Choosing an intermittent fasting (IF) schedule should be easy. Just pick the protocol with the most science behind it, right?
Another problem is that longer intermittent fasts don’t work for everyone. One meal a day might work for some people, but others find it stressful and draining.
Some of the more well-known IF protocols include overnight fasting, 16/8, OMAD, 5:2, and alternate-day fasting. If this is unfamiliar jargon, don’t worry! We’ll address these methods in more detail later in the article.
This article will help you find your optimal protocol of fasting and feeding, so you can settle into a sustainable routine.
Intermittent Fasting Defined
Intermittent fasting can be defined as temporary calorie restriction. When you practice IF, you limit your calories for a certain number of hours every day or for a certain number of days every week.
As a general rule, intermittent fasts start at 12 hours and end at around 36 hours of fasting. Any fast beyond 36 hours (up to 48 hours) is typically considered an extended fast.
(Learn more about intermittent fasting — including sample meal plans and tips for success — in this ultimate guide.)
An intermittent fast needn’t be a zero-calorie fast. Certain protocols allow for limited calories during feeding windows and still appear to help with obesity and other heart disease risk factors.[*] [*]
Hominids have practiced fasting since we began stalking the Earth millions of years ago. Back in prehistoric times, Grubhub delivery wasn’t a thing. (Unless you count someone dragging a carcass from cave to cave). If the hunt failed and the bush was bare of berries, you simply went without food.
We evolved, in other words, to oscillate between periods of fasting and feeding. When we fast, we can burn fat and activate cellular repair processes like autophagy.[*] When we feed, we can rebuild, grow, and heal.
Both are important, but today humanity is stuck in feeding mode. This is contributing to the obesity and diabetes epidemics that we are witnessing across the Western world.
The widespread adoption of intermittent fasting could help reverse this trend.[*] Let’s see what’s on the fasting menu.
Types of Intermittent Fasting
In the scientific literature, you will find five main types of intermittent fasting. These different methods cover both daily and weekly fasting routine options. Let’s review them.
- 12/12. This is your standard overnight fast in which you stop eating after dinner and resume twelve hours later at breakfast.
Good for: Beginners, easing yourself into a fasting schedule and those trying to maintain balance in work/family life.
Not so good for: Those who are prone to overeating and snacking. There may be a temptation to over feed in your 12-hour window.
- 16/8. When you practice 16/8, you consume all of your daily calories in an eight-hour window. This is commonly achieved by ceasing to eat after your evening meal, skipping breakfast the following morning, and then breaking the fast at lunchtime.
Good for: Those who have established a 12/12 routine and would like to experiment further with IF or are experiencing weight loss plateaus.
Not so good for: Those who struggle with morning hunger and fatigue.
- OMAD. OMAD stands for one meal a day. In this approach, you spend 23 hours fasting and consume all your calories for the day within a one-hour window. A similar method is The Warrior Diet, in which fasting lasts for 20 hours, allowing 4 hours for feeding.
Good for: Simplicity and productivity.
Not so good for: Beginners. Some may also find it hard to obtain the right balance of nutrients and calories in their one daily meal.
- 5:2. When you practice 5:2, you consume 0-25% of your normal calories two non-consecutive days per week. The other five days you eat normally.
Good for: Reaping the potential health benefits of IF, while only adjusting your schedule two days a week.
Not so good for: Those who struggle with hunger as portions will be drastically reduced on fasting days.
- ADF. ADF stands for alternate-day fasting. On an ADF regimen, you consume 0-25% of your normal calories every other day.
Good for: Those who have some IF experience and are looking to experiment with their routine.
Not so good for: Beginners and those who struggle with hunger and fatigue.
How to intermittent fast
If you’re a fasting veteran, feel free to skip this section. But if you’re new to fasting (or know someone who is), the next few paragraphs could save you a lot of stress.
Like exercise, fasting is a stressor. Would you try and run a marathon without working up to it? Of course not. The race would bury you.
The same principle applies to fasting. For anyone not accustomed to this style of eating, a 36, 24, or even 16-hour fast can feel intense and overwhelming.
The solution is simple: Start slow. Start with a 12-hour overnight fast, then work your way up one hour at a time.
Almost everyone can tolerate (and benefit from) an overnight fast. It’s a quick moral victory and an excellent way to prime your fat-burning machinery.
Fasting overnight can also improve your 24-hour wake-sleep cycle (the circadian rhythm), which in turn can positively influence numerous aspects of health.[*]
Okay, so you’re starting slow. Now what?
3 Criteria for Choosing an Intermittent Fasting Schedule
Choosing the right fasting protocol means doing what’s best for you. Here are three criteria to consider:
Intermittent fasting shouldn’t be a struggle. You should be relatively comfortable during your fasts.
This doesn’t mean you won’t get hungry. Hunger is inevitable.
But if the discomfort goes beyond hunger, you may want to pause and reconsider. Here are some signs your fasting protocol may need adjusting:
- You’re not sleeping well
- You’re in a bad mood during fasting periods
- Your exercise performance is declining
- You feel weak, tired, or stressed
- You resent family and friends for eating in front of you
If you’re experiencing one or more of these signs, consider backing off to a shorter fast. Your comfort and health are worth it.
How you fast also depends on your schedule. If your family has a sacred dinner ritual, alternate-day fasting might not be for you. Family time may take precedence.
As a rule, fasting frees up your schedule though. When you don’t have to worry about meal prep or eating, you can fill those blocks with other things.
For example, many people skip breakfast as a productivity hack. When the clock finally hits mealtime, food becomes a reward for a job well done.
#3: Health goals
Are you fasting to lose weight? To stay lean and strong? Or to reap other health benefits?
Get clear on this reason before settling on a fasting regimen.
If you want to lose weight, the longer regimens are probably more effective. The smaller your feeding window is, the fewer calories you’ll consume.
But keep in mind criteria #1, ease. If you’re perpetually uncomfortable while fasting, you probably won’t stick with the schedule.
It is also important to note that longer fasts are not ideal for maintaining or gaining muscle. The potential for calorie and protein restriction is too high.
Multiple studies, however, have found that people can maintain muscle on a 16/8 regimen while resistance training.[*][*] Sixteen hours may be a good upper limit if strength gains and muscle maintenance are your goals.
Calibrating Your Fasting Protocol
The smart way to calibrate your fasting protocol is by easing into it. Start with a 12 hour fast and scale up from there until you find a program that works best for your body.
Here’s how that might look schedule-wise on a week-by-week basis.:
- 1 week of 12-hour fasting
- 3 days of 13-hour fasting
- 3 days of 14-hour fasting
- 3 days of 16-hour fasting
- 3 days of 18-hour fasting
- Once you have established which IF protocol works best for you, you can then maintain this level, listen to your body, and adjust if needed.
If you experience discomfort at any level, drop back down to a more sustainable routine.
Remember that the goal isn’t to fast as long as possible or shed pounds as quickly as you can. The aim is to find a sustainable intermittent fasting schedule that suits your lifestyle and individual health needs. To keep things simple, you can use a diet tracker app like Carb Manager to help implement and maintain your custom intermittent fasting program . This way, you can record all your essential health metrics in one place. Once you have established your routine, you can sit back and reap the rewards of your progress.
Choosing a Fasting Schedule: FAQs
What Can I Eat?
You need to eat healthy and nourishing foods during your feeding window. Even if you’re on a limited-calorie fast, choose nutritious whole foods to maximize the benefits of your program. Also, low-carb and Ketogenic diets may be synergistic when combined with an IF schedule for general health and managing type 2 diabetes.[*]
What Can I Drink?
Hydration is also key when it comes to fasting. Not only does water maintain crucial bodily functions, but it can also effectively curb hunger pangs. If you wish to add a flavor to your fasting routine, black coffee, tea, and other zero-calorie drinks are all fair game. You’ll have to pass on the alcohol though.
Can I Take Supplements/Medication?
You may also be wondering about supplements and medication on your IF schedule. In some instances, it is recommended that these are taken with food, in which case you can include these within your feeding window. If you have any doubts about taking either during a period of fasting, we recommend consulting with your health professional.
Is fasting different for women?
Both men and women have been fasting successfully throughout human history. Some research, however, suggests small differences in how women fast. For instance, in one study, men had better muscular adaptations to exercise in a fasted state, while women did better in a fed state.[*] Another study found that a two-day-fast (longer than any intermittent fast suggested here) provoked a significant stress response in overweight women.[*] This hasn’t been shown in men.
Also, pregnant women and nursing women should be careful with fasting. There are too many important nutrients to pass along to the baby.
Is fasting suitable for everyone?
Most everyone can benefit from an overnight fast, but certain groups should be careful with longer fasts. These groups include pregnant and nursing women, underweight people, growing children, those with medical conditions (people with diabetes should have medical supervision), and those with eating disorders.
Will I lose muscle when fasting?
Assuming you consume adequate calories (especially protein) and also strength train, you should be able to maintain muscle while fasting. That’s what the research suggests.[*]
How do I manage my hunger?
Some hunger is inevitable during a fast, but it should stabilize and trend down as you adapt to your fasting regimen. Eating Keto during feeding windows also helps you adapt to using body fat for energy and smooths out your cravings. It also helps to consume non-caloric beverages like coffee, tea, and bone broth during your fast.
Isn't skipping breakfast bad for you?
Skipping breakfast, the literature suggests, may be a good weight loss strategy.[*] But other evidence found that women who skip breakfast had higher levels of cortisol, the stress hormone.[*] Some people do better with breakfast, some don’t. You’ll have to experiment to see what works for you.
Please note that as with any significant diet or lifestyle change, we recommend working alongside a registered health professional, especially if you are currently on any prescribed medications. Fasting is not appropriate for everyone and should be avoided by those with a history of eating disorders, pregnant and breastfeeding women, and anyone under 18.