The different types of intermittent fasting

Written by Aly Owen

Medically reviewed by Josie Porter, RD

Published on May 18, 2023 | Updated on May 3, 2024

So you’ve heard about intermittent fasting. The “magic” eating routine that might give you all the same health benefits of a calorie restriction diet — like improving heart and brain health while reducing inflammation and the risk of type 2 diabetes — without the whole “watch what you eat” and “hands off the cookie jar” thing. 

(Psst, we’ll let you in on a little secret: It’s not magic; it’s science. We’ll fill you in later.)

If you’re intrigued by the concept of focusing on when you eat rather than what you eat but don’t know where to go from there, you’ve come to the right place. There are loads of different intermittent fasting types, and the key to success lies in figuring out which one works best for you. This isn’t a one-size-fits-all situation. (When is it ever?!)

To help you out, we’ve outlined all the different types of intermittent fasting so you have everything you need to find the perfect fit for your body, goals, and lifestyle. 

Key takeaways

• There are tons of fasting types you can choose from if you’re interested in intermittent fasting.
• The approach you choose should be guided by what’s right — and safe — for your body, needs, preferences, and lifestyle. 
• If you’re just starting out with fasting, we recommend kicking things off with a time-restricted eating method like 14:10 or 16:8. 
• A longer fast doesn’t mean better results, and we don’t recommend fasting longer than 18 hours without medical approval and supervision. 
• There is no one-size-fits-all approach to fasting, so what’s effective or difficult for one person may not play out similarly for another. 

Types of intermittent fasting explained 

So, what are the different types of intermittent fasting? 

You’ve probably tried one without realizing it. Maybe you overslept and had to rush to work without having breakfast, so your first meal was that afternoon lunch meeting. Or maybe you were so full from one meal — Thanksgiving, anyone? — you skipped the next one.

Some intermittent fasting plans involve restricting your eating to certain timing windows, some involve fasting some days and not others, and some involve super intense isolated fasts … but the core of any fasting plan is that it involves watching the clock rather than what’s on your plate: it’s about when you eat, not what you eat. 

There’s no right way or one way to do it — and heads up, it’s not safe or effective for everyone (we’ll explain later) — so it’s all about finding which approach feels right to you. To learn more about all the plans we cover below, figure out which one(s) might be your perfect match, and get tips and support during every step of your journey, take our SIMPLE quiz today.

1. Time-restricted eating 

When most people think about the different types of intermittent fasting, they’re often thinking about different approaches to time-restricted eating. In other words, all the different ways you could divide each day between an “eating window” and a “fasting window.”

The short story: It’s simple. For some of the day, you don’t eat or drink anything with calories (water, tea, and coffee without milk, cream, or sugar are okay). For the rest of the day, you can. 

The longer story: Some time-restricted eating approaches are easier and potentially safer, and the more “hardcore” ones aren’t really more effective. Likewise, as with any food routine, you still want to ensure your body, mind, and soul get everything they need during that eating window. For the best results, that means prioritizing nutrient-dense, health-promoting foods like leafy vegetables, lean protein, calcium-rich foods, and healthy fats like seeds and nuts. (But don’t worry: No foods are completely off-limits, and one of the major selling points of intermittent fasting is that you can have your cake and eat it, too, as long as you don’t go overboard!)

A major pro of time-restricted eating approaches is that you can structure your eating / fasting schedule as you please. Can’t live without that morning muffin? Skip dinner the night before, or just have it earlier. Can’t imagine not eating alongside Top Chef reruns at night? Skip breakfast. 

This style-it-your-way accessibility is why time-restricted eating approaches are our — and our users’ — intermittent fasting favorites. You get freedom and flexibility without compromising on results or risking your safety.

While you can, in theory, restrict your eating to any window, there are four standard options. 

1. Intermittent fasting 14:10 

With a 14:10 fasting schedule, you’re fasting for 14 hours and eating within a 10-hour window. Since sleeping will naturally cover at least 7–8 of those, it’s a perfect intro to fasting — all you need to do is smush your meals slightly closer together. 

You can also adjust when your eating window hits so it meshes with your daily schedule. No need to sacrifice that Monday morning pastry that makes work more bearable, and equally, there’s no need to sacrifice that wine and whine evening on Thursdays. 

While there hasn’t been as much research into this fasting approach, some research has linked it to weight loss and better metabolic health [1], and lots of our users report it can be helpful for losing weight, too. Plus, a shorter fasting window can mean a reduced risk of side effects. 

2. Intermittent fasting 16:8

With 16:8 intermittent fasting, you’re fasting for 16 hours and eating within an 8-hour window. Anyone who has bumped into someone from high school while running an errand knows even a little extra time can feel like a lifetime. But when you factor in sleeping, you really just need to make peace with eating a late breakfast or early dinner. Sure, you can skip a meal … but you don’t have to. 

The 16:8 approach is the most common intermittent fasting method studied in existing research, and there’s a lot of evidence that backs it. If you’re looking for a routine that might support weight loss, fat loss, and heart health, you might lock in here.[2,3,4]

3. Intermittent fasting 18:6

Yep, you guessed it, an 18:6 fasting schedule involves fasting for 18 hours and eating within a 6-hour window. Now it’s starting to get dicey: You’ll need to skip at least one meal because eating the equivalent of three meals in six hours is not super comfy and could lead to overeating. 

With all those fasting hours and a mere six to meet your nutritional needs for the day, this fasting routine is not for beginners. We recommend only attempting it if you’re already used to fasting and have both a good idea of how to manage it around your schedule and a strategy for safe, effective meal planning. 

Some studies suggest a 6-hour eating window could lower blood pressure, lead to weight loss, and improve health overall [5], though others suggest it could cause undesirable changes in resting energy expenditure and BMI.[6] 

4. Intermittent fasting 20:4

The 20:4 fasting schedule involves fasting for 20 hours and eating within a 4-hour window. It’s tough. While you can still choose the timing of your eating window and, to an extent, what you eat during it, this routine requires extra careful consideration around meal planning and nutrition. It may also mean rearranging certain lifestyle elements, like exercise. 

The Warrior Diet is a version of this routine. With this approach, you begin your fast overnight and break it for a 4-hour eating window in the evening. 

Our bottom line is that you shouldn’t do any fast lasting longer than 18 hours without medical approval and supervision. So, unless you have that support from your healthcare provider, you should skip these types of fasting diets. Extended fasts aren’t necessary anyway — you can get the same results with shorter fasts (and less risk of pesky side effects)! Why make life harder for yourself?

2. The 5:2 diet

If you’re a fasting pro and prefer more of an off / on schedule, a 5:2 schedule could be a good fit. For five days of the week, you eat as you normally would. For the other two, you fast. And by “fast,” we don’t mean being completely food free (phew!). However, these two fasting days do involve hefty calorie restrictions (500–600 calories, or roughly 25% of your usual daily intake). 

Were you out at “calorie restriction”? Then this eating routine probably isn’t your fasting match, and you may want to move on.

Still on board, or at least cautiously curious? Think about your weekly schedule. You don’t want the fasting days back to back, so are there clear days that would be easier to plan around? 

You also want to factor in your health goals and personal preferences. One recent trial associated 5:2 with weight loss and improved weight management [7], but other studies show it may not be more effective than traditional calorie-counting routines.[8] You’ll also need extreme discipline on those fasting days — and you can’t necessarily go full bottomless-buckets-of-wings on non-fasting days, either. 

If you’re pretty confident in your fasting and meal-planning know-how, and the thought of a little moderation — and a little math — doesn’t sound too bad, 5:2 might be for you. However, while we believe a 5:2 diet may benefit some people, we don’t recommend it without approval by a healthcare professional; 500–600 calories is very low and may put your health at risk.

3. Alternate day fasting

Similar to the 5:2 approach but slightly more intense, an Alternate Day Fasting routine features alternating days of typical eating patterns and days of eating only 500–600 calories. Again, this fasting method is definitely not right for beginners, people who don’t like calorie counting, or people who prefer more low-key, consistent fasting. 

It’s also not safe for anyone with the “let’s wing it” meal planning style. (Absolutely no judgment here — we just want to ensure you’re set up to fuel that superhero body of yours, and last-minute grocery shopping when you’re starving or late-night orders from the nearby pizza shop aren’t usually conducive to nutrient-dense meals.)

There is a little bit more evidence that speaks to the benefits of this fasting approach (including weight loss and better heart health [9,10]), but equally, there are some studies that question its effectiveness.[11] 

Still, if you do better with on / off approaches and feel comfortable with a few days of significant calorie restriction, it’s one to consider. Just be sure to get the green light from your doctor since eating as little as 500–600 calories may put your health at risk. 

4. Eat stop eat

If you’ve mastered the on / off approach and want to step things up without more rules or routine changes, Eat Stop Eat may be an ideal challenge. 

This fasting method involves two non-consecutive 24-hour fasts per week. That doesn’t mean two individual days of not eating, though. It means two days where you have one meal before fasting for the next 24 hours. When you have that meal and what that meal is is entirely up to you: you’re the architect (and the caterer, the designer, and accountant … ) of this event. The rest of the time, you eat as you normally would. 

Even if you’re technically eating something every calendar day of the week, a 24-hour fast is no joke, and it can be difficult to meet your nutritional needs and stay safe, so our experts tend not to recommend it. There isn’t evidence to suggest it’s more effective than less restrictive fasting, either. So, if you’re considering this approach, speak to your healthcare provider and try it with their supervision. 

If you’re starting to feel overwhelmed by all these potential fasting plans, it’s probably a good time to mention you can always take our SIMPLE quiz to see which, if any, might work for you. With a few clicks, you’ll have access to a customized plan, a corner filled with expert support, and a community of other fasters who have been there, tried that. 

5. OMAD

The one meal a day diet (OMAD) is a routine involving — surprise — eating only one meal and fasting the rest of the day. And no, by “one meal,” we’re not talking about a leisurely four-hour feast with twelve courses situation: we mean one standard meal + fasting for about 23 hours every day. 

That equals serious effort when it comes to planning and preparation for meals and fasting windows.

This type of fasting approach is highly restrictive, especially compared to other plans that involve shorter fasting windows and some days off. While there are a couple small-scale, short-term studies that suggest eating one meal a day might lead to lower body mass or lower fat mass [12,13], again, there isn’t really evidence that “more” is “better” with fasting restrictions. Therefore, our experts strongly recommend trying other approaches first — and if you really want to give it a go, get your healthcare provider to review and safety-check your plan. 

6. Water fasting

Water fasting involves going 24–72 hours drinking only water and going completely without food. 

This process opens a whole can of worms around dehydration, low blood pressure, fatigue, headaches, mood changes, and other potential risks and side effects. Plus, while it may help you lose weight and may benefit health in some ways, it’s not a safe and sustainable fasting routine, and there isn’t evidence to suggest it’s more effective than other fasting approaches in achieving those potential health benefits. 

We don’t recommend this plan unless you have medical supervision. So, unless you’re working directly with your healthcare provider, strike this routine from your possibilities.

Hold on, what is intermittent fasting exactly?

Whew, okay, so there are a lot of different types of fasting. 

If your mind is spinning, you’re not alone. This stuff can be confusing, so that’s why we’re here to help.

Let’s quickly reduce it to the basics: intermittent fasting — regardless of the method — involves switching between periods of fasting and periods of eating on a regular schedule. 

Every different type of fasting requires different periods and timelines of eating and fasting, and some also involve calorie restrictions. However, whatever type of intermittent fasting you do, the fundamental concept is the same: for a defined period, you take a complete break from eating. 

No foods are completely off the table, either. It’s all about when not what you eat (though you still want to ensure your body gets all the nutritious power-ups it needs).

 Looking for some guidance on building fasting-friendly meal plans? Our experts have rounded up what to eat during intermittent fasting, what you can drink while fasting, and what breaks a fast to eliminate the guesswork. 

Still a bit overwhelmed? Read our guide on intermittent fasting for beginners.

How does intermittent fasting work? 

Right, now you get what intermittent fasting is, but how does it actually work? 

The concept of fasting actually goes back thousands of years, but we know you’re probably not here for a history lesson. 

Let’s hope you’re okay with a little biology, though, because we’re about to dive into the body to see where this particular type of eating routine got its inspo.

After you eat, your body gets to work on turning food into helpful body stuff, like energy, fat, muscle, and brain power. Once it spends a few hours digesting and distributing everything, it’s happy to chill in what’s called a post-absorptive state for the next 8–12 hours. 

After that internal R&R, your body then enters a fasted state (also known as “ketosis”). In this fasted state, your body is primed to burn fat instead of sugar to use as fuel. Think of it like dipping into your personal power reserves. 

On your average day, you likely won’t go long enough without eating to trigger this fasted state, so intermittent fasting is a straightforward way to initiate this natural body phase. Plus, having less time to eat generally equals less eating (there’s that calorie deficit!).  

How to choose an intermittent fasting schedule? 

So you think you can fast. And you want to. But what are the different types of fasting that will work for you? 

Choosing an intermittent fasting schedule is guided by one thing and one thing only: you. 

That’s right, you’re calling the shots here. When you’re considering if fasting is right for you, and if so, which fasting approaches might be best, you should factor in the following: 

• Your unique body and its nutritional needs. Do you become a hungry hulk if you skip breakfast? Does your immune system need extra support and daily nutrients? 
• Your fasting goals. What’s your endgame? Do you want to explore types of fasting for weight loss or another specific health goal, or are you looking to fast for easier meal planning? 
• Your schedule. Is it realistic to fast every day, or are there days when your eating routine needs to stay put? Are there any standing commitments or social events to work around?
• Your preferences. Do you prefer several meals or one big one? Do you like meal planning, or do you find it tedious? Do you like flexibility or a more consistent routine?
• Your lifestyle. Can you only eat dinner after eight once the kids are in bed? Are you a fan of intense morning cardio and need to have enough fuel available for a safe workout sesh?

Health risks and benefits of intermittent fasting 

Generally speaking, intermittent fasting is safe. 

However, we always recommend speaking with your healthcare provider before making any decisions that might impact your health. You should be particularly cautious if you: 

• Are pregnant, breastfeeding, or trying to conceive; 
• Have a history of or are currently diagnosed with disordered eating;
• Have a medical condition (like diabetes);
• Are under the age of 18, or 80 years old or more; or
• Are prescribed medication (for example, anti-hypertensives, diabetes medications, or any that need to be taken with food).

Even if you don’t identify with any of these categories, you may still experience intermittent fasting side effects. We know it’s frustrating not having crystal-clear insight into how your body may react to fasting, so we’ve rounded up the research to give you at least an idea of what to expect. 

Lower inflammation 

Inflammation contributes to many chronic and acute illnesses, like high blood pressure and heart disease. Some studies have linked intermittent fasting to reducing inflammation and inflammatory diseases.[14]

Lower risk of type 2 diabetes

Intermittent fasting can improve insulin sensitivity, reduce insulin resistance, and decrease both cholesterol and blood glucose levels for individuals living with overweight and obesity.[5,15,16]

A healthier heart

By lowering inflammation, cholesterol, blood sugar, and insulin resistance, intermittent fasting may also support our cardiovascular health and increase our heart’s resistance to possible pathogens.[17,18]

A healthier brain

Some studies suggest intermittent fasting can promote healthy brain aging and enhance circulating BDNF (a protein that plays an important role in the growth and survival of nerve cells), which may lead to an increase in BDNF in the brain, too.[19,20]

Metabolic changes

When we cut calories, our metabolism can slow down as a self-preservation mechanism. So, does intermittent fasting slow metabolism, too? Some research suggests fasting may introduce beneficial metabolic changes, like increasing your metabolic rate and your ability to oxidize fat [21,22,23], but some studies suggest the opposite.[24] Pairing fasting with strength training and lean protein can promote lean muscles and lower body fat percentages.[25]

Hormonal changes

Some research suggests that assigned-at-birth men and women may respond differently to intermittent fasting because it may decrease certain reproductive hormones while not affecting others.[26] A reduction in androgens (like testosterone) could be beneficial for women with polycystic ovarian syndrome but detrimental to men. However, existing research is very limited and fails to explore the effects of fasting specifically on trans men and women and individuals currently on hormone replacement therapy. 

Mood changes 

While some studies suggest intermittent fasting may reduce symptoms of anxiety and depression [27], others suggest it could increase negative emotions and decrease positive emotions.[28] While it’s not clear who may or may not benefit from fasting when it comes to mood, we do know it’s common to feel hungrier, crankier, or grouchier when you initially start fasting, but that shouldn’t last more than a week or two.

Decreased concentration

Your brain needs certain nutrients from food to function and perform cognitive processes.[29] Following a fasting-based food routine can lead to depriving your brain of these nutrients if you aren’t careful in planning your meals, and these deficits can lead to things like brain fog, headaches, and fatigue. 

Higher risk of disordered eating 

Intermittent fasting helps bring more conscious awareness to your eating habits and what you eat. While this mindful focus can be a helpful motivator for people looking to introduce more nutrient-dense foods into their routines, it can also lead to disordered relationships with food or exacerbate disordered eating tendencies.[30,31] That’s why we always emphasize fasting isn’t suitable for anyone with an eating disorder history.

Simple’s expert opinion and final thoughts 

The team here at Simple all agree: the best type of intermittent fasting is the one that’s right for your unique body — and one that you can stick to. When thinking through potential intermittent fasting plans, you want to ensure your needs, goals, schedule, preferences, and lifestyle are top of mind.  

While all intermittent fasting approaches can benefit overall health, everyone responds to fasting differently, and fasting may not be a good fit — or work — for you. There’s also not a “more is better” element: Shorter, less restrictive fasts may offer the same benefits as the more intense methods. 

Still not sure where to start? Head to our SIMPLE quiz today to learn more about which plan might work best for you and get tips on when and how to get started, stay motivated, and achieve your goals. We’re here to set you up for success, whatever that means for you. 

Frequently asked questions about the different types of intermittent fasting 

Which type of intermittent fasting is best? 

The type of intermittent fasting that’s best is the one that is best for you — that means it fits your body, goals, and preferences. For the best results, it should also be one you can sustain. Different types of fasting-based methods may hit differently, so you want to be guided by what suits your lifestyle.

What type of intermittent fasting is best for fat loss?

There’s no universal fit for what type of intermittent fasting is best for fat loss — results can depend on your unique circumstances, including things like your age, existing health conditions, levels of physical activity, and what foods you eat during eating windows.

Which type of intermittent fasting is best for weight loss?

Which type of intermittent fasting is best for weight loss is based on your individual characteristics and circumstances, though any fasting method can work for weight loss since it creates a calorie deficit. If you’re fasting to lose weight, speak with your healthcare provider (or take our quiz!) about different types of fasting for weight loss to see which one(s) might work best for you.

Is the 12:12 or 16:8 intermittent fasting better?

Again, whether the 12:12 of 16:8 intermittent fasting method is better depends entirely on you! With intermittent fasting, different types will have different impacts on different people, but our users have found success with both. To ensure you hit that fat-burning fasting state, though, the 16:8 approach is a better bet.

Which fasting method is most effective?

The most effective fasting method — and the one that is also safe and provides more lasting results — is the one that’s right for your unique body, and different types of fasting diets may impact it differently. If you’re not seeing the results you hoped for, we have a handy “intermittent fasting not working” troubleshooting guide. You can also review our rundown of common intermittent fasting mistakes.

Written by Aly Owen

Medically reviewed by Josie Porter, RD

Published on | Updated on May 3, 2024