20/4 Intermittent Fasting: Ultimate Guide To Warrior Diet

Intermittent fasting is one of the hottest trends within the low-carb community today.

Whether you’re trying to get into ketosis fast, keep the pounds coming off, or maintain your losses, switching from a general keto diet to one that includes an intermittent fasting schedule is often recommended.

Intermittent fasting first began when the Warrior Diet hit the market in 2002. 

Unlike other carbohydrate restriction programs at that time, it stressed the idea of timing when you eat, as well as what and how much.

The Warrior Diet, often referred to as 20:4 intermittent fasting, was about eating mostly in the evenings, using a 4-hour window.

You ate nothing before or after that 4-hour time slot.

More recently, a wide variety of intermittent fasting schedules have surfaced among keto dieters, with many of them far less strict than the original 20:4 protocol.

But none of the new kids on the block have been more effective than the original 20:4 Intermittent Fasting routine.

Additional choices have simply made fasting more accessible to a larger group of low-carb dieters.

Accessible is good, but does the 20:4 Intermittent Fasting protocol really work? And why would you want to include intermittent fasting in your low-carb weight-loss program?

Why Intermittent Fasting?

Keto is specifically designed to switch your metabolism from predominantly burning glucose for fuel to one that prefers to burn fatty acids and ketones.

This switch in metabolic pathways lowers your basal insulin level and curbs your appetite, so you find it easier to eat at a caloric deficit.

From the very first day that you reduce your calories and carbohydrates, the body seeks to bring itself back into energy balance.

If you only have a small amount of weight to lose, you should be able to make it to goal weight long before the body succeeds in doing that.

But if you have a large amount of excess body fat, the body might succeed in re-establishing equilibrium before you’re as thin as you want to be.

If that happens, you’ll experience a weight-loss stall or plateau that a standard ketogenic diet won’t be able to break through.

When the keto community first adopted intermittent fasting, there was a large group of dieters who had stopped losing weight on Atkins and other low-carb diets.

These dieters needed a painless and practical way to further cut calories without having to actually count them.

Other dieters were so severely insulin resistant to weight loss that they plateaued almost right away, shortly after going keto, and needed a metabolic fix to help them carve off the pounds.

Turning to intermittent fasting gave both types of dieters the help they needed to correct their hormonal imbalances and reduce their food intake enough to begin burning fat again.

If you’re struggling to lose weight on keto, switching to a 20:4 Intermittent Fasting regime might be able to get the scales moving downward again.

What is 20:4 Intermittent Fasting?

Unlike the Warrior Diet briefly described above, the 20:4 Intermittent Fasting protocol used by the low-carb community today alternates a lengthy fasting period with a traditional ketogenic diet.

The lengthy fast allows insulin to stay low for an extended period of time.

The “20” in the 20:4 formula means you go 20 hours without eating anything, including ketogenic foods.

All you can have is no-calorie liquids.

This isn’t as bad as it sounds because you’ll be sleeping for 8 of those 20 hours.

The 20 hour fast is called the fasting window.

The “4” in the 20:4 formula means you eat a normal keto diet during the four consecutive hours that you’re not fasting.

The 4 hour eating period is called the eating window.

The hours you eat is up to you.

You don’t have to limit your eating to just evenings, like in 2002. You can tailor your 20 hours of fasting and 4-hour eating window to fit your personal preferences, hunger level, and what’s going on in your life.

What Food to Eat During 20:4 Intermittent Fasting?

There has been a lot of research on fasting done over the years, but most of the work has been done on animals, and in particular — mice.

Unfortunately, research findings that apply to mice do not always correlate with humans, so most of the information that’s available on what to eat and drink for a successful fasting regime is highly subjective.

Standard rules for a 20:4 fast are to not eat or drink anything during the fasting hours that contain calories.

Some dieters strictly follow this rule, while others do not.

Out of all of the intermittent fasting options, a 20:4 plan is one of the strictest programs to go with, so not everyone has the capacity to stick with that 4-hour window, especially those who are used to enjoying a little double cream and sugar substitute in their coffee in the morning.

Many dieters will drink Bullet-Proof Coffee in the morning and then eat during their 4-hour window at night.

Others, are hungrier during the day and find it easier to schedule their eating during breakfast or lunch and then forego eating at night.

No matter which window frame you choose to use, or how many meals you choose to eat throughout that 4-hour period, the consensus on food is to stick with a very low-carb diet.

Some even choose to go zero carb.

A very low-carb diet is defined as less than 30 carbs a day, with most dieters tailoring their one or two meals to a maximum of 20 carbs, or less.

When you eat fewer carbs, hunger dramatically goes down, making it easier to get through those 20 hours of fasting.For this reason, it’s best to also stick to ketogenic basics:

  • meat, fish, poultry
  • eggs and cheese
  • leafy greens
  • very low-carb vegetables
  • spices without sugar
  • few low-carb condiments
  • simple low-carb sauces and gravies
  • bone broth to keep sodium up
  • water or sparkling water
  • coffee or tea

However, since your meals will be greatly compacted on a 20:4 schedule, you might have to make higher protein choices that provide less fat to make it work best.

This is particularly true if you’re trying to fulfill your protein needs within a single meal.

To do this, choose chicken or turkey breast, pork loin, tuna, or beef loin cuts more often.

Most keto dieters have better success when spacing out their protein intake throughout the entire 4-hour space. This allows them to eat fattier cuts of meat.

Snacking during that 4-hour window is absolutely fine.

In fact, many people prefer to eat one hearty meal at the beginning of the window and one snack just before the close of the eating period.

What you don’t want to do is schedule your eating so close to bed time that you’re uncomfortably full.

Don’t stuff yourself. Intermittent fasting isn’t mean to be painful. Plan your meal early enough in the evening that you can get a good night’s sleep.

If you go over your eating window slightly, try not to stress about it. There will be days when you go way under those 4 hours.

What matters most is the consistency of the pattern you’re establishing.

At the same time, if it comes down to snacking outside that 4-hour window or quitting your keto diet, go with the snack.

Having a 16:8 or 18:6 day now and then isn’t failure.

Since fasting can be difficult for many people, you might find it easier to ease into a 20:4 routine by gently shortening the window each week.

It’s not always workable to go straight to intermittent fasting if you’re a keto beginner. Fasting is less stressful and easier to succeed with if you’re already in ketosis and learn to gradually eat less food.

What Happens During 20:4 Intermittent Fasting?

If you are not in ketosis, intermittent fasting will get you there pretty quick. S

ince you aren’t eating anything for 20 hours, and only ketogenic foods during your feeding window, your body will be forced to use up its glycogen stores, the storage form of carbohydrate.

If you are already in ketosis, what happens during fasting depends on how full your glycogen stores are.

If partially full, the liver will use that first before dipping into your fat stores. This will ensure that you get into an optimal level of ketosis.

If glycogen is already depleted, the body will simply start to burn more body fat throughout the fasting window.

The longer you go without eating, the lower your insulin level stays, and the longer your liver will be able to mobilize and utilize your body fat for fuel.

While this is what a ketogenic diet is already designed to do, provided you stay beneath your carbohydrate tolerance level, going for extended periods without eating guarantees that you’ll be burning body fat as long as possible.

Ordinarily, low insulin signals the liver to dump its glycogen stores into the bloodstream because very low insulin levels means your blood glucose is too low.

But if you’re doing 20:4 intermittent fasting, your glycogen stores will be too low to use.

The lack of liver glycogen forces the liver to either use amino acids for glucose, called gluconeogenesis, or dip into your body fat stores to make up for the lack of fuel. 

Dipping into your fat stores for a longer period of time each day will also result in a higher blood-ketone level, making it more likely that you’ll stay in the optimal zone for ketosis.

20:4 Intermittent Fasting VS Other Fasting (e.g. 16:8)

When intermittent fasting was first adopted by the keto community, a 19:5 ratio was pretty common.

Today, the most popular intermittent fasting routine is a 16:8 because it’s not as difficult to follow as 20:4, but many keto dieters are using the 20:4 schedule and getting great results.

The first number in these ratios always indicates the amount of time you spend fasting during the day, while the second number indicates the number of hours you can eat each day.

However, this can get confusing because some fasting programs use similar numbers, but they mean a very different thing.

For example a 5:2 Intermittent Fasting program has you fast for two complete days out of the week (a 24 hour fast for each of those two days) and recommends that you eat a standard keto diet for the other five days.

Which type of regime is best for you depends on your hunger level and how insulin resistant you are.

The more often you eat throughout the day, the more insulin you’ll secrete in response to the glucose that food provides.

If you’re on a ketogenic 16:8 regime, where you’re fasting for 16 hours throughout the day and eating during an 8 hour window, you’re going to be eating twice as long as on a 20:4 plan, so your basal insulin level will be a bit higher.

This isn’t necessarily bad.

How low you need your insulin to fall depends on your ability to access and utilize body fat.

Some people’s insulin levels can drop too low with extended fasting routines, so a 16:8 program works better for them. They need the larger window to optimize their basal insulin level.

The trick is to find the schedule that will allow your insulin to fall low enough to lose body fat, comfortably, but not so low that you get so hungry that you cheat.

Benefits and Side Effects

Weight loss and lower insulin levels are not the only benefits to adding a 20:4 Intermittent Fasting schedule to your keto diet. Other benefits include:

  • increase energy
  • lack of hunger and cravings
  • improvement of blood glucose levels
  • better mental clarity
  • improved concentration
  • reduced inflammation
  • lower cholesterol numbers
  • activation of cellular cleansing (autophagy)
  • lower insulin secretion in response to protein

Basically, any condition that is improved by lowering your insulin level will see a major improvement when switching to intermittent fasting. Plus, if you were overeating carbs before, you’ll see a dramatic dip in your hunger and cravings.

In addition, since intermittent fasting enables insulin levels to remain low for an extended period of time, using this eating pattern can also prevent insulin resistance from forming or correct minor cases of insulin resistance without any further intervention.

According to Dr. Jason Fung, a diabetes specialist, severe insulin resistance like Type 2 Diabetes would need a much longer fasting period than what a typical intermittent fasting regime provides.

Maybe, a full 24 hours or even several days to see improvement. 

However, a consistent 20:4 program still provides enough benefits to make intermittent fasting a viable option, even for diabetics.

Does it Work?

By reducing your food intake to one or two meals a day, you’ll lower your insulin levels and make your fat stores more accessible to the liver.

However, you still have to consume fewer calories than you were eating before, or increase your activity, to break through a weight-loss stall or plateau.

If you overcompensate for the lack of calories by overeating a day or two down the road, or resting more than usual, fasting won’t do you much good.

The idea is to upset the body’s energy balance.

The only exception to this would be if you have unusually high insulin levels that are interfering with fat loss on a standard keto diet and causing your weight loss to stall.

Correcting high insulin, in that case, would result in weight loss without having to cut food intake.

Overall, intermittent fasting comes with a huge success rate, due to its structure. Insulin stays low for a longer period of time, giving the liver more space to burn body fat.

It also makes it easy to take in less food and provides benefits to your body’s cells, as well.

In one human study, Mark Mattson, the senior investigator for the National Institute on Aging, and his colleagues looked at the effects of intermittent fasting on:

  • weight loss
  • breast cancer
  • diabetes
  • and cardiovascular disease

Among the young overweight women who participated in that study, intermittent fasting was found to be just as effective as a low-calorie diet for weight loss.

It improved their insulin sensitivity, as well as other biomarkers.

Like all weight-loss and health-improvement diets, however, compliance is absolutely essential for the diet to work.

But when it comes to fasting, the length of time needed to see results will vary from individual to individual.

What are Some Alternatives?

Give yourself permission to experiment with the different fasting techniques before committing to a single plan.

There’s no failure in shopping around to find the best fasting program that fits your lifestyle and metabolism.

Also, be willing to juggle that 4-hour window to various times of the day to see if morning, afternoon, or early evening works best before you come to any conclusions about the viability of using a fasting protocol.

Be flexible.

Don’t avoid going out with your family or friends just because you’re fasting. Feel free to move your hours to the best time period for that event, and then go back to your normal schedule the following day.

Also, keep in mind that the numbers are not set in stone.

You can change the numbers to be anything you like.

Try an 18:6, 17:7, or 19:5 if those numbers work better for you. You don’t have to do what’s popular.

If you don’t want to worry about the right time to eat, you can also choose to eat one or two meals a day and forgot about how long it takes to eat.

Some people eat one meal a day in the evening and then a snack in the early afternoon only when needed.

Others drink coffee in the morning, with cream and sugar substitute, and then don’t eat until they’re physically hungry much later in the day.

Tailor the plan to fit your own style and preferences.

A 4-hour window doesn’t mean you have to eat for 4 hours, or even at the start and end of the period. It’s only a guideline to help you control your insulin level.

If a 2 hour window is more comfortable for you, then adopt a 22:2 schedule.

Another alternative is fasting for 24 hours once or twice a week and eating keto on the other days.

Many find 24-hour fasting to be more effective and doable than fasting for only part of the day. Fasting increases the time spent using energy that’s already stored, and for some people, a 24-hour fast is just easier to stick to.

Final Thoughts

It really doesn’t matter how you do it.

Society has convinced us that we need to eat frequently throughout the day to be healthy, and that just isn’t true. If you’re overweight or obese, you’re eating too much for your body and lifestyle, no matter how much, or how little, that is.

Corrections do not have to be as harsh as intermittent fasting. Sometimes, just getting up from your desk and moving more throughout the day is enough.

But if you’ve stalled partway to your weight-loss goal, you do need to pick an alternative to what you’re already doing. Many people do great on lower fat keto diets, especially those who have sit-down jobs.

While high-fat is typical, it certainly is not mandatory for health.

The best approach to weight loss is to make one small change at a time and then evaluate the results.

31 thoughts on “20/4 Intermittent Fasting: Ultimate Guide To Warrior Diet”

  1. The 20:4 is much more effective than the 16:8 for me. I’m up and down in weight a lot and I noticed results in my clothes within 3 days with the 20:4 without having to workout while it took a week and a half of 16:8 with exercise to achieve similar level of results.

    1. I found much easier to go 20:4 since I don’t have to bother eating during the 20 hrs fasting window. I noticed if I eat in a 16:8 pattern I tend to eat more since it triggers hunger the moment I start ingesting food and will remain eating for the rest of the day. That does not happen in 20:4 regimen, which I usually begin eating in the evening.

  2. Angela Wybourne

    I get home from my physical job about five. I usually have a snack – eggs on toast or a cheese salad sandwich before I prepare dinner – lots of veges and chicken fish or beef – the only starchy vege being pumpkin. Then if I’m still hungry, maybe some fruit with a piece of cheese. I’ve chosen this lifestyle for the aging benefits (I’m 53) & I’ve found it works really well. In fact I started doing it before I realised IF was a thing. I found my energy remained higher & more constant at work when I didn’t eat than when I did. I want to eat like this for the rest of my life. 🍗🥦🥒🌶️🥩🥝🍓🥑🧀

    1. Hello, I’m 52 and started Keto about 5 mos ago. I’m currently playing with IF. I just heard, Thomas DeLauer say that people over 40 should do the 20/4 every other day. If doing IF every day, out metabolism slows down. I did my first 20/4 today. I had been doing 16/8 or 18/6. Just curious. Thanks.

    2. Michelle Merchant

      Thank you so much for the very thorough explanation! I was feeling confused about the judge variety of preferences the “experts” suggest. After 2 weeks on 20/4 at age 65 I am already feeling good and beginning to see the benefits. I am feeling strong enough to gradually increase exercise from a pretty sedentary “retirement” norm.

  3. I work a physical job (move furniture) that requires walking 8 miles per day. I also started the 20/4. I tended to overeat on the 16/8 schedule.

  4. Great article! My peak weight (285lbs I’m 6’4″ so I could hide it pretty well) was in February of 2017 which I realized after looking at pictures from a recent trip to Mexico! I couldn’t believe that was me in the photos. I immediately started researching Bob Briggs (Butter makes your pants fall off) which kick my program off. Dr. Jason Fung’s book on Fasting has become my go to book when I need a refresher. Current weight is 196, waist 34 from 42, XXL to Medium. Blood pressure from 145/100 to 110/70. Total Cholesterol 178. IF has been a game changer and completely transformative.


    1. Great results Norman. I am curious were you taking medication to control your blood pressure prior to such impressive number reductions?


  5. Hi im doing 20/4 fasting. How much weight I can lost as now I’m 78kg my height is 174cm.how long I should to get the best results.


  6. I have lost 115 lbs on 20:4 schedule. I’m 61 years old and have been obese for the past 20 years. I was on diabetes medication, blood pressure meds, high triglyceride meds and now I have normal numbers and am off all meds. I feel great, have good mental clarity, and don’t need as much sleep. This is definitely a lifestyle change that is easy for me.

    1. Thank you. I started the diet 10 days ago, I am 63 years old. have been checking my blood pressure for a longtime; always at around 145/100. How long does it take to go down? Thank you, you inspire me. Bernard

  7. What a fantastic and informative article, thank you. I have been trying a Keto diet for some time and have experienced a plateau of sorts (although have kept on Keto as I actually enjoy it). Did my first 16:8 fast yesterday and the scales went down a bit! Trying the 20:4 today as I was full after meal number 2 and can’t see that I will want to eat before bedtime now (well, let’s hope not!). So – experimenting with IF but so far so good. Many thanks.

  8. I just started 20/4 yesterday and I already fell fantastic. The scale has already gone down 2 pounds and I am not hungry like I thought I would be. Does everyone do 20/4 everyday? Or is it better to do it every other day?

  9. One thing I haven’t figured out is how to come up with a “calorie plan”. I’ve been doing a 16:8 if for around 2 months now and Basically I just make sure I’m “satisfied” with my food intake.
    I would find it helpful if I could have a more concrete idea of the actual amount of energy I should be putting into my body.
    Great article. Everything makes sense to me but I’m feeling like i’m a little stalled out on the calorie thing. 🙂

  10. I’ve been doing 20:4 during the week and more relaxed over the weekends with 16:8. The 20:4 mostly become 22:2 or even 23:1 and I’ve been doing this for 3 weeks now. I have had no side effects at all, clearer mind and feeling much better for it. Increasing Yoga in the mornings and making sure I’m taking vitamins etc.

  11. very informative.thank you very much i really have been struggling with my weight,iv been inspired and l’m going to start my journey tomorrow.

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