a way of eating is different and can be quite simple. This may include:

• extending your sleeping fast a little longer
• skipping breakfast
• eating your first meal at noon
• eating your last meal at 8 pm

Anecdotally, many people report feeling better and having more energy during a fast. But other people report feeling worse and less energic.

Hunger is common but tends to be more of an issue for people who follow a pattern of fasting for an entire day, multiple times per week.

No food is allowed during the fasting period, but you can drink water, coffee, tea, and other noncaloric beverages.

Some forms of intermittent fasting allow small amounts of low calorie foods during the fasting period.

Taking supplements is generally allowed while fasting, as long as there are no calories in them.

All sorts of processes in the body change when we don’t eat for a while, in order to allow our bodies to survive during a period of famine. This relates to how our bodies work with hormones, genes, and important cellular repair processes.

You can experience reductions in blood sugar and insulin levels when fasting. It can also lead to an increase in human growth hormone, an important hormone produced by your pituitary gland that helps regulate growth in children and also improves muscle growth, strength, and lean body mass.

But there are other health benefits, too.

Can intermittent fasting help with weight loss?

Many people do intermittent fasting to lose weight, as it’s an effective way to restrict calories and burn fat.

Others do it for metabolic health benefits, as it can improve various risk factors and health markers.

Does intermittent fasting help protect against other diseases and conditions?

Some research also suggests that it may help protect against other health conditions and diseases.

These may include:

• heart disease
• type 2 diabetes
• cancer
• Alzheimer’s disease

But more clinical research is needed to determine how intermittent fasting might protect against different diseases and health conditions.

Fasting may help you live longer

There’s also some evidence that intermittent fasting can help you live longer. Some studies also show that it may extend your life as effectively as calorie restriction.

A 2021 clinical research shows that even mild intermittent fasting — along with healthy nutrition, movement, sleep patterns, and stress management — could help you live longer (decrease your biological age, per the study) by a little more than 3 years.

Intermittent fasting has become trendy in the past few years. You can try different types or methods to change the duration and timing of your daily fasting hours.

Here are some of the most popular ones:

• The 16/8 Method: You have a fixed window of eating 8 hours each day. You don’t eat any food for the remaining 16 hours, but you can drink water, plain coffee, or tea. Read more here.
• The 5:2 Diet: During 2 days of the week, eat only about 500–600 calories. For the other 5 days of the week, you eat as usual and don’t have to think about restricting calories.
• Eat-Stop-Eat: Once or twice a week, don’t eat anything from dinner one day until dinner the next day (a 24-hour fast).

There are many other variations, as well.

You can read more here about specific tips that can help you decide on and follow an intermittent fasting schedule.

This type of intermittent eating and not eating isn’t for everyone.

You may experience mood swings, hunger, and challenges in finding the best routine when trying out intermittent fasting and deciding on a schedule that works for you.

Certain meal plans and fasting methods may work better for some people versus others. Talking with your healthcare team and nutritionist or dietician (if you have access to one) may be a good first step in determining what might work best for you.

You can read more here about the pros and cons of intermittent fasting.

As long as you stick to healthy foods, restricting your eating window and fasting from time to time can have some good health benefits. It’s an effective way to lose fat and improve metabolic health, while simplifying your life at the same time.