How to Intermittent Fast and Which Type of Fasting Is Right For You

Intermittent fasting has taken the world by storm. No longer is it the province of fitness freaks. No longer do you get weird looks because you skipped the break room donuts. Now you’ve got grandmothers trying it and doctors recommending it. It’s here, the benefits are legion, and you’re interested. But how should you do it? Are there different types of intermittent fasting? Are there different benefits associated with the various flavors of IF?

Thinking about fasting, reading about fasting, and reciting the benefits of fasting are all pointless if you don’t know how to go about doing it.

First, the most fundamental concept central to all the flavors of intermittent fasting is not eating. Skipping meals, skipping entire days of meals, letting yourself get a little hungry. There’s no getting around that. It will happen. let’s go over the different variations of fasting. I’ll give a quick rundown. Each involves not eating for a period of time, unsurprisingly.

A couple other rules that apply to all the given methods:

1. Sleeping hours (provided you don’t sleep-eat) count as fasting hours.
2. Eat well regardless. While some fasting plans tout their adherents’ ability to eat crappy food and still lose weight, I’m not interested in fasting solely as a weight loss method. Keep your food Primal as possible.

Okay, on to the variations.

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12:12, 16:8, 18:6, or 20:4 Intermittent Fasting

As the names suggest, these breakdowns of intermittent fasting involves fasting for either 12, 16, 18, or 20 hours and taking in all of your food for the day over the remaining window of hours.

How to find out which fasting length is the the best one for you? There’s only one way. You have to experiment.

You can start with a 12:12 intermittent fast, which comes with the benefits of intermittent fasting and is easy to do for most people. You stop eating a couple of hours before bedtime, and delay breakfast a couple of hours after waking. If that works well, extend your fasting period the next day, and repeat until you find the eating and fasting pattern that feels good.

Lots of diets have added more detail to the intermittent fasting model, but bare-bones intermittent fasting is simply a shorter feeding period.

If you’ve heard of Leangains, Martin Berkhan’s incredibly popular fasting protocol, you’ve heard of 16:8 intermittent fasting. How does it work?

1. A daily 16 hour fast during which you eat nothing containing calories. Coffee, tea, and other non-caloric fluids are fine. Some people get away with a little cream in their drink.
2. A daily 8 hour eating window.
3. Three days of weight training, ideally performed at the tail end of the fasting period. To improve performance and muscle protein synthesis, you have the option of consuming 10 grams of branched chain amino acids 10 minutes before the workout.
4. Always eat high protein.
5. On training days, eat more carbs and less fat.
6. On rest days, eat more fat, fewer carbs, and slightly reduce calories.
7. Most people begin their fast after dinner (say, 9 PM), workout in the afternoon (at around 12 PM), and break their fast immediately post-workout (at around 1 PM), but you can use any schedule you prefer as long as you hit the 16 hours of fasting.
8. Your post-workout meal should have about 50% of your day’s caloric allotment (a real feast).

Who should try it?

12 or 16 hours isn’t a long time to wait for a meal, which makes intermittent fasting a great model for anyone who wants to experiment with fasting. One benefit of fasting this way is that it’s not that long a fast – you eat every day. It is totally doable. Whether you add the detailed lifting days and carb days is up to you.

Women may have better success with slightly shorter fasting windows—12-14 hours long instead of 16 hours. To understand why, check out my post on women and fasting.

People with steady eating schedules will have more success than people with erratic schedules. A huge benefit of intermittent fasting is the hormonal entrainment induced by regular feeding times. Once you get locked into your routine, your hunger hormones will adapt to the schedule, and the fasting should get easier, or even effortless. For this reason, it’s a good idea to get a feeding schedule and stick to it.

OMAD — One Meal a Day

Ori Hofmekler’s plan is based on the feast-and-fast concept:

1. Eat one meal a day, at night, and make it a big one. A real feast. You have three or four hours to eat until full. So it’s basically 20/4 hours.
2. You can occasionally snack on low-calorie raw fruit and vegetables during the day, but try to limit protein as much as possible until the feast.
3. Exercise during the day, in a fasted state.

Who should try it?

People who have trouble sticking to a stricter fast will do better on the OMAD, as it allows light eating during the time leading up to the feast, but I wonder if you’d be squandering some of the benefits by eating.

Alternate Day Fasting

Researchers often use this method in lab studies:

1. Eat normally one day (last meal at, say, 9 PM Monday).
2. Don’t eat the next day.
3. Resume eating the day after that (at, say, 9 AM Wednesday).
4. It works out to a 36-ish hour fast, although there’s plenty of wiggle room. You could eat at 10 PM Monday and break the fast at 6 AM Wednesday for a “mere” 32 hour fast.

Who should try it?

People who have no trouble going to bed hungry. With other intermittent fasting methods, you can always manage to get to bed with a full belly; with ADF, you will be going to bed on an empty stomach several times a week. That can be tough.

That said, the therapeutic benefits to serious conditions will most likely really be pronounced with this way of fasting. The casual 20-something Primal eater who lifts heavy things and enjoys going out with friends? Probably not ideal. The older Primal eater interested in generating some autophagy and maybe staving off neurodegeneration? It might just work out. And while I’m not able to tell a cancer patient undergoing chemotherapy what to do, I’d guess that the longer fasts will be more beneficial in that regard, too.

Eat Stop Eat

Put together by Brad Pilon, Eat Stop Eat is really basic:

1. Once or twice a week, don’t eat for 24 hours.
2. Start your fast in the morning, at lunch, or at dinner. It doesn’t matter as long as you don’t eat for 24 hours.
3. Break your fast with a “normal-sized meal.” Don’t try to make up for the lost calories by feasting.
4. Exercise regularly.

Who should try it?

People interesting in fasting for the therapeutic benefits (cancer protection, autophagy, life extension, etc.) would probably get a lot out of this method, as opposed to people interested in the body composition benefits.

Going a full 24 hours without food is a much tougher slog than going for 16 hours. In my experience, going lower-carb and higher-fat makes longer fasts easier, so I’d have to say a low-carb Primal eater would do better than most.

But my personal favorite way of implementing fasting?

WHEN — When Hunger Ensues Naturally

I’m not going to put any bullet points here, because none are required. Instead, I’ll give a few scenarios:

I wake up bright and early on a Saturday morning. It’s about 65 degrees, the sun’s out, my dog is walking around with the leash in his mouth, and Red Rock Canyon is kinda calling my name. I’ve got my coffee already and I’m actually not all that hungry from dinner. You know what? I’ll go on that hike, skip breakfast, and really work up an appetite for lunch. Or not. If I’m hungry afterwards, I’ll eat. It’s a fast, but not really.

I hit the gym, put in a light workout, then swing by the beach for some sand sprints. I’m toast by the end and have to stagger back to my car, but I’m not hungry. Even when I get home and smell the grilled salmon, I have no desire for it. I might eat later that night, but only if my appetite returns. I’m fasting post-workout only because it doesn’t occur to me to eat, not because I’m following a plan.

I’m away on business, stuck on a layover that’s turned into a delay that’s turned into an overnighter. The only food available is a Kudos candy bar – I mean, healthy granola bar (they seriously still make these?) from the mini fridge, a greasy pizza joint on the corner across the street from the hotel, a Chinese takeout place next to the pizza joint, and a slew of fast food restaurants some ways down the road. It’s late, I’m tired, I had a Big Ass Salad before I left for LAX… you know what? I’m just going to skip the “meal.” I’ll figure out something at the airport in the morning (20 hour fast) or once I land (24 hour fast). And I’ll be okay either way.

That’s eating When Hunger Ensues Naturally.

This is the most natural, most effortless way of “fasting,” at least for me, because it allows a person to eat intuitively. Although most people will eventually acclimate to more regimented fasting schedules, and many may even need and thrive with that structure, I prefer a more fractal, loose, random pattern of “missing” (in quotations because I don’t feel like I’m missing anything, and that’s the whole point!) meals. I have no data on whether it’s as effective or more effective than the more popular methods, but I do know that I’ll often fast for 16 hours and eat for eight, or skip an entire day of eating, or sometimes (but very, very rarely) even approach a full 30 hours, and it seems likely that this random pattern of eating characterized the eating “schedules” of our ancestors.

In short, we’re all doing the same thing, chasing the same goals. We’re all skipping meals, reducing calories, staying active, and all the while we’re doing this without feeling miserable and restricted. It just so happens that because we’re efficient Primal fat-burning beasts, switching over to burning our own body fat reserves for energy during a fast is a natural, seamless transition. We often don’t even notice it. There’s no effort involved.

That’s the key: lack of stress. If any or all of these fasting methods stress you out, make you irritable, kill your performance, make you feel restricted, or reduce your ability to enjoy life, and these feelings persist beyond the first five fasts you attempt (when some adaptation difficulties are totally expected), you shouldn’t employ them. You should shelve fasting for a while and come back to it later, or never. It’s not a “requirement” or anything. It’s just a tool you can wield if your situation warrants it. In fact, this is the perfect opportunity to conduct an informal experiment of one. Try one style for a week or two, then throw in a a different style once or twice a week for a bit, then try another method. Compare and contrast. How did you feel? How did you perform at work, at home, and in the gym? Take some waist measurements perhaps, or analyze your favorite barometer of body composition to see how the different fasting methods worked – or didn’t work – for you.

Now, I’d like to hear from you. What’s your favorite fasting method? Do you have one, or you just kinda go with the flow? Be sure to review the previous installments below and if you have any questions about any of the stuff I’ve covered in this series, leave them in the comment section and I’ll try to get them answered for you next week. Thanks for reading!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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