Six Facts on Fasting

By The Fat Professor, Grant Schofield

It was unimaginable to me that I could possibly go a day without eating, let alone several. Yet, after adopting a Low Carb Healthy Fat lifestyle, I noticed that the pangs of hunger which would drive me to the fridge had somehow magically melted away, and I was no longer a slave to eating every few hours.

So what had happened – and is it a good idea to miss meals, or even a few days of meals (or more)?

Here are six things I’ve learnt about fasting over the last few years. Don’t miss point 6, it’s my “interesting fact” for the day.

  1. Fasting is easy if you are fat adapted, hard if you are not. Fat adapted means eating low carb for a few weeks and letting the body develop a better pathway for oxidising fat as a primary fuel source, especially using ketones for brain fuel. When you have a brain that is able to operate on ketones and can do so easily, then missing a meal (or several) is super easy. In my experience it’s even easier if you are busy, especially the compressed eating window (where you narrow the time you eat in a day to just a few hours).
  2. It’s a bigger step to move from a day to several days fasting.  You do have your ups and downs, most of these are behavioural, especially if you have children. In my world, eating with my family is big deal and we have three boys; two teenagers. While we could leave them to their own devices for the time we’re fasting, that is probably negligent parenting. In reality they’d end up buying Burger King or similar for their evening meals, which is parental negligence. For me, preparing food for kids, while never eating anything myself is nowhere near fun. It’s not that I am hungry really, it’s just something biological about the preparation and smell of food that activates things that I am trying to avoid.
  3. Mental clarity is enhanced. At least that’s my experience. I find the days when I skip breakfast and eat later in the day are my most productive. So much for breakfast being the most important meal of the day. Three days into a fast and I’m generally firing on all cylinders and get my best work done.
  4. Sometimes my sleep is not as deep or as long, but I still feel OK. For me, this is generally the reason I end up breaking a therapeutic fast. By day 4 or so, I find that I am losing sleep quality and quantity. I like sleeping, so that’s a negative. I reckon the sympathetic nervous system is primed in a “I’m ready to go and find (hunt) food no matter what” evolutionary sense. I don’t think there is much research on this, but it’s certainly something I experience.
  5. You might age slower – the latest research into how and why we age identifies a pathway called mTOR (mammalian target of rapamycin) as a key controller of the energy production process in the cell. In their 2013 Nature paper, Johnson et al. show that reducing mTOR pathway activation slows ageing. A second pathway which has the opposite effect is through AMPK (AMP-activated protein kinase). AMPK keeps cells healthy through a self-maintenance program, and helps them die when they should die (programmed cell death). mTOR is anabolic (growth) and AMPK is catabolic (breakdown and repair).

We need both anabolic and catabolic states for health. But the problem is the growth (anabolic) phase ages us, and the modern high-carb diet never allows us to get back to the catabolic state. Fasting and LCHF allows you to reach that catabolic state again. Your body has the right signals to preserve and repair cells, and kill off the ones that are past their use-by-date. The high-carb diet drives constant growth signals that result in cell damage without taking stock and repairing the damage. This is ageing.

Johnson, SC, Rabinovitch, PS & Kaeberlein, M (2013). mTOR is a key modulator of ageing and age-related disease. Nature, 493, 338–345.

Fact 6: If you have enough body fat you can fast for a very long time.  The world record for a supervised therapeutic fast is 382 days. It was set by a Scotsman in the 1960s. Here’s some interesting extracts from “Features of a successful therapeutic fast of 382 days’ duration”, published as a case report in the obscure Postgraduate Medical Journal (1973) 49, 203-209

“Patient A.B. aged 27 years, weighed on admission 456 lb (207kg). During the 382 days of his fast, vitamin supplements were given daily as’Multivite’, vitamin C and yeast for the first 10 months”

Results: Body weight loss

“During the 382 days of the fast, the patient’s weight decreased from 456 to 180 lb. Five years after undertaking the fast, Mr A.B.’s weight remains around 196 lb. “

In discussing the extremely low blood glucose levels…”Despite the hypoglycaemia the patient remained symptom-free, felt well and walked about normally.”

Last…“No faecal collections were made, but evacuation was in fact infrequent, therebeing 37-48 days between stools latterly.”

So there’s your interesting fact for the day! Fasting, despite the fact that a few years back I would have openly ridiculed people who fasted as fringe nutcases, if you haven’t fasted then it’s worth a crack and probably quite good for your brain and body.  You’ll at least learn a thing or two about your own physiology while you are self-experimenting.

Join the discussion 22 Comments

  • Jodie Atkin says:

    I have done LCHF on and off for a few years, mostly off as I keep falling back to old habits and easy options. I am now getting myself prepared to try again as I have a lot of weight to lose – 30kgs, but I’d be happy to lose 20kgs. My plan is to get back on to LCHF and then introduce IF. My question is, will LCHF and IF benefit me given that I have Hasimoto’s disease? I am wondering if Hashi’s raises any particular issues or whether LCHF and IF might have different effects in a person with Hashi’s? Thank you

  • Sandra Hawkins says:

    Tania…if you want to know facts about intermittent fasting ….there is a group on facebook that has reliable information. The info in this article is nothing like my experience with intermittent fasting. I am on day 132. I have lost about 34 pounds since April 17.
    I started IF because I had hyperinsulinemia, Hashimoto’s disease, hypothyroidism, and an immune deficiency. After 72 days it became apparent that the intermittent fasting was causing y Hashimoto’s to go into remission. All my labs looked better. My doctor was so impressed with my results that he and his PAs are committed to doing the research and using IF with their patients.
    Dr. Jason Fung uses IF to correct type 2 diabetes. You can access his videos on youtube….and he has a blog called Intensive Dietary Management. You can read a lot of good information on there.
    It is NOT necessary to go on a low carb diet to do IF. I eat what I want. You can deplete your glucose stores in 2 days and convert your body to a fat burner.
    Join the group, read the info. There is a book that gives you all the scientific information with links to the research. I am in no way affiliated with this other than being a member of the group. I was getting sicker by the day and a friend told me about intermittent fasting. It has saved y life. I am 60 and this was my last chance to get my life back. IF changed everything for me.

  • Tania says:

    I’ve only done overnight fasting 13-14 hours but am looking to extend.

    Can you please help with what to eat during a fast? What about 5-6 grams of collagen powder. Would that spike insulin?

    How do electrolytes affect insulin levels? If you take salt, lemon water or electrolytes is that still fasting?

    • What The Fat? says:

      Hi Tania,

      taking electrolytes during a fast should not affect insulin levels, and some longer modified fasts also use a green vegetable broth, keeping calories low. Because the balance of electrolytes will be important, the broth is probably a good way of ensuring this.
      The use of gelatin (similar to collagen) for modified fasts has been dangerous in the past, the reasons for this aren’t well-understood, but if there is to be a low-calorie food source a real food like a broth is better than a purified protein.

  • Amy says:

    Hi, I have been given a powder that you make into a drink to enable/aid in ketosis & was wondering if you’d heard of it (Keri OS) & what your thoughts were on it? I need to lose 10-15kgs & am struggling so need to change my eating habits & up my workouts. Thanks!

    • George says:

      Hi Amy,

      Keto OS is a form of endogenous ketones; what these do in a weight loss scenario is still unknown. They’re not being produced by your body burning fat, but they may suppress appetite; however some people report this is followed by hunger – so it’s a question of experimenting to see if they can be made to work for you.

  • Stephanie says:

    Your message is awesome, thanks. Is there any information coming out for kids, especially first foods. I believe we have always given babies to many carbs especially at breakfast, any thoughts?

    • What The Fat? says:

      Hi Stephanie,

      we’ll have a What The Fat for families book coming up, probably next year; until then I think Tim Noakes’ book Raising Superheroes is a great discussion of this question.

      • Stephanie says:

        I can’t wait, I hope it includes a chapter on first foods for babies for new parents.
        I will look out for Raising Superheros. Thanks for all the great work you and your team do in the area of LCHF, especially wanting to improve health outcomes for New Zealanders.

  • Lizette says:

    Hi there thank you for a great post

    Must say for the first time I hear someone that have the same experience than me, if I fast for 2 or 3 days I cannot sleep at all, my system is switched on and I am wide awake, wonder if this will change because I would like to fast for longer periods of time..

  • Since I have chosen to cook for my wife over the last 3 years because I wanted us to go LCHF, I’ve found it quite easy to still cook a variety of foods for her while I’ve fasted for up to five days at a time. This may be partly because, for the last 14 months, I’ve been eating no plants and have necessarily had to prepare us separate meals anyway. Anyway, people may find it easier than you suggest to cook for someone else when they are fasting – that is my n=1 experience anyway.

  • Pedro says:


    Great article, well done!

    Over the past 2 months I have been naturally doing 20+ hour fasts and I workout in the fasted state (HIIT or resistance training). After my workouts I’m even less hungrier than before the workout, which from I know is caused by a post workout enhanced ketosis effect. When I break my fast, I get full very easily and quickly, but I also want to reach a certain amount of protein and fat that allows for muscle protein synthesis. Should I listen to my body or should I make sure I achieve those macros, particularly on training days? I obviously want to burn fat and build muscle, but altough the training stimulus is the key for hypertrophy, I’m afraid that if I don’t achieve certain macros, I won’t see the muscular development I am training for. Can you please share your thoughts on this?



    • What The Fat? says:

      Hi Pedro,

      Grant says

      “There may in fact be an even greater anabolic effect by leaving refueling longer because it’s just more metabolically stressful. But the trouble is you will take longer to recover before the next exercise bout.

      I pretty much do what you do and don’t worry about eating until I feel like it, but I am not training that much, or that seriously. I reckon if you are really serious you should eat as soon as possible to get the protein in and generate an anabolic response.”

      If you are specifically interested in bulking up, protein timing only matters at a high degree of training; for the average person it may not be that important (see here ).
      As for macros, I would trust your appetite when it comes to how much protein; only if you aren’t getting results, then try to increase the protein-to-energy ratio.

  • Andrea says:

    Hi. Is it more beneficial to do one long fast, or could you conceivably fast for one meal a day (for example) over an extended period of time, to have the same results? And what type of weight loss would you typically see, from say a three day fast? Thanks

    • What The Fat? says:

      Hi Andrea,

      we usually start with intermittent fasting, or time-window restricted fasting; this could mean skipping breakfast, so that there are about 16 hours between meals. This is easy, and is long enough for health benefits of fasting. This can let you know what it would be like to fast for longer, whether this is necessary or tolerable for you – it’s good practice, and for many people is all they need. The calories you would burn in a day without eating, if they all came from fat, would be about 150-200 grams of fat. I hope this answers your question,

  • Josh says:

    With fasting, I’ve always wondered if having multivitamins/Pro-biotics/nutrient drinks. I take a probiotic powder which includes some food nutrients in it as well, but I was wondering if taking it effectively stops my fasting period??

    • What The Fat? says:

      Hi Josh,

      the calorie and carbohydrate content of supplements would affect a fast; as little of 7 grams of glucose can interrupt ketosis. There’s unlikely to be much digestible sugar in a probiotic powder – most of it will be fibre, but I do wonder if it’s necessary to have probiotics when you’re not eating? On the other hand broth and other things people use during fasts do supply a few calories, so I suppose the answer is likely to be, that it won’t stop the fast, if it helps you through it.

  • Jo Holt says:

    Great post. I have been LCHF for about several years (so am fat-adapted) and recently started experimenting with intermittent fasting. As a woman, I am also interested in your view on gender differences in fasting? I find I do well on a 16:8 fast but not on anything for a day or more and have heard that there can potentially be more issues for women than men? Thanks for these articles – fascinating, keep them coming!

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