Grabbing the Bull(shit) by the Horns!


Over the course of the past week I have literally spent every moment of spare time that I have trying to pick through fact from fiction when it comes to fasting, health improvement and weight loss. I was literally reading so much conflicting advice from so many different sources I felt confused, unsure, disillusioned and increasingly desperate.

I mean, how bloody hard can it be? Go without food, be healthier, yeah? Well, no, as it turns out.

You’ll find some sources telling you to do a daily fasting schedule, some telling you to do it alternate days, some only for a couple of days, some telling you to fast for many days at a time every couple of months.

That conflicting advice was just to do with ‘when’ to fast! When you start reading about ‘how’ to fast, the advice starts to become even more contradictory. Some say no food, water only. Some say one meal only, some say many smaller meals. Some say you should drink replacement shakes, some that you should drink only very expensive prescribed (by the companies that make them) detoxifying juices.

Surely a feed days easy isn’t it? EAT?! Apparently not, take your pick from low carb, low protein, calorie restricted, calorie overload or just sit in Mcdonalds all day, feasting until you explode, because (apparently) it doesn’t matter, just as long as you go hungry tomorrow……

My brain was mush by the end of all that ‘research’. So much for making everything clearer! It was a vicious cycle of new ‘fact’ contradicting yesterdays advice, then while researching the validity of the new ‘fact’, a new ‘fact’ would emerge!


Either I was going to have to just give up on this whole fasting thing and just calorie restrict (probably unsuccessfully) again or I was going to have to get to the bottom of this once and for all….

So, I grabbed the Bull(shit) by the Horns and decided to use the Internet for information (rather than advice) and found contact details for the four scientists involved in the Horizon documentary .

This was surprisingly easy, and within an hour I had written a long email explaining the confusion with the contradictory protocols and explained to them that I was interested in a 5:2 intermittent fasting protocol, primarily for the health benefits with the weight loss a nice bonus. I pointed out that I was finding it difficult trying to get to the very basics about what has actually been shown to work.

The scientists that I approached (in order of appearance in the Horizon documentary) were:

Luigi Fontana – the segment with the Cronies and Dr Mosely physiological profile and tests.

Volter Longo – the segment with the 4 day fast and discussion of longevity and IGF-1 (Insulin like growth Factor 1)

Krista Varady – the segment on Alternate Day Fasting

Mark Mattson – the segment on Alzheimer’s and the response of the brain to fasting. He was also the scientist that suggested the 5:2 protocol to (the presenter) Dr Michael Mosely.

Within a day, 3 out of 4 of the scientist had responded to my email. I was so pleased!! To date, Luigi Fontana still has not responded. But, hey, a 75% success rate was pretty good, right?

The great thing about their responses was that they were relatively short and straight to the point. Exactly what was needed for the sake of clarity! Mark Mattson also sent me several studies that he thought would be of interest to me, which I thought was very helpful.

Let me now sum up what each of them had to say to me, and also what they have said in some other interviews that I have seen.

Luigi Fontana

Advocates fasting (within the context of 24 hours) for as long as possible. He suggests that if you have to consume 5/600 calories then they should be consumed as one meal, very early in the morning so as to maximise the length of the fast.

Volter Longo

With regard to IGF-1 reduction:

The evidence indicates that it is better to do 4 days of (consecutive) fasting every few months and then skip meals during the week to maintain weight and try to adopt a plant based low protein diet.

An alternative (to the 4 days fasting) is just to fast on 2 days at a time as in the 5-2 plan but you must also try to move to a healthy diet, plant based and low protein.

He didn’t make it clear if those 2 fast days should be consecutive on the 5-2 plan or how long the fast should last. Since we are dealing in ‘facts’ here, I don’t want to guess what he meant, otherwise this information is no better to you than all of the rest of the confusing information that I have read. You don’t want to know my opinion, you want to know his. So let’s stick to the facts:
Either fast 4 days (consecutively) then skip meals and eat a plant based low protein diet, OR fast 2 days per week and eat a plant based, low protein diet.

Krista Varady

With regard to how you should eat (if at all), on a fast day:

So far, we have performed studies permitting people to eat 600 kcal between 12pm-2pm. We find that this strategy works well for most people (whereas a complete fast for 24 h does not). We have yet to run a study where we allow people to consume the 600 kcal as 6x100kcal (or 3 x 200 kcal) smaller meals throughout the day. However, we are planning to run this study within the next year.

Again, let’s deal with facts: there have been no studies done yet that show whether eating during a fast is effective or not. They are going to be doing a trial later this year to ascertain this. Dr Varady invited me to contact her later in the year and she will give me an update on how the trial is going, which of course I will share with you! What I can tell you for a fact is that Krista Varady is already of the opinion that ‘eating the 500 calorie allowance throughout the day would prevent a persons body going into a fasted state’

Since it is the fasted state that is so beneficial to us, this information is critical. This tells us that abstinence is the best policy while fasting, but it doesn’t tell us for how long.

Mark Mattson

These responses are based on our recent animal and human studies:

1. A complete fast (no food) with hydration maintained with non-caloric beverages will be superior to consuming 600 calories on the fasting days.
2. Eating the 600 calories at one meal will be superior to eating several smaller meals spread throughout the day. By eating only one meal, the body goes essentially 24 hours with no food. This results in adaptive cellular stress responses which we believe is particularly good for the brain.
3. In the case of the 5:2 diet, we do not know whether better health benefits are realized with two consecutive days of fasting versus any two days of fasting during the week.

So let’s cut to the chase: it would be much better if you could just get through a fast day without eating at all. Obviously, very few people are able to, or want to go for 36 hours without food. So if you are going to eat a (600 for a man, 500 for a woman) calorie reduced meal, you are much better to consume that as one meal than to spread those calories throughout the day.
This is because the stress produced by going for 24 hours without actually has identifiable positive brain responses such as the growth of new brain cells. It’s like a workout for the brain. How to add that into an intermittent fasting or alternate day plan?

Easy. Either, take a note of what time you last ate on the feed day prior to your fast and then do not consume your 600 calorie fast day allowance until 24 hours has past. So, if you ate at 6pm on a feed day, do not eat your 600 calories until 6pm on the fast day. That way, you’ve gone 24 hours without food AND you get to eat (albeit a restricted) dinner! If that doesn’t grab you, eat breakfast on a fast day and then don’t eat again until your breakfast the next day.

Hopefully this information has helped to give you a little clarity….


Blogging my journey at

Twitter: @thePRIMALme

You can also find fellow fasters @FeedFastFeast and also in the Facebook Group



36 responses to “Grabbing the Bull(shit) by the Horns!

  1. I am really impressed that you wrote to these people and REALLY impressed that they replied! I am looking forward to seeing your revised diet plan and I am wondering whether the importance of restricting protein figures in it. This is the hardest thing for me, especially as plant protein is better and I am not a vegetarian!

    • Thanks Wendy. I’m not a vegetarian either, so hopefully we can find solutions together that involve still eating meat! Vegetarians don’t have it so easy you know. I realised very quickly that when trying to limit protein, there seems to be plenty of sources around that are veggie friendly. Even my wholemeal pasta has protein in it!!

      As far as I’m aware, what is meant by a ‘plant based, low protein’ diet, is that the diet is based on a ratio of under 0.95g protein per Kg of body weight (or stick within current RDA recommended daily amounts).

      The ‘plant based’ aspect means eating a more ‘natural’ diet. For example, instead of adding carbohydrate to your diet in the form of white pasta, you could substitute it for a more complex carbohydrate, such as butter beans. Or for you burger fiends out there, you could try eating your beef with some vegetables instead of picking it up in a chunk of bread! Hehe

      I think when it comes to diet you’ll get so much good advice on what to eat and what not to eat by researching a low GL (Glycaemic Load) Diet. I eat by GL principles all week except for the weekend when I have a Feast. I mean, after all, who could ever imagine NEVER eating a cake again!

      I’ll try and get my revised plan uploaded this evening or tomorrow morning. I’ll include details of a sample eating schedule that i’m following if that helps. I’m no expert, but it might be of interest to you :o)

  2. Pingback: FeedFastFeast: The 5:2 Diet and Exercise Plan « FeedFastFeast: The 5:2 Diet·

  3. Fabulous stuff – I empathise entirely with the feeling of information overload. This post sets it all out beautifully – cheers!

  4. Hi. Yes, I’m also very impressed by your research into the subject of 5:2 diets. One question, though: if 24 hours provides the optimum time span in order to gain the maximum benefits a complete fast day offers; assuming too that you choose to spread these two 24 hour fasting days throughout the week (i.e. not consecutively) what’s to stop one from dispensing with the single 500/600 calorie meal altogether? What I mean to say is that you could stretch a complete ‘fast day’ over a 24 hour period – say, from 6:00pm one day to the same time the following evening – and still end the fast with a normal ‘feast day’-style meal. In other words, you would still reap the benefits of having eaten absolutely nothing over a 24-hour period, without having to restrict your food intake to a 600 calorie meal at the close of it. Again, this regime would only work (assuming it works at all) on non-consecutive fast days. If so, is this an instance of having one’s cake and eating it?

    • Hi,

      I’ve been answering this question a lot recently in the Facebook group.

      The way I look at it is to separate the fast from the calorie restriction. See them as two seperate things.

      The 24 hour fast produces the health benefits and the 5/600 calorie meal provides severe calorie restriction on fast days, allowing you to eat a little more on feed days than a normal daily calorie restricted diet would allow.

      What I would say is that when I reach my weight loss / fitness goals I will still continue with the fasts but allow myself a much more generous calorie entitlement on a fast day.

      Hope that helps :o)

  5. thank you so much for this it has been driving me mad trying to work out the ‘right’ way of fasting – I started this a while ago because of the simplicity of it and the amazing health benefits but I found that the more i looked into it the more confusing it became. I am struggling to lose any weight but I think that is because I have jumped from 5:2 to ADF to eat stop eat and never actually settled with one particular way! I will now vow to stop researching (after all you have done it all for me) and stick to FeedFast Feast!! Thanks again :o)

    • Definitely look into Low GL (not Gi) as well because its a great compliment to the fasting.
      The fasting helps to lower insulin levels, allowing your body to go into fat burning mode rather than storage mode. A low GL diet actually is very effective in keeping insulin levels low as well because the foods that you eat are not creating great spikes in blood sugar that in turn causes steep hikes in insulin levels.
      I’d highly recommend any of the GL books by Nigel Denby or Patrick Holford if you’re interested in looking into it further.
      Best of luck :o)

  6. Thsanks-it is as readable as anything I’ve seen.
    What I struggle to get is a concept of what constitutes a 600 cal meal-are there any places where there are indicative meal plans for a 600 cal meal?

    • Have you joined the Facebook group David? We’re going to start posting some recipes in there. I’m also going to post them on the blog too, so if you don’t use Facebook, don’t worry you’ll get them here.
      A lot of people get phased by a 600Kcal meal, it doesn’t have to be a tiny dinner if you choose ingredients properly.
      Also I just had a little look and the BBC Good Food website has a recipe search. If you look below the search box you can refine the search and one of the criteria is ‘select calorie range’. That might be helpful:
      Best of luck, if you need any more help give me a shout :o)

  7. I started about 4 weeks ago and so far have lost about 10 lbs. I eat my 600 cals in 3 small meals on the fast day, which I find fairly easy to keep to. I dont know if I am getting any of the health benefits yet but I do feel a lot better, more energy etc. So I am doing it as suggested by Michael Mosley in the Horizon programme and we know he gained the health benefits as well as losing weight. So I am reluctant to change to complete fasting or just one meal as I think it would be much harder. If it worked for Michael then that’s good enough for me.

    • Well done Richard, that’s great progress!

      I wouldn’t put yourself down though about what you can and cannot handle, I’ve spoken to quite a few people that thought they’d find it too difficult to eat their calorie allowance in one meal but were surprised when they tried it that not only could they manage it but that it was preferable for 2 psychological reasons. Firstly, they like having a ‘normal’ meal (usually in the evening) perhaps of more than one course and secondly they achieve a sensation of defeating hunger, that they realise they actually can go without. I even had a conversation with a couple of people who said that it had been an enlightening experience because it had made them contemplate how others in the world that have no food must feel on a daily basis and it made them feel silly for worrying about it when they knew they could go back to eating normally the next day.

      However, saying that, I’ve also spoken to some people that have tried it and found that they just couldn’t do it. In those cases Its obviously better to still be doing something than doing nothing. Having a couple of severe calorie restriction days seems to be a version of calorie restriction that people find palatable rather than a standard daily reduction. There are a lot of health benefits from ‘dieting’, we saw that with the CRONIES on the documentary.

      Best of luck in 2013 for the healthier new you. :o)

    • Ps I tried the complete fast once (and only once!!) ie zero calories on a feed day and I didn’t like it, so would never have been able to stick to it.
      Again, I’ve spoken to a few people that do that on alternate day fasting, so in essence have a 12hr eating window every 48hrs. I’d struggle with that!
      I’m switching to alternate day fasting, (Professor Krista Varady spoke about it on the Horizon documentary) but as my fast starts at lunch and lasts until the following lunch, I’ll definitely be eating (prior to starting) on a fast day.
      I’ll be posting later on today about the plan we’ll be following.

  8. Many thanks for the very informative & accessible research – hubbie & I saw the documentary & are starting the 5:2 fasting this week…like you I wanted to know what the research said about the difference between fasting and calorie restriction, and what exactly constitutes fasting. We had heard that you could eat in 2 meals but your answers so far seem to suggest that to get real benefit only 1 meal in the 24 fast so I think we’ll try that. Did Dr Varady get back to you yet about the additionalresearch into this?

    • Actually it’s funny that you should ask that because I asked her about that last week and she said that they’ve secured funding and will be starting the research in Spring and hope to have preliminary results in early Autumn.

      We’ve moved onto alternate day fasting. I like the simplicity of day on day off. Early days, We’ll see how we get on.

      Best of luck with your fasting plan :o)

  9. Hi, did you ever contact Dr Michael Mosely about his thoughts and subsequent trial results from his own intermittent fasting experience?

    • No I didn’t. Dr Mosley shared that information quite openly on twitter and has written a book about it.

      I was more interested in contacting the ‘experts’ to try and get to the bottom of some of the confusion surrounding what constitutes fasting. Dr Mosley was a user of intermittent fasting, just like us, the experts are the ones that are pioneering this fascinating subject so I thought their input would be more valuable.

  10. Hi Mark,
    I notice that Dr Mosely says in his book ‘the fast diet’ that his IGF-1 reading went down from 28.6 nmol/l to 15.9nmol/l after 3 months of a 5:2 regime with calories split between breakfast and supper. He says: “For me, the particularly pleasing changes were in my fasting glucose levels and the huge drop in my IGF-1 levels, which matched the changes I had seen after doing a four-day fast”. Obviously it is not a scientific study but I find it interesting that, in his case at least, fast-like benefits seem to have resulted from calorie restriction rather than a 24 hour zero-calorie fast.

    • IGF-1 levels can be lowered through diet alone so are not a great indicator of the effectiveness of fasting. In the BBC documentary Dr M stated that he was lowering his protein intake. In a study conducted by Dr Luigi Fontana he managed to lower IGF-1 level in a group of Cronies (daily calorie restrictors) by limiting their protein intake (this is off the top of my head so excuse any errors!) to around 0.95g protein per Kg of lean body mass.

      A proper study would have to be conducted to determine whether calorie splitting is as effective as zero calorie fasting. Dr M’s results are anecdotal and a study of one. For what it’s worth, regardless of what has subsequently been written in the book, Dr M is definitely doing 24hr fasts in the original documentary. Check out the footage again and you will see that on his walking holiday he quite clearly states that he’s had breakfast and will not eat again until the following morning. A lot of confusion has arisen since the documentary, that’s why I wrote to the scientists to get to the bottom of which way would be best for health benefits as opposed solely to weight loss. I’m not saying that the ‘fast diet’ approach doesn’t work. I can’t know that. All I know is that it hasn’t yet been tested.

      Finally, on the subject of testing, Dr Krista Varady is conducting research this year into ADF and calorie splitting. Preliminary results expected in Autumn 2013.

      • Thanks Mark, I look forward to Dr Varady’s results. In the meantime I have to decide whether to change the regime I’ve been following since August and have got comfortable with, which is 5:2 with calories split lunch and supper. I’ve lost a load of weight and am feeling fitter than for a long time, but my real objective was the health benefits mentioned in the Horizon program. So my basic choice now is whether I’m going to skip lunch – think I’ll probably try it and see if I think I can maintain it long term.

  11. I’m confused as to whether low protein intake is required for any of the fasting protocols to be effective. Dr M seemed to ignore this at least for the 5/2 protocol when he ate large hamburgers etc. on his feed days.

    • Fasting produces more benefits than IGF-1 reduction so fasting protocols are effective for health anyway. With regards to their impact on IGF-1 reduction I’d say that so far the research shows that fasting alone will not reduce and maintain IGF-1 levels if the person is consuming a diet high in protein.
      As for Dr M, unless you knew what else he ate on his burger days you can’t be sure that he was eating excess protein. For all we know that was his only protein source that day.
      You, nor I, know what Dr. M did or did not eat and in some ways it’s really quite irrelevant because we can’t use anecdotes as a replacement for research. What works for one does not always work for another.

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