- Intermittent fasting is an eating style where you eat within a specific time period and fast the rest of the time.
- Intermittent fasting can be an effective way to manage your body weight. But research shows it has tons of other health benefits, too—like more energy, brain power and cellular protection.
- The best part? There are tons of different ways to implement this practice, including changing your eating window and intermittent fasting schedule.
Intermittent fasting, also called IF, is pretty simple. You eat within a shortened period of time, and you fast the rest of the time. If you’re not eating right now, you’re fasting. And if you extend your fast a bit longer, you can benefit from it.
Keep reading to learn how intermittent fasting works, how it can transform your eating habits and how you can get started today.
What is intermittent fasting?
When you fast intermittently, you eat within a shortened time window—usually 8-10 hours. Here’s what that might look like:
- Skip breakfast.
- Around noon, break your fast and have your first meal.
- Eat dinner. Maybe treat yourself to dessert.
- Stop eating by 8 p.m.
- Repeat this schedule the next day.
Why do people go long periods of time without eating? Although weight management is definitely one of the benefits of intermittent fasting, it’s not strictly dieting. It’s an eating schedule that has big payoffs over time, like regulating your insulin levels, protecting against disease and—yup, helping you stay at a healthy weight.
This might go against what you’ve heard about eating frequency in the past. Skipping a meal won’t send your body into “starvation mode” or necessarily inhibit your fat loss goals. And although there’s nothing wrong with eating breakfast, there are major benefits to giving your body an extended break between meals.
Related: Types of Fasting Diets and How to Choose the Right One
How does intermittent fasting work?
We’re going to talk about biology for a second, then explain what it means. When you eat, a lot happens in your body:
- Depending on what you’ve eaten, your blood glucose (sugar) levels may rise.
- Your pancreas produces a hormone called insulin.
- Insulin tells your cells to fuel up on glucose and tells your fat stores to stay in your fat cells.
- Your body releases hormones like cholecystokinin (CCK) and leptin, which signal when you’re full.
However, when you eat a lot of carbs and sugar, they don’t have as potent an effect on the release of CCK as protein and fats do, so your body is less likely to send “I’m full!” signals. Eating frequently and eating excessively in one sitting is more likely to happen. Your pancreas has to work overtime to release insulin and all that extra glucose from the carbs and sugar gets stored as body fat.
Over time, those factors can increase your risk of weight gain, insulin resistance and diseases like type 2 diabetes and cancer. Yikes.
Intermittent fasting gives your body time to reset. When you take a break between meals, your glucose levels remain stable, your insulin levels drop and your body has a chance to clean up shop—all of which can support major benefits like weight management and longevity.
Related: How to Do Intermittent Fasting for Weight Management
Types of intermittent fasting schedules
There is no one-size-fits-all approach to intermittent fasting. Some opt for daily fasting. Others prefer to only fast a few days of the week.
Let’s take a closer look at some of the more popular methods, including a protocol that calls for a full day of not eating.
You eat all of your daily calories within a shortened period (typically a 6-8 hour window) and fast the rest of the time. This type of fasting schedule is great for those who don’t usually find themselves hungry in the morning when they wake up.
Fasting for 12 hours
Looking for a type of intermittent fasting for beginners? The 12:12 protocol is a great place to start. It’s less restrictive than other methods, as you fast for 12 hours a day and have an equal amount of time to eat.
Developed by Brad Pilon, this intermittent fasting schedule requires you to choose one or two non-consecutive days per week where you will fast for a full 24-hour period.
You eat normally five days a week. On the other two days, you restrict calories by eating 500-600 calories per day.
You fast every other day, and eat normally on non-fasting days.
Weekly 24 hour fast
The benefits of intermittent fasting for longer periods make a weekly 24-hour fast a strategy worth trying. You can break up the week by taking a day off from eating, or select a specific day that fits your schedule and lifestyle.
You don’t have to eat three meals a day. For example, you can say goodbye to breakfast and wait until the afternoon to break your fast. Or, if you’re not feeling particularly hungry at lunch, skip it.
The Warrior Diet is very similar to OMAD (one meal a day). You fast for 20 hours a day and consume a large meal at night. However, you are allowed to eat small amounts of certain foods during those intermittent fasting hours, including fruits, vegetables and broth.
Who should avoid intermittent fasting?
Is intermittent fasting healthy for everyone? The short answer is no.
If you are pregnant, breastfeeding, elderly, have a history of disordered eating, have a medical condition or are taking medication, speak with your healthcare practitioner about whether to engage in intermittent fasting.
How to get started with fasting
Ready to change up your eating schedule? One of the best parts of intermittent fasting is that it’s really easy to adapt to your lifestyle.
You can follow the same eating pattern every day, or you can fast just a few times a week. You can even customize the amount of time you spend between meals—which is good news if you only occasionally want to follow a fasting schedule. Keep in mind that anybody with a current medical condition or using medication should talk to their healthcare practitioner before starting intermittent fasting.
Choosing a time window
Take time to find the perfect fit, pay attention to how you feel and don’t be afraid to experiment with different fasting schedules.
For example, if you can’t stomach the thought of ditching breakfast, just switch your fasting period. Eat a full meal around 8 a.m., and stop eating around 4 p.m. The good news: This is still a 16-hour fast. The best news: You can change your fasting schedule to suit your needs (and still have breakfast).
Choosing a meal plan
You don’t have to follow keto to benefit from fasting. But one of the side effects of intermittent fasting is that it supports your body’s metabolic switch into the fat-burning state of ketosis. Keep it going by eating low-carb, high-fat foods when you break your fast. People report having fewer cravings and a reduced appetite on keto, so it pairs well with an intermittent fasting diet.
During your eating window, if you get hungry between meals, try snacking on keto-friendly foods and avoid the sugar crash—we like hard-boiled eggs, avocados, or fat-fueled coffee
One note on calorie intake: Even if you don’t care about weight management, you might naturally put yourself in a caloric deficit. In the short-term, cutting excess calories from your diet may help you stay at a healthy weight. But long-term calorie restriction can mess with your metabolic rate and hormone function. That’s why you don’t want to stay in a caloric deficit forever. If you’re feeling fatigued, sluggish and not yourself, talk to your doctor and consider using a food tracker app to make sure you’re eating enough to stay energized and awesome.
What can you eat while intermittent fasting?
If you’re a fasting purist, only drink water during your fast. You aren’t consuming any calories, so you’re helping ensure your body stays in a fasted state and activates autophagy.
That means that during a fast, you want to stay as close to zero calories as possible. But that’s easier said than done, especially if you’re used to eating or taking supplements at certain times or reaching for snacks when you’re stressed. And if you’re experimenting with more flexible styles of fasting, such as 5:2, you might eat up to 600 calories in a day.
Can’t start your day without a hot cup of coffee? The good news is that when you’re intermittent fasting, coffee and tea are fine—just hold the milk and sugar.
Most experts agree that drinking a cup of tea or coffee during intermittent fasting won’t dramatically impact your results. In fact, the caffeine can help suppress your appetite (and perk you up in the morning, obviously).
But if you want to maximize the benefits of autophagy, stay as close to zero calories as possible during your fasting window.
How intermittent fasting affects your cells and hormones
Intermittent fasting can have a major impact on your cells, hormones and internal systems. Here are a few ways how:
Research shows that fasting results in increased peak HGH (human growth hormone) concentrations in sleep. HGH is naturally produced by the pituitary gland and plays a key role in cell regeneration and growth.
Implementing IF can be beneficial for those with insulin resistance. Research shows an IF regimen can reduce fasting insulin and insulin resistance in overweight and obese adults.
Over time, your cells naturally accumulate damaged components and waste. This junk can interfere with cellular function. In rodent studies, intermittent fasting has been shown to promote a process called autophagy, which is what happens when your body clears out the junk so your cells can work even better.
In rodent studies, alternate-day fasting reduced inflammatory gene expression, as well as total triglyceride concentrations.
Fasting for weight loss
If you’re trying to lose weight, fasting can be an effective tool. It’s an easy way to control the amount of food you eat, and you’ll have more time to be active. Plus, combining fasting with a high fat, low-carb diet can further enhance your efforts to reduce your body fat levels and reach your body composition goal.
Tips for maintaining intermittent fasting
How can you implement and stick to intermittent fasting? Here are a few tips that can help you stay on the right path:
- Start your fast after dinner so a significant portion of your fasting period occurs during sleep
- Eat satiating meals that contain quality fats and protein
- Drink coffee to help blunt your appetite and give you a caffeine boost
- Stick to a fasting schedule that aligns with your lifestyle
- Stay active and engaged so you’re not thinking about food
Benefits of intermittent fasting
Some people think of intermittent fasting for weight loss. It’s not that simple—you need to eat! But when you restrict your eating window, you naturally give your body a break from digestion. That translates to a few key intermittent fasting benefits:
Everything from your hormones to your blood sugar affects what shows up on the scale. In animal and human studies, intermittent fasting has been shown to help prevent insulin resistance and leptin resistance, which may assist with weight management.
Furthermore, a review on intermittent fasting programs determined both alternate-day fasting and whole-day fasting trials were effective at reducing body weight, body fat and total triglycerides.
Research suggests intermittent fasting can be beneficial for inflammation. A study conducted on 40 volunteers celebrating Ramadan—a holy month for Muslims when no food or drink is ingested from dawn to dusk for 30 days in a row—found that prolonged intermittent fasting has a positive effect on the inflammatory status of the body.
A study conducted on 16 obese men and women found that eight weeks of alternate-day fasting reduced triglyceride levels by 32%. A separate study also supports the benefits of fasting for heart health, as a three-week fasting diet in extremely obese patients resulted in a significant decrease and normalization of blood pressure.
Could fasting provide a boost for your brain? A rodent study found that alternate-day fasting improved brain functions and structures.
In rodent studies, intermittent fasting has been shown to increase lifespan and protect against disease.
Potential side effects of intermittent fasting
What are some of the potential downsides of intermittent fasting? Hunger is one of the most common side effects of going prolonged periods without eating. In fact, a year-long study conducted on 112 participants found that the fasting group reported higher hunger scores than those who consumed a low-calorie diet with continuous calorie restriction.
In addition, if you’re used to eating throughout the day, switching up your schedule may be a bit of a mental challenge. Don’t get discouraged, though. Like any lifestyle change, it takes time to adjust and adapt.
The bottom line: Everyone has different dietary needs based on personal factors like activity level and body composition. Your body will tell you if you need to adjust your intermittent fasting plan, and this eating pattern isn’t for everyone. That’s perfectly okay. What matters is that you’re doing what helps you feel your best, day in and day out.
Ready to fuel up after your latest fast? These 19 tasty recipes provide the quality fats and protein your body needs to thrive in a single meal.
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This is an updated version of an article originally published December 2019.