Effect of 5:2 on gut bacteria?

This topic contains 31 replies, has 14 voices, and was last updated by  LJoyce 1 week, 1 day ago.

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  • Every other day, it seems, there’s more and more fascinating information on the human microbiome and what it does – even if researchers aren’t always sure how it does certain things, or what exactly constitutes a “good” microbiome. I’m not holding out hope that one day I’ll be able get a christensenella implant (what I call the “garbage guts” bacteria, common to those horrible people who can eat vast amounts of anything, including junk food, and remain thin), and I’m not going to get maniacal about it, but I’m all for getting a happy and diverse bunch of bacteria in my gut doing what they need to do. For now, I’m happy to do things like open a window, get into the garden, eat as big a variety of plants as I can (experts say aiming for 30-40 a week, minimum, is the way to go), and have something fermented once a day.

    Now I’m wondering: does IF impact the bacteria in any way?

    Do they recuperate in the downtime, like the rest of the body does when fasting, or does fasting cause bacteria population to drop? Or neither? I’ve also read that while a high fibre diet is very important for the bacteria, it only seems to “work” when you are consuming high fibre (that’s 30g and up) every single day – no days off. This is impossible to do on 5:2 unless you’re taking fibre supplements, and no, I’m not keen.

    Thoughts? There’s very, very little information about IF and the microbiome out there – at least out in Google, where the non-scientific plebs like me hang out – and I’m hoping that some of you well-informed ones might be able to shed a little light on the subject. (Note, however, that I’m not looking for an excuse to go off 5:2 even if it’s not ideal for the bugs in my tum. It’s just been too good for me. I’m just after extra information.)

    Thanks! I look forward to your replies.

    That’s a very interesting question and I wonder along with you but, alas!, I’m not a scientist of any variety so I have nothing definitive to add.

    For myself, I take a probiotic supplement in the hope that will help promote a healthy colony of gut flora.

    Ah – no scientists required for answering this question. Just people more informed than I! πŸ™‚

    Probiotics are good, but the research that is coming out suggests that their benefits have been overestimated. Prebiotics (ie. foods that bacteria in the gut can feed on – usually high in fibre) appear to be more important. And, of course, a variety of plant foods, for a wide variety of bacteria.

    There is a lot of intensive research on this going on but the people doing it are keeping there findings very close to their chests, because if they can isolate the right bacteria and make a pharmaceutical out of it there is big big big money to be made under the label “A cure for obesity”.

    I wish some of the questions on this forum could be passed on to microbiologists willing to reply.

    I am watching this research with interest too. In the meantime I usually have 100g of symbiotic yoghurt on a FD which really fills me up. Also make sure I have some red wine on nonFD’s too as I read somewhere that this is great for gut bacteria😊.

    Ooh! The thread is alive again! Yay!

    Vero, what I’ve read so far is that they don’t want to say what constitutes a good microbiome. For example, one of the bugs they’ve isolated is christensenella: that could definitely be the “cure for obesity” you mention! But at the same time, christensenella may allow you to eat whatever you like without gaining weight, but it doesn’t guarantee overall health. So yeah. I’m not discounting that they’re waiting until they can make money from it, but I also think it’s early days and there’s not that much to tell.

    Jilly, I hadn’t read about the red wine! I’m a teetotaller but I know several people that’s going to make very happy. πŸ™‚ I’m eating a high fibre diet and striving to eat 30-40 different types of plant matter a week. I also have something fermented every day. I ferment my own veg (either as kimchi, or in milder lactofermented form) and either have a bit of that, or some miso soup, or some yoghurt. It’s pretty easy, and enjoyable.

    Still wondering about the effects that fasting has, though. The bacteria appear to react quite dramatically to sudden dietary change: I recently read a study that the weekend junk food binge (ie. three days) can decimate gut bacteria and undo all your nurturing of them through the week. But fasting isn’t the same as going nuts on junk food, is it?

    Hmmm… let’s see if someone else can enlighten us!

    A new enzyme has been discovered in leafy green vegetables particularly spinach. It is suspected to have properties to improve gut flora and possibly act as a probiotic and even antibiotic.


    Fascinating! Thank you! I love my green leafy veg. πŸ™‚

    It really is an interesting field!

    Perhaps you’re aware of the experiments in fecal donation. That ongoing research involves taking fecal matter (ugh!) from thin people with healthy metabolisms and inserting it (more ugh!) into people with various health issues that are suspected to be based on unhealthy metabolisms. Scientists are asking the question can people “catch” healthy like they “catch” disease (YIPPEE!) when their intestinal flora is properly balanced.

    The way I see it, intermittent fasting may have the potential to accomplish a similar thing without the transfer of fecal matter. When we give our digestive systems some down time we may be changing our own intestinal flora.

    I know that it’s been about 9 weeks for me. In that time I have done 2 back-to-back fasts of just water each week. The totally remarkable result for me is that my appetite for food has changed in a very fundamental way. I enjoy the food I eat on my food days but, most surprisingly, I am not hounded by cravings that have plagued my 68 year life. I have very little difficulty resisting foods that are counter productive for me. For the first time in my life I feel like I actually have a *choice* as opposed to a *compulsion* about what to eat and what not to eat. It is a small miracle in my life and it feels like it’s *happening* to me rather than being a monumental struggle to master obsession.

    I’m guessing that’s about gut flora far more than it is about anything I’m consciously doing. I’m also sure, in a totally anecdotal way, that it has a tremendous amount to do with lots of veggies — leafy and more substantial — and a nearly complete avoidance of sugar and starchy carbs — in my case, including all grains.

    I look forward to what this area of research makes more clear over time.

    Hi Chubster,

    I am relieved to hear that intermittent fasting might be an alternative to fecal transfer! It seems infinitely preferable to me.
    Today is Monday so I am on my fast day. Just celery soup and a plain yoghurt. I like vegetables so it is no trouble eating those on other days too. Keep up your fecal chronicle. It is interesting.

    AMEN! MUCH better to effect this change in the gut ecosystem with veggies! πŸ˜‚

    There is an amazing book published in 1910 about how fasting cures many ailments written by Upton Sinclair, and although he had no idea why fasting seemed to work so well, I would guess that the reason was because the gut microbiota changed during the fast. He only fasted longer than 3 days, because he said that it was a waste because 3 days were the time that hunger was present, but he said that if someone was too heavy, or too skinny, the fasting seemed to ultimately reset their body weight to their ideal body weight naturally after the fast, although the focus in the book was on a lot of other benefit to fasting. The book is free now, and easy to find it as a pdf on google because it is out of copywrite. It’s called the fasting cure.

    If I had to guess though, I’d guess that fasting had some sort of profound effect on the gut microbiota. And probably intermittent fasting would have the same effect, especially if a person was eating standard American diet. (SAD)

    I’ve been diagnosed with SIBO (small intestinal bacteria overgrowth). There are only supposed to be small amounts of bacteria in the small intestine; they’re supposed to be mostly in the colon. There are many possible causes, including food poisoning, heartburn medications, etc.

    I read a book about it and was surprised to learn that the small intestine has cleansing waves to wash bacteria down into the colon between meals. But it can only happen after 2 or more hours of no food. The book does not recommend fasting per se but advises 3 meals a day with no snacking. I get the feeling that fasting causes an even more deep cleansing than 4 hours between meals.

    I know that my gut feels more clean when I’m fasting, and my IBS symptoms like cramps, bloating and gas go away. They return on my feeding days however, so the effect isn’t permanent. But it does make me look forward to fasting just to be free of pain and “reset” my gut.

    Anyway, here’s an interesting blog about the microbiome. This guy went lived in Africa for a while to try to diversify his gut biome. He links to studies in which they are trying to run studies of gut bacteria from as many people as possible. They have an American project and a British project. You can send in a sample (ahem) and they will let you know how your gut compares to others.


    British gut – https://fundrazr.com/campaigns/4sSf3/ab/5qJ7f

    Hi Lemna,
    yes, that was a very interesting article about that guy going to Africa. I’d do the same thing if I had the money and time for that. I think that he’s doing the right thing.

    Interesting article on fermented food benefits (microbiome) :


    Recent episode of “Trust Me I’m a Doctor” looked at pro-biotics, sort of. They discussed the merits of them but opted to do a trial of eating oatmeal every day for 6 weeks (porridge, muesli, etc, as long as the eater got 3 tablespoons of oats). DNA of gut bacteria analysed at start & finish. At end of trial the DNA of bacteria known to be beneficial to heart health & protect the linings of the intestines had the strongest signatures – they were present at start of trial but very weak.
    Good news for me as I have been eating oatmeal (rolled oats so unprocessed) for years as a method to reduce cholesterol levels (3 tablespoons rolled oats so unprocessed). I only add a bit of fruit & flax seeds so low in calories (under 200 calories according to the app I use). Occasionally add roasted rolled oats to Greek yogurt as a snack on days I don’t have porridge.

    This site seems to have gone quiet, but it still seems the best place to pose my question. Over the last few years I have lost a lot of weight with 5:2, which I am now combining with limited time eating. However, in the last 18 months I have had two colonoscopies and a length of my colon removed, all of which required my gut to be thoroughly empty. I am assuming that along with every thing else, my friendly bugs went as well. So, without going to Africa, how do I get them back? Until a couple of weeks ago, when I started limited time, I ate rolled oats and I still have Greek Yoghurt. I eat a reasonably wide variety of fruit and veg ,so I may have recovered some, but how do I get more? If possible I would prefer an answer that didn’t involve buying something with the word “biotics” on the side. Next week I intend to start making Kefir, about which I have heard good reports. Any feedback about that would be useful.

    Eat fermented foods. Fermented soya milk. Eat raw veggies, don’t peel them (Id even wash the veggies sparingly). Eat whole fruit with the skin on. Natural Greek yogurt. Avoid sugar. Eat lots of soluble fibre, beans, apples. Green unripened bananas.

    Thanks bigbooty. Apart from soya milk and green bananas I am pretty much there. I am happy to eat the veg I grow unwashed and unpeeled. Soya milk will be a challenge. I went off it 50 years ago when I lived in Hong Kong -it was all we could get and it was vile. I eat a banana most days but have never eaten them green. I’ll give it a go.

    So far I have not seen fermented soya milk. However, we have a strong Polish community in this area and the local supermarket has started to stock Kefir at a very reasonable price. I have just tried my first glass (about 1230pm, I don’t do breakfast). My reading on the subject suggests that this is a very healthy thing to drink and I also found it very much to my liking. The next step is to start making my own.

    Hello Betty’s girl,

    Going back to your original post, you may find this video interesting. In it Tim Spector, from Kings College, talks extensively about gut microbiobe; touching also on the issue of fasting and it’s effect on gut flora.


    Fasting just increases akkermansia bacteria that feeds from the mucus in your gut and protects it. There are only benefits from fasting unless you are in poor health

    There is a very good book on this subject that I heard about on this forum, “10% Human” by a researcher, Alana Collen. https://www.amazon.com/10-Human-Microbes-Health-Happiness/dp/0062345990/ref=sr_1_1?ie=UTF8&qid=1502467020&sr=8-1&keywords=10%25+Human



    I’m only about halfway through it, but it’s completely fascinating.

    One thing to keep in mind about eating fermented foods is that most of what you buy in a supermarket has most of the good bacteria killed off by heating it. Sauerkraut for example, is filled with helpful strains of good things for your gut. But it would continue to ferment in the can and probably explode it if they didn’t use heat to kill most of it off. Things like yogurt and kefir are the same. These are all easy to ferment on your own at home and are full of probiotics. It’s also much more economical to do your own.

    Also very good is “The Diet Myth” by Tim Spector.

    CalifDreamer – I have just finished a home-made leek and bacon quiche with shop bought sauerkraut and pickled veg. I’m hoping some of those bugs survived! At least the evening kefir will be my own.

    Penguin, I think you may have killed off some of the strains just by cooking it, but that doesn’t mean it isn’t a good tasting dish! The cabbage is still a heathy cruciferous vegetable. I often make sauerkraut and bratwurst cooked together. It just doesn’t taste the same with lukewarm sauerkraut.

    Penguin, I just started a big jar of goat milk fermenting. I did keep some of the grains in cow’s milk too, just in case. I rinsed off the grains that I put in the goat milk. Our water is pretty good here, so I just ran it under the tap water. I can’t remember if I did that last time I switched grains from cow to goat, but I do rinse them occasionally even when not switching. I’m being overrun with kefir! Good thing it keeps in the frig, both grains and finished.

    I have been avoiding kefir on FDs because I’m not sure of the calorie content and I’m pretty good at counting everything. At first I was using the unfermented milk measurement, but then penguin pointed out a possible lower count because of the lactose being eaten by the grains. Has anyone come up with a good count? I suppose it varies by how long it’s been fermenting and I shouldn’t be so anal about calories. 😁

    CalifDreamer. I didn’t cook either the sauerkraut or the pickled veg – ate them as a cold side. I’m getting to like them. When they are gone I will make my own – the garden is full of veg I need to do something with.

    The creamy kefir worked well – thicker and a good taste. I had intended to revert to either straight full milk or goats milk, but I had a tub of single cream going spare, so the batch currently fermenting is half cream and half full milk. Looking good. The kefir grains are now getting very plentiful – not overrun yet but getting there, they really seem to like cream.

    My weight is plateauing at my initial target but I ‘ll have a fast day tomorrow. For me FDs are usually zero cal and black coffee/green tea so the cals are not a problem if I allow myself what has become my mid-evevning habit of a glass of kefir.

    I used the nutrition panel on the kefir that I purchased as a guide to calorie count. The brand I bought was made from full fat organic non-homogonised cows milk and it says that this is 99.7% of the product. I figured if I made kefir from whole cows milk it would have a similar calorie count once fermented.

    Full fat cows milk contains 62-65 calories per 100ml, depending on brand. But the kefir I purchased contains 48 calories per 100ml. I don’t know why this happens, but I assumed the difference was due to the fermentation process as the lactose (milk sugars) are the food that the kefir grains eat during fermentation.

    I have been having kefir on FDs. Never more than 100ml and sometimes a little less if calories are tight.

    LJoyce, you know the confusing part of that is that the original full fat milk is still there, even if fermented. So where do the original calories go? You didn’t remove anything. (If, in fact you fermented it yourself) So do you go by the milk calories or the kefir calories? I suppose this is all kind of a moot point since calorie listings are at best an educated estimate on most food products. I guess I would go by the original milk calories unless I learn of a reason not to.

    Penguin, if you like sauerkraut, you must try fermenting some yourself! No staters needed, just cabbage, non-iodized salt and a jar or other vessel to ferment it in. It’s SO much better than the stuff from a can.

    Cali, Where did the calories go? I am not a food scientist, but this is what I think:
    There are a number of processes that change the nutrition in a food so I know it’s possible for a food to lose calories through a transformative process.
    For example sprouting legumes reduces the calories. I assume this because the bean/pea/lentil uses some of the stored energy to fuel the sprouting process.

    As for kefir, the only logical thing I can think of, is that some of the lactose is used by the kefir grains to multiply the bacteria and grow more grains and some is expelled as gas as part of that fermenting process. One of the things that leads me to believe this is by comparing the differences in the nutrition panel on a bottle of full cream milk and a bottle of kefir made from full cream milk. There is very little difference in the fat and protein content on both bottles. The main difference is in calories, carbs and sugars. Per 100ml, the kefir has 60kj (14cal) less than the milk and the carbs and sugar have more than halved. Both carb and sugar in the milk is 4.5g per 100ml and they are both 2.2g in the kefir.

    I could be completely on the wrong track with my thinking, I’m just trying to find an explanation for a calorie difference where you start with the same food and don’t personally remove anything. My brain does is usual thing of trying to come up with logical explanations – some of which have the definite potential to lead me up a few dead ends.

    LJoyce, that sounds completely reasonable. I wasn’t thinking of the gases expelled while the milk is fermenting, but that does happen. And the new grains that are produced are removed from the finished kefir. It’s definitely a different product than what you started with. I bet baking bread changes the calorie content of bread dough. If nothing else, the evaporation of liquids when baking would make a difference.

    Cali – This 2 things that led my thinking down that path were: the fairly recent articles that I’d read on how the human body burns energy and what is expelled on our breath; and wikipedia says that the kefir grains are made from celulose (which I think is a carbohydrate that is indigestible to humans).

    The real problem with my very logical brain is that it can reach what looks like a perfectly reasonable conclusion, but because I have no background in the field I can quite easily be making incorrect assumptions. That’s one of the reasons I’m always wary of the bulk of info on the internet – I assume that there are plenty of others out there who make the same leaps of logic and don’t necessarily land on an answer that’s accurate.

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