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Intermittent Fasting on a Keto Diet

Intermittent Fasting on a Keto Diet


Intermittent Fasting, or “IF”, is a relatively new craze that is used as a supplement to your diet. It revolves around the timing of your food intake, and can have some benefits in the long run. There are quite a few people misinformed on fasting, so we’ll clear that up and explain how intermittent fasting can be useful.

I want to be clear that intermittent fasting should be used for CONVENIENCE only, not for better weight loss results. There are no studies on intermittent fasting that show clear weight loss benefits, but there are studies that show health benefits. We’ll get into those later. The thing that matters the most is HITTING YOUR MACROS. If you need to learn how to calculate your macros, visit our Keto Calculator.

Restricting yourself even more than you are is pointless – it’s not worth it if it makes you unhappy. Most people are fasting because of the few health benefits and the major convenience it has for their schedules. It has been reported (no studies backing it up) that it can help you if you are in a plateu – and I am talking about a plateu of 3 weeks or longer.

There’s 2 basic terms we need to understand here: feeding, and fasting. You’re in a feeding state when you are eating your food (naturally), and you are in a fasting state when you are between your meals.

The Approach

There are a few approaches when it comes to intermittent fasting.

  • Skipped meals. This is when you skip over a meal to induce extra time of fasting. Usually people choose breakfast, but others prefer to skip lunch.
  • Eating windows. Usually this condenses your entire macronutrient intake between a 4 and 7 hour window. The rest of the time you are in a fasting state.
  • 24-48 hour cleanse. This is where you go into extended fasting periods, and do not eat for 1-2 days.
Skipping breakfast with fasting

I don’t recommend that you go straight for a 1-2 day fast, but begin by restricting yourself to certain eating windows. Typically people restrict themselves to the hours of 5pm – 11pm. People often refer to their fasting windows by numbers: 19/5 or 21/3, for example, means 19 hours of fasting and 5 hours eating or 21 hours fasting and 3 hours eating, respectively.

Once you have the hang of eating on a schedule, you can try short periods of 18-24 hour fasting. Then you can judge if intermittent fasting is for you.

Whether you decide to do it every day, once a week, or twice a week is up to you – do what makes you feel best and listen to your body.

How does it work?

Fasting can help with overeating and calorie counting
The whole point of intermittent fasting is to allow ourselves to increase the amount of food we can intake at one time. Our bodies naturally can only take in a certain amount of food at once, so we are creating a sort of limit on our calorie intake.

This is also a great method for people that overeat. I tend to see people that forget to count the snacks that they have throughout the day, and wonder why they are putting weight on.

Your body will adjust itself to fasting, and you will find yourself not as hungry as you used to be. This allows you to properly record and maintain their nutrient intakes.

In this fasting state, our bodies can break down extra fat that’s stored for the energy it needs. When we’re in ketosis, our body already mimics a fasting state, being that we have little to no glucose in our bloodstream, so we use the fats in our bodies as energy.

Intermittent fasting is using the same reasoning – instead of using the fats we are eating to gain energy, we are using our stored fat. That being said, you might think it’s great – you can just fast and lose more weight. You have to take into account that later on, you will need to eat extra fat in order to hit your daily macros (the most important thing). If you’re overeating on the fats here, you will store the excess anyway.

Like I said, it’s more for the convenience for timing, rather than the overall weight loss effects that it may have. There are other benefits, though, and we’ll discuss these too.

Benefits of Intermittent Fasting

There are a number of benefits shown that come from intermittent fasting. Some of these include blood lipid levels, longevity, cancer, and testosterone levels. The main two I want to focus on are the basis of our every day lives.



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People are always saying that if you don’t utilize the importance of pre and post workout meals, you are going to be losing muscle when you work out. This isn’t necessarily true, and it is even less so when you are adapted to ketosis.

Fasting while training can lead to a number of benefits in the long run, including:

  • Higher metabolic adaptationsStudies show that your training performance will increase in the long run when you are exercising in a fasted state.
  • Improved muscle synthesis – Studies show that muscle gains are heightened when you train in a fasted state, and utilize proper nutrient intake.
  • Improved response to post-workout meals – Studies show that the speedy absorption of nutrients after a fasted workout can lead to better results.

There’s been numerous studies on fasting while training, including one on Muslim athletes during Ramadan. It concluded that there is no effect on performance in training while fasting – so you have no need to worry.

Mental Clarity

Once your body is keto-adapted, your brain can effectively run on ketones, which are derived from fat breakdown in the liver. Fat is considered one of the most energy-efficient fuels for your body to run on, and your brain is a huge consumer of energy.

Most of the high carb advocates are running a campaign on the deprivation your body gets when you do not continuously refuel on grains and fruits.

Gain focus through fasting
They want you to be carrying around an apple and a granola bar wherever you go, but the beauty with keto is that you don’t.

Even if your body is out of glycogen (which it most likely is if you’re in ketosis), it can rely on the abundance of fat from the foods you eat and stores you have. That means your powerhouse of a brain can run full power all the time. Less mental fogginess, and more focus.

As you get used to fasting, you should start to fast naturally. Meaning, only eat when you’re hungry. Don’t plan your fasting – let it happen naturally.

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  1. Do you do intermittent fasting? Let me know your experiences :)

  2. Are BPCs allowed during fasting or is water only allowed?

    • BPC is allowed as a replacement breakfast, as it’s a liquid and just to get a slight start to the metabolism. I wouldn’t suggest drinking more than 1 though, if you need more coffee just make it a regular – black.

  3. Craig, is it necessary to wit until fully keto adapted to do intermittent fasting (16/8) or can we start just being in ketosis?

    • Keshia,

      You can start whenever, but know that if you do IF it shouldn’t be for weight loss purposes but for convenience or health benefit sake.

  4. Hey there if I run first thing in the morning – run for 60 min then some weight lifting. Do you recommend Tasty Bpf prior???

    What is a sample of your day while fasting?

    • Yeah you could drink BPC prior. Normally you can run fasting, you might want to drink the BPC prior to lifting. My 30 Day Meal plan breaks down how I eat right now (or a similar example of how I eat). You can check it out if you’d like.

  5. Hey Craig I am a small person (105lbs 5’3″) and I’m in the Keto world for the health benefits and mental clarity. I don’t really get hungry anymore but I just recently got over the headaches, nausea and fatigue. I had the BPC and then waited the 12 hours and had a spinach salad with roast beef, ham, vinaigrette, hummus wrapped in cheese (if you haven’t tried this it’s delicious, just load hummus onto a slice of cheese, roll it up, and noms).

    The problem was that I got really weak during the hours of not eating (without being hungry or anything, just weak) even though I was drinking water almost non stop. I don’t want to give up because I also felt a huge burst of energy when I ate again and more mental clarity than ever before on this diet.

    What can I do to stop the weakness without having to eat?

    • Ainsley, how long have you been doing IF? You need time to adapt to it. If you are not fully fat adapted then it might not be advised to do IF since you will get weak. I can’t think of anything that would cause this besides not being fat adapted or because you’re body is still adjusting.

  6. Hi, Can you tell me when i fast should i still eat my full days calories in the time slot for eating? It seems a lot to cram in over 3 or 5 hours. Or have i missed something somewhere. Thanks this really is an awesome site.

    • Hey Rebecca, yeah you have to eat all your days food in those few hour window. Usually it’s not as hard as it seems honestly. I’ll do it in 1 small meal to break my fast and 2 bigger meals in my window.

  7. Hi Craig,

    Been trying to find a straight answer does IF help with fat loss? You mention in this article that “there are no studies on intermittent fasting that show clear weight loss benefits” so does that mean you feel there are no benefits? In your 30 day guide and IF on Keto diet articles you mention it can be used to help with plateau’s and help you burn your own fat stores instead of the fat you get from food this would tell me there are benefits? If you are IF and burning your own body fat that would have to be benefits as long as you don’t regain the fat by over feeding. Let me know what you think. Thanks.

    • Les, there are no actual studies that show it helps with fat loss. You shouldn’t use it for fat loss, either. Keto alone will burn bodyfat, and in combination with IF it might have a slight advantage but I certainly wouldn’t use it if your intent is fat loss. Like I said in the article, only use it for convenience sake over anything.

  8. Hi Craig,

    First of all, what a wonderful site man. Great job!

    I am new to Keto but have been doing IF for about 5-6 months. Recently started following the 16/8 leangains protocol having previously followed the 20/4 protocol which led to weight gain… I have not lost weight even after cutting my calories down significantly and that’s why I am trying to incorporate a ketogenic way of life to get ripped. My stats are – (F/35/143lbs).
    I just have a couple of questions.
    1. Would it be wise to still do my morning fasted training and break my fast with BPC around midday then just eat one meal around 6pm? I take amino acids after my workout leading to my lunch.
    2. How much calorie deficit can I cut down to to lose more body fat? Currently eating 1800-2000 calories (pure keto – 65% fats, 35% protein & 5% dietary carbs)

    Appreciate your wisdom man! Thanks.

    • Hey Tahlita,

      Everything sounds good to me but I suggest going lower on the protein. You should only need around 1g protein per pound of lean mass to get proper muscle growth during workouts (I link the studies in some of the workout articles). The BPC sounds fine to me though, you just want to cut back on the protein a bit. Too much protein will just convert over to glucose and put you out of ketosis – keep your eye on that so you can become properly fat adapted.

      As for your caloric deficit, it kind of depends how much you’re working out. 2000 sounds good but I can’t always tell you if that IS actually good, because I don’t know what you’re doing in the gym and whatnot.

      Hope that helps and thanks!

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