The importance of protein on fast days?

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The importance of protein on fast days?

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  • I’m a little confused over the necessity or importance of including protein in your meals on a fast day. I must admit this passed me by (I’ve watched the horizon show and read the fast diet book several times) but in a YouTube clip I saw Michael mention in passing that you should eat protein on a fast day “because the body doesn’t store protein”.

    So I wanted to understand this better. What happens if my fast day meals include no protein, would I be losing muscle instead of fat or is there some other negative effect? If I make up my 600 calories from carbs and oil (eg pasta pesto) and add no meat how is this worse for me that the high protein low carb recipes Mimi shows in the book?

    The recommendation is clear enough (to eat 50g protein on a fast day) it’s the reasons behind it which I’m seeking to understand better. Thanks 🙂

    Hi MItch, Protein allows you system to pull out of the insulin spikes that are created by eating carbs. The less carbs you eat the less glucose spikes will happen allowing your system the time to rest and repair on fasting days. Carbs will also create more hunger as the day moves forward. In the intro to the cook book you will see that Michael talks about carbs on fasting days…and a fasting window between breakfast and dinner…it’s helpful to review 🙂 Hope this helps….

    If I recall correctly if you don’t eat enough protein on your fasting days your body will burn muscle instead of fat to get the energy and other nutrients it needs. Obviously that is not a good idea.

    Thanks both. This is certainly a detail which I overlooked in reading the book and viewing the Horizon show orignally. Sounds like I should ditch the pasta/pesto on fast days and get some omelettes going instead 🙂

    This is interesting, especially that the body will burn muscle instead of fat if there isn’t enough protein – but what about a liquid fast/juice fast?
    It’s very difficult, if not impossible, to get enough protein that way…

    In the book I think I remember that it seemed pretty flexible – as long as you fast or cut back to about 500-600 calories 2 or three non consecutive days a week it should work.

    I find it much easier to just drink coffee and water and maybe some tea and forgo eating all together – until evening. Seemed like the book allowed this. I suppose I could find a low calorie protein shake if there are such things.

    On the PBS video I thought that I heard Michael state (when he was driving with Valter Longo, Ph.D.) that eating protein was equivalent to having your foot on the gas in a go-go mode, and this would not give the body the necessary down time needed to repair the damaged cells. Yet, the recipes call for protein at each meal on the fasting days. So, I am confused. Thanks for any help with this.

    Hi susan j. As I understand it and Michael has said on page 77 of his book in the principles of what you eat on a fast day….”and the best options to achieve this are foods that are high in proteins and foods with a low glycaemic index (GI)”. H e goes on to say that protein helps keep you feeling fuller longer.
    So yes protein is required eating on your “Fast Day” not just to make you feel fuller but because of the other benefits it has for the body.
    Good luck.

    I have tested this on my fast days, some fast days I have had Fage (greek 0% yoghurt, 10 g protein per 100 g) and some days ryebread and ham. Both approx 130 kcal, but Fage seems to keep the hunger away for a longer time. Plus it is convenient to take a Fage to the office, and have my breakfast there.


    Considering what I normally eat on a fast day, I probably need to increase my protein intake quite a bit… interesting reading above. Would a blood test showing the level of protein in your blood indicate if you get enough protein or not? I saw that this was measured in my blood test when I had regular checkup earlier this year and it was all within normal ranges, so perhaps I should not worry… what do you think? Thanks!

    c what one of the authors said

    6:35 pm on 20 Mar 13
    Report this post

    TML – we suggest more plants and protein for a Fast Day and fewer carbs – particularly the fast-release ones you tend to find in commercial cereal/muesli bars. They tend to spike your blood sugar and won’t fill you up and keep you full. Better to go for bulk from veg, and some protein.

    Protein is important on a Fast Day, both for satiety and for retention of muscle mass. If you want carbs, a bowl of porridge would be a decent option.

    Thanks a lot for the quick reply! I just find it difficult to reduce the number of calories while still getting enough protein. One part of my diet on a fast day is typically a large portion of vegatables (low in calories, rich in vitamins and minerals – but also virtually zero protein). I guess that I will add some additional protein into that meal and then some more than what I already have in the other meal on a fast day. It is not that I eat much carbohydrates… I eat very little in fact, but I probably need to cut that out to give space for some additional protein.

    found this article 2 help concerning
    Lowest in Calorie
    7 Protein Sources that Are Lowest in Calories

    A high protein diet can help build muscles, and also help you eat fewer calories. Protein takes longer to digest, slowing the process down. When adding protein to your diet, eating lower calorie choices will help you control your overall calorie intake. Though there are a variety of plant and animal sources of protein, you will have no problem getting enough in your diet, without even a sprinkle of protein powder. No matter if you are a meat eater or a vegan, there are plenty of delicious options for you.
    Meat sources

    Meat sources are the highest in protein. Lean meats are the most often recommended sources of protein for people who are looking to build their protein intake.
    1. Ground turkey

    Ground turkey is a versatile choice that can be used to make burgers, meatloaf, meatballs, tacos or a tasty taco salad. Weighing in at 120 calories per 4 oz serving of extra-lean breast meat, ground turkey also packs 26 grams of protein. A decent iron source, ground turkey is a high-protein food choice.
    2. Chicken breast

    Almost as low-cal as turkey, chicken breast can be easy and low-maintenance, or elegant and worthy of a dinner party. Throw a breast on the grill, and you’ll get about 2 4oz servings out of it, and manage to keep your calorie count at a low 124 calories. At 24 grams of protein in that serving, you won’t go into calorie debt with this meal. Chicken breast can be served so many ways that you could do something new every day. Compared to your other meat sources, it’s also low in cholesterol.
    3. Filet Mignon

    This decadent steak is the highest in calories, with 244 calories per 4 oz serving, but with 32 g of protein, those few extra calories are worth it once in a while.
    Dairy Sources

    Dairy based sources of protein are a great option for people who don’t prefer meat. Milk, ice cream, eggs and cheese are high in protein, but low calorie options are available, too.
    4. Egg Whites

    Egg Whites are an easy-to-prepare choice, and are a great addition to salads, and they make a delicious omelet, breakfast sandwich or burrito. 3 egg whites make a substantial serving, but only contain a minimal 48 calories. They’re not as high in protein as meat sources, with 11g protein in those 2 whites, but they certainly leave you a lot of room in the calorie bank.
    Seafood sources

    5. Shrimp

    Shrimp is a really low calorie choice, but one that packs 18 grams of protein in a 4 oz serving, while only costing you 80 calories from your daily calorie budget. This quick cooking choice is great grilled, or boiled and chilled as a cocktail where you are adding on only minimal calories.
    6. Tuna

    Canned, grilled, seared or sashimi, tuna is tasty, low in calories and a huge source of protein. At 128 calories and 28 grams of protein per 4 oz serving, this is a worldwide favorite.
    Plant sources

    Plant sources like beans, bulgur and brown rice are great ways for vegans to get their protein, or for non-vegetarians to supplement their diets and change it up.
    7. Soybeans

    Edamame, or soybeans, are an excellent source of protein with 17 grams in just 1 cup of beans, but with only 189 calories. Soybeans are packed with iron, calcium and fiber, therefore make an amazing choice. Soybeans are a crowd-pleasing appetizer served boiled, and they’re tasty with rice or just sprinkled on salads after they are cooked.

    Perfect! I am very glad to see soybeans there as that is an important element in my element on a fasting day 🙂 – thanks for the help and have a great day!


    Very interesting on the protein ,

    I can recommend Skyr, the high protein and almost fat free islandic yoghurt. One container contains only 120 calories, which is a perfect meal.

    Tack Ninna 🙂 – not sure I can find it in Budapest… but youghurts are probably a good place to start:) – appreciate the help! I am currently mixing soy protein and a few tablespoons of extract from pumpkin, sesam or other seeds into youghurt or similar. It is packed with magnesium, iron, calcium and many other minerals (and actually tests better than it may sound :)) and also with protein. That is the main meal I have and then a big salad as the second meal on a fast day for the vitamins. The blood tests have not indicated any problem so far, but I probably do need to pay a bit more attention to the protein. I am a devoted runner and also try to keep my animal protein to a minimum, so now that my weight has stabilised where I want to be, I will take another blood test and just check that all looks fine. Probably, I will go on to 6:1 and see how it works over, say, 6 months.

    Just be careful with soya protein. It can cause thyroid problems.

    I have to repeat my reply on the protein deficiency page. I lift weights, have followed the 5:2 diet for 8 months at 36 hours at well under 600 calories and I eat no protein or carbs to speak of on fast days just a large salad. Net results is I am 10 lbs lighter than my already lean BMI and am lifting higher weights than ever. I am surprised as anyone but am convinced that Monday and Thursday 36 hours fasts with little protein does not cause loss of muscle.

    That’s good to read Wildside. I’ve been using an old italian recipe … making soup with onion, garlic celery, fennel, carrot and veg stock then breaking egg into it when hot.. (which works out at about 15g protein and 150Kcal for a generous portion, inc olive to saute the veg with first… (soup was found in prev programme to keep you full longer than a solid meal) the full recipe also has grated parmesan croutons in it but I skip them on a fast day… so I am well below the 50g of protein.

    NB 50g of protein is A LOT… bare in mind 1 chicken breast has about 23g protein and 100g grams of salmon about 20g… eating 50g of protein would probably mean going over the 500Kcal mark I think (approx figures from nutrition data).

    I think there is something about loosing excess fat making your body more efficient so needing less muscle to do the same work. I ride and have found I am much better balanced and can ride a lot faster now, my core stability has VASTLY improved…. lots of gallopy gallopy 🙂 makes both me and horse happy 😀

    Hi Ninna,

    interesting reading regarding the thyroid and I find it perplexing to hear soy protein as a mild cure against high LDL and in some reports a recipe for longevity (but possibly in the shape of tofu) and then also hear that you should keep down your consumption of animal protein and animal-like protein such as soy protein to maintain a low IGF1…

    I normally have around two tablespoons of soy protein a day. Do you have any idea whether that is a lot/too much? On a fasting day, I am still well below the 50g proteins with this as the supper is a plain salad.

    Thanks for your help and input so far, I am very happy for any input!

    I think I found it… they speak about a consumption of 30 gram of soy protein or more as a possibly unhealthy level of consumption.

    I also tested Skyr (Icelandic milk protein product), but I noticed that blueberry and strawberry are sweetened with sugar, other versions with acesulfame K. Artificial sweeteners are a no-go for me, due to previous bas experiences – and cancer risk. But I like blueberry Skyr (88 kcal per 100g), 170 g packed in a cup with a spoon is a mobile, protein-rich breakfast for me on fast days:D

    Thanks for the tip Ninna!

    How about the degree of completeness of protein? Some protein sources are not complete in terms of amino acid profiles, would complete protein be recommended?

    What’s been the research on zero food(water) alternate day fasting? Clearly zero food means zero protein, so if there’s any loss from low to no protein they should experience it.

    I’m new on this forum but i’ve been on forums all year and learnt quite a bit of new information about nutrition and weightless that i didn’t know before. and i’m aware that i don’t know everything even though sometimes it appear that i think i do. I actually came to this forum to ask about not losing muscle while fasting. But the answer to my question is not categorically answered above so i will start another thread for that.

    I wanted to say that i don’t think any of the posts have satisfactorily answered the OP’s question. I will make just a couple of points rather than go through my whole list of questions and objections to what’s been said. … Oh on looking at the last few posts i missed before, others are starting to raise the same things but i ‘ll repeat them anyway.

    This year i have been reading how bad soy is for us humans. It is ok to eat if it in a fermented state like tofu, miso and tempeh. All these soy products and shakes are said to be less than ideal for human health. It is better to get vegetable protein from the other beans and lentils than unfermented soy. And i even read that we westerners would tend to eat more tofu than say asians so its unknown if the amount we’d eat if relying on it for protein is healthful or not. On the other hand, maybe its ok in lower quantities. But anyway look into it. I think its telling that no other culture has made it a staple food product in its unfermented form. Part of the problem of soy is how they are processed. It cannot be considered a whole food when eaten in shakes and the like.

    Another point which i learnt from my recent experience with low carb is that the reason we need to eat 500 calories a day on a fast is so that our brains have access to ready fuel and i’m not even talking about protein yet. It takes some time doing low carb before our brains can get energy from fat so its first choice is glycogen from carbs and next up, – when we run out of glycogen stores – is protein from our muscles or diet. I”m hoping that 500 calories a day is enough to spare me losing muscle for this purpose but i don’t want to focus on protein on my fast day. If you are doing a one day fast then its unlikely you’d run out of glycogen in a day from your muscles but it could happen over two days i think. We also need the protein for normal tissue repair as well as now the possible need for brain fuel. It seems like the 5:2 book might not be very clear or detailed on the subject.

    50 grams of protein is a lot of food. Its not 50grams of steak for instance. So to get 50grams of protein, you do have to sacrifice quite a lot of other foods types to achieve it. I don’t really want to do that and would only do it if i have to. And someone else said, it seems to contradict the stuff about IGF1 unless, this is a low enough quantity not to upset the plan re the longevity matter – which i understand is not a done and dusted argument anyway.

    The tv show didn’t give us the bottom line information. It just showed us all the arguments (or maybe some) of the arguments out there at the moment. e.g. there is one case for saying that we may not be able to benefit from the longevity effects of low calorie diets unless its done from youth. There are still many unanswered questions on this topic so i wouldn’t get too concerned over it.

    But i refer the OP back to fourth paragraph for the direction to in for his answer. If we need protein its probably because of this and so ultimately eating it would is intended to prevent muscle tissue metabolisation. (if that’s a word).

    Whenever I hear of someone struggling with hunger or not feeling well on their fast-day the first thing I wonder is how much protein they are consuming on their first fast-day. (The second question is how much water are they drinking.)

    When I first began 5:2 I had godawful headaches on a couple of my fast-days. After I understood and addressed the protein issue… no more headaches. Not a single one.

    I believe the protein issue is certainly worth discussing with anyone who is struggling.

    I don’t eat any significant protein on fast days, only low cal vegetables. The idea that the body mines for protein from muscle is simplistic. Instead, the body up-regulates systems that scavenge for available amino acids. This would include mis-folded proteins like beta-amyloid and tau. The body probably also up-regulates destruction of damaged cells and cellular organelles. These things are what Dr. Longo was referring to as “repair mode” resulting from protein deficiency. The concept is that in hunter-gatherer days, protein shortage would be common and the body would leave off repairing all the damage that occurs over time in order to have a ready supply of amino acids. Then, when needed, amino acids are scavenged and repairs are made at the same time. Modern people rarely experience a dietary shortage of protein and therefore rarely enter repair mode and the damage just keeps increasing, resulting in cancer and alzheimers. Whether this is actually right and whether one day’s protein fasting is sufficient to make a significant difference, is a question, of course.

    Interesting input dl. Can you please refer us to some more material to go into this in some more detail. Also i am not great with the scientific vocal you’ve used so its hard to understand some of it. Do you know any sources that speak in layman’s terms.

    What do you mean by up-regulate?
    What do you mean by mis-folded proteins?

    It was a new one for me to read that headaches are due to lack of protein. I was led to believe from my low carb reading that they are due to dehydration stemming somewhat from electrolyte imbalance or just dehydration from reduced food intake. It can’t really be from lack of protein because on low carb diets, people eat lots of protein. The headaches are mainly in the beginning before they starting making ketone bodies.

    On the other hand, at the beginning of a low carb diet which i think is similar to a fast day -because carbs are usually pretty low on a fast day as well, is the brain getting enough fuel. I had thought that any fogginess or funk could come from a lack of fuel but i haven’t noticed any of that on a 500 calorie fast or in low carb. I did notice it on a water fast. When my brain is just much slower than normal.

    So i am still convinced headaches come from dehydration. And whether or not electrolyte imbalances are involved is another matter. I thought at they first it possible but now i think its just standard dehydration and no electrolyte problem. Still doesn’t hurt to increase salt intake though as this makes you drink a bit more water and helps you retain the water in your body.

    Hi Pattience, try this link

    I think this is a good explanation of the ideas and it doesn’t try to sell the concept or sell anything else–just explains the state of knowledge as it is (or as it was when it was written).

    What I mean by up-regulate here is that all cells have systems to “clean house” and repair damage and these systems can be turned up or down or even off completely. Nearly everything in a cell is composed of protein and a protein is a folded long chain of amino acids. So making repairs and cleaning up a cell or killing off a sick cell results in amino acids being available for re-use, the same as if you eat a meal of protein. So it makes sense that if you are lacking in protein in your diet, the body will use hormones to increase the process of repair and housecleaning in order to get the amino acids that it needs. Housecleaning and repair in cells goes on all of the time, and it’s known that it is regulated by hormones. It also makes sense that since the body needs stored amino acids in case of dietary shortage, it might delay serious cleaning until a shortage actually happens. A system like that would work for people who regularly faced such shortages.

    The body has no dedicated storage for protein like it does for fat. The body can use fat exclusively for energy but it can’t make protein from fat. The whole body itself functions as amino acid storage. When the body needs amino acids, it doesn’t make sense that it would just randomly start breaking down muscle to get them, but instead will spend more energy to do more repairs and housecleaning. If you’re short of food you’ll need that muscle, and everything else that’s in good condition, in order to get food, so healthy tissue will be the last place the body goes to.

    Alzheimer’s is thought to be caused by accumulations of a mis-folded protein called beta-amaloyd. And there’s another mis-folded protein associated with Alzheimer’s called Tau. Mis-folded proteins aren’t uncommon but they normally are recycled and don’t accumulate and it’s not know why that doesn’t happen with beta-amalyoid. The idea here is that increasing the level of housecleaning, or maybe turning on a system that simply doesn’t operate when there’s plenty of amino acids available, will work to reduce the accumulation.

    Up-regulating this house cleaning and repair could also potentially nip cancer cells in the bud. But it’s all very pioneering and theoretical. The body is amazingly complex and while what we know is pretty amazing, there’s still vast unknown physiology. But I don’t eat protein on fast days because this idea fits my picture of how the body works. People tend to translate loss of “lean tissue” which really means “other than fat” to loss of muscle when it could really be many other tissues. And loss of lean tissue, even if it’s muscle, isn’t necessarily bad if it’s damaged tissue. So I’m unconvinced by arguments that I need to eat protein every day to maintain muscle.

    I don’t get headaches myself but I would guess that any change in routine could cause them and it’s possible that some people might be sensitive to protein foods or lack of them. I’m sure that if I thought I needed to eat eggs to avoid a headache that’s what I’d do. I might try to de-sensitize myself by gradually going off protein on fast days, but I recognize that if the pain is severe, this might not be realistic.

    Thanks for your interest.

    Great post, thanks!

    Does anyone know if adding some BCAA`s to water through the fasting days, is a good or bad thing.

    If you don’t eat enough protein on your fasting days your body will lost to get the energy and nutation.

    Yeah you must take Proteins on fating days. Proteins are essential to build up the muscles and if muscle building is the purpose then you must take proteins even on fasting days.

    Soya or whey that actually depends on you. But preference will be given to Whey protein.

    For expert review you may visit:


    Im starting with whey on training days, considering fasting days. Even though my fasts are 16-24hrs and I should not lose muscle.

    You may want to watch the linked video – Dr Fung talking about the basics of fasting. He discusses many “myths” associated with fasting. Quote below – during the video he talks about one person who fasted for a year. Guess what – he didn’t lose muscle mass!

    Breaking Down Myths About Fasting

    One common myth is that fasting will lead to loss of muscle mass. The book clearly describes the process of protein catabolism, explaining how your body actually downregulates protein catabolism and upregulates growth hormones in response to fasting.

    “If you follow the biochemistry, your body stores energy as glycogen in the liver, which is links or chains of sugar, and then it stores [it as] body fat.

    During fasting, you start by burning off all the glycogen in the liver, which is all the sugar. There’s a point there where some of the excess amino acids in your body need to get burnt as well.

    That’s where people say, ‘That’s where you’re burning muscle.’ That’s not actually what happens. The body never upregulates its protein catabolism. Never is it burning muscle; there’s a normal turnover that goes on.

    There is a certain amount of protein that you need for a regular turnover. When you start fasting, that starts to go down and then fat oxidation goes way up. In essence, what you’ve done is you switched over from burning sugar to burning fat. Once you start burning fat, there’s almost an unlimited amount of calories there. You could go for days and days.

    What’s interesting is that if you take a pound of fat, that’s roughly 3,500 calories. If you eat somewhere around 1,800 to 2,000 calories a day, it takes two full days of fasting to burn a single pound of fat, which is very surprising to people. If you’re trying to lose 100 pounds, you could theoretically go 200 days of fasting just to burn all that fat … People worry about fasting for 24 hours. I’m like, ‘You could go 200 days.’ Then it’s like, ‘OK. Maybe it’s OK to go 24 hours without eating.'”

    Thanks I did some weight training 3 hours after breaking my fast so I took whey afterwards. If no weight training I would eat meals as usual no whey. I will continue as planned.

    I like to eat 1/4 TDEE on fast days to keep some energy and drive safe.
    Example: 16hr fast to FD (one meal) 19hr fast to NFD. x2 per week.

    Maybe I will try extended fasting in the summer.

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