Food for Thought on a Fast Day – Will intermittent fasting cause you to faint?

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Food for Thought on a Fast Day – Will intermittent fasting cause you to faint?

This topic contains 30 replies, has 20 voices, and was last updated by  maysi01 8 years, 4 months ago.

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  • Over the next few weeks, we’ll be posting  10 myths about dieting from the article by Michael Mosley in The Times

    Claim 6.  If you stop eating for a while then your blood sugar will fall dramatically and you will faint.

    In the trial I mentioned in the previous postResting energy expenditure in short-term starvation, they also measured the volunteers’ blood glucose levels. They found that their blood glucose levels did slowly fall over the three days, from 4.9mmols/l on day one to 3.5mmols/l  by day 4.  These, however, are the sort of levels you might expect to see in a healthy individual who had their blood taken before breakfast . They are not, in any sense, abnormally low.

    At the same time the levels of fatty acids in their blood shot up, showing that their bodies had switched into major fat burning mode.

    Your body evolved to cope with periods without food. Modern humans, however, are used to eating lots of regular meals and there is evidence that the hunger hormone, ghrelin, rises simply in anticipation of a meal. Intermittent fasting can be tough, but there is no evidence it is will cause you to faint.

    Thank you for addressing this one. I’ve had several people worry at me over how they couldn’t possibly do 5:2 because they’d feel too weak and faint. They seem to think I’m superhuman somehow for regularly going 20+ hours without eating or drinking anything other than water.

    I know a lot of people new to 5:2 do experience odd symptoms like that, or headaches and I did have a couple of crazy headaches myself early on but I’m sure that’s more ‘withdrawal’ from caffein or sugar or carbs, or just our bodies adjusting to the new WOE. I’ve certainly never felt stronger or more clearheaded than I now do on 5:2. I’ve had my blood sugar checked twice in the last few months (both after a long fast period) and they’ve been ‘perfect’ apparently.

    The reason blood glucose levels, and exergy levels are all over the place is predominantly due to the food people eat these days. Processed cereal grains, food that has little nutritional value.

    The concept of eating carbs for breakfast every day of your life is lunacy. Blood sugar spike, insulin release to manage plasma glucose levels, blood sugar drops, you feel tired and grumpy, eat something carby mid-morning ,and the cycle continues.

    If people were to eat more of a protein and fat based breakfast, this rollercoaster would end after a few days. No-one mentions that er?

    I agree with Micheal wholeheartedly, we are creating this problem for ourselves, but no-one knows how to eat any more, so no end is in sight 🙁

    I agree with Stephen. On the 5 days I have porridge with fresh fruit mainly because I love it. On Fast days I have an egg based meal and can go all day without any hunger pangs or faintness. This is not the case on the 5 days so I am reluctantly going to switch to having more protein at breakfast. The diet is just wonderful. I have lost 3 stones since January and dropped 3 dress sizes.

    I am a believer in protein for breakfast. I slice a scallion shallot (the big one) and then fry it in a little oil. At the same time I beat two eggs and add a little soy sauce before pouring it on the partly fried shallots. It is delicious and keeps me going for hours.

    Can anyone help me? I am type 2 diabetic and take 2 metformin per day. Dr. Michael’s book says don’t do it if you are type 1 but as far as I can see, he doesn’t mention type 2. I discussed it with my GP who said that he thought it was not a good idea to do 5:2 which is a pity because I have purchased both books, read them and are raring to go.


    They are using intermittent fasting along with dietary changes to cure type 2 – this may explain:

    Good Luck!

    I am not a Type 2 diabetic, but there are folks managing type 2 diabetes just fine. Eventually, you may need to reduce your metformin.

    It seems your GP would be in favor of you losing weight.

    Davis, I am type II diabetic and fast regularly.

    I had my HbA1c checked before I started because I wanted to know what happens and it turned out to be quite high. My diabetic nurse wanted me to start on Metformin which I took for two or three weeks and then stopped.
    Three months into fasting my HbA1c had gone down to “well controlled”, no Metformin, but occasional cookies or ice cream.

    If you are on medication, in particular insulin or those that cause further insulin release by your body such as sulfonylureas (Gliclazide, Glibenclamide etc.) you need to monitor your insulin levels carefully to avoid hypos. It would probably be best if you could find a dietitian or diabetologist to support your fasting in that case.

    I will agree with what Michaelis sayIing as true to my experience not only for intermittent fasting but most calorie restictio. Diets ive tried.

    At first I struggle and have even get the shakes on otger diets. But after a month feel as im conditioned to missing meals, and struggle less.

    agree with drummerchen too.

    Thank you to those who responded to my question about Type 2 diabetes and 5:2. I shall be seeing my diabetic nurse tomorrow, Friday, and I shall discuss it with her. It seems to me that if I reduce my Metformin to one per day and take it with the one meal then I might be OK. Any comments?
    It’s nice to know you are out there, people!

    David, do you check your blood sugar levels? If not ask the diabetic nurse tomorrow for a glucose meter and test strips and then you can check how your blood sugars are. Check with the nurse when and how to reduce your medication based on your blood sugars.

    Without knowing your diabetes it is impossible to give individual advice, I’m afraid.

    Dummerchen, thank you. I am afraid I don’t check my blood sugar levels as I didn’t think type2’s needed to. I have a blood glucose monitoring machine but didn’t think I needed to use it. It would appear that I might have been a bit unwise from what you say. I shall discuss it with the nurse tomorrow and report back for further valued comment if you don’t mind.

    I urge you to join a diabetes forum. There you may find not just alot of info , but some life long friends. Hopefully some long life friends.

    im not expert enough to point to anything, but the group im with keepeachother on the straight a narrow.
    Very little room for denial. And denial of diabetes and care there of can make a major difference in the quality of life. Rule of thumb. Get with a group as knowelgble as your doctor. Might as well make the best of it eh?

    start walking fitness if possible

    best wishes

    Hi David. I am not diabetic but like some on this forum over the past year have read some very good research done by people who have type2 and are doing the 5:2 lifestyle. Up in the North East of England researchers at Newcastle University have developed a very strict low calorie diet regime which they say shows that several weeks of daily low cal intake can have a dramatic effect on type2. Google “The Newcastle Diet” to get the info. Also go to the Diabetes UK website where you will find info on this diet and lots of helpful info.
    Good luck.

    Diabetes UK do not support or promote IF. Instead they continue to promote a low fat, starch based diet – after all, us diabetics cannot metabolise carbohydrates well, therefore we need to base our diet on plenty of carbohydrates.

    “Dietary management of diabetes depends more on eating regularly and including starchy carbohydrate foods like pasta at meals,…”
    Six small, starch based meals, the opposite of IF and no longer in line with newer research.

    Whilst I can see the excellent idea of the 5:2 it’s a bit difficult to do it when your other half is already at ideal weight and doesn’t need to fast. I have formed a slimming club which is based on something Michael said in an earlier broadcast on BBC2. He cupped his hands and said that we ought not to eat more at a meal than could be held in the hands. This gave me the initial idea that instead of cupped hands (he didn’t mean it literally) I used a nine inch plate. I lost 2.5 stones in six months by sticking strictly to the plate and cutting out anything to do with sugar. I lecture to mainly middle aged people and I give them three talks, one on the diet, one on using walking to get fit and the other one on Psycho-Cybernetics which is the use of mental imaging and your subconscious to condition the brain for going for the weight loss target. The club has proved highly successful and I am fortunate in that my local surgery lets me use their lecture room free of charge on the Saturday mornings on which the surgery is open anyway. This allows me to give the service entirely free of charge.
    “If you can’t get it on the plate, you don’t eat it”. No seconds, and don’t pile it up. You soon get used to the amount.
    Best wishes

    A while back I looked into Bariatric surgery, not for myself but because it seemed an interesting field to work in. The claim is regularly made by those in favour of gastrectomy that patients with Type II Diabetes frequently leave the hospital with normal and stable blood sugar levels – and this is LONG before significant weight is lost.

    So my conclusion is, if you can normalise your blood sugar and lose weight without having to undergo this terrible, irreversible procedure, then surely this is the better way to go. Bariatric will condemn you to a lifetime of meal planning and food obsession…you’ll lose weight all right but at what cost??

    Yet pro-bariatric doctors don’t tell people that their Type II Diabetes is a reason to avoid Bariatric surgery, quite the reverse.

    Basically, bariatic surgery condemns the patient to a life of perpetual fasting. Unless of course the patient figures out how to liquidize a lot of the high calorie sugar and fat bombs and then gains weight again; not uncommon after such surgery.

    I for once continue to intermittently fast voluntarily. It seems the healthier and less dangerous option.

    I am about to embark on the 5:2 but have mild hypoglycemia. I am concerned that on the fast days my sugars will drop and i will feel very tired and shaky. Anyone ?


    Be vigilant about being in contact with your doctor. . Before during and after fasting. It seems a big danger is fasting while on medications that aren’t able balance , rather experiencing high or low sugar reactions. Where certain medications can make fasting a danger. I believe there has been a lot of change in the pharma industry to use Meds that wont cause life threatening conditions as they were in the 1990s . However it’s best to approach the weight loss with you’re doctor on the same page. iykwim .

    With that said. Choose carbs that trickle rather than gush.

    Sometime ago I did some research on metformin, and was surprised to find a study that found that type 2 diabetics that take metformin have a lower chance of contracting cancer, normally diabetics have a greater chance of contracting cancer than non diabetics, but those on metformin had a slightly lower cancer rate than even non-diabetics.
    So for that reason alone I would not be in a hurry to stop taking it.
    Google “metformin reduced cancer risk”

    Regards Stuart
    This is also a good know page of Info, and is simple and quick to read.

    Those of you who are type 2 diabetic and worried about fasting – have a look at this website . A Canadian nephrologist who got fed up being sent type 2 diabetics with kidney problems because he couldn’t do anything for them – unless he could reduce their blood sugar levels. So he started looking and concluded that type 2 diabetes is a hormonal problem that needs a dietary cure so devised his dietary regime. His method also includes fasting (up to 36 hours). He has recorded several lectures which are worth watching but the information is also there in his blog. Lots of scientific evidence quoted and also lots of case studies of people he has treated (put on his dietary regime!). For those who don’t have T2D the calories and exercise blog entries are really worth reading as well.

    thnks stephen it`s help me a lot

    thanks jimitech for thus link. i will checked out

    Jlmitch thanks so much for the link. I watched the videos and its pretty incredible. Very impressed and very excited to try fasting for weight loss as I am 51 and considered obese. The only thing that I question is whether they studied women of various ages (I.e. below 50 and over 50 and menopausal). Overall, extremely encouraging!

    Davidalf “Can anyone help me? I am type 2 diabetic and take 2 metformin per day. Dr. Michael’s book says don’t do it if you are type 1 but as far as I can see, he doesn’t mention type 2. I discussed it with my GP who said that he thought it was not a good idea to do 5:2 which is a pity because I have purchased both books, read them and are raring to go.”

    David I was diagnosed with type 2 diabetes about ten years ago…I no longer take metformin and currently control my blood sugar level entirely with my food choices.

    I had to step past the advice given by diqabetes organizations and dieticians, because it was looking like making my problem a lot worse.

    I am not a very healthy woman but I don’t need to take diabetes medications anymore thankfully…this allows me to start working through the layers that underlay the problem.

    Of course, reducing the waist measurement is a major move in the right direction, anything that supports that is a help.

    Good luck.

    I’m hoping someone will be able to give some advise/help… Everything I’ve read on the 5:2 diet says that you will feel hungry but never faint, however when I have attempted to reduce my calorie intake I feel like I go past the hungry stage, I feel dizzy, faint and sick, so much so that I end up on the floor of the bathroom pale and shaking and this doesn’t go until I have something to eat. Before I had my daughter (she is 2) I never had this issue but now I can’t seem to cope. Recently I have attempted (and failed!) to fast, first meal of the day either at breakfast time or lunch time consisting of porridge or a hearty soup, if I only have 1 meal before dinner time I get to about 3-3:30 until the fainting symptoms appear. Can anyone give me some idea of how to get past this as I really feel like 5:2 is the diet for me if only I can get onto the fasting days!!
    Thanks in advance

    I would definitely see a doctor as this seems unusual regardless of which diet your on.
    Not advice as I’m not a professional and may not give advice… Try going on probiotics for six weeks so it will help to break down what foods you do consume. And plenty of water or green tea with lemon.

    Avoid other foods with caffiene in them ie diet soda. To see if if that’s lending to the shaky feelings.
    Best wishes.

    I agree with SAMM, see your doctor as it is better to be safe than sorry.
    Also take a look at what you are eating the day before. If you eat a lot of processed carbs and sugar and then fast the next day, your blood glucose will plummet which would make you feel faint and unwell.
    If you do eat a diet high in such things, maybe you should spend a couple of weeks cutting them down and introducing healthier food before trying to fast.
    Good luck.

    My 2c on this topic. I have posted in the Type 1 Diabetes thread a few times, and am perusing other threads today. I fainted for the first time in 20 years during a fluorescein retinal scan on my second consecutive fasting day. As a Type 1 diabetic I am very familiar and comfortable with venipuncture, but on this occasion the inexperienced tech failed twice to get an elbow vein and then blew a vein in the back of my hand. At this point, although consciously not panicked – in fact I was reassuring her, I managed to have a deep syncope with minor convulsions. I believe the main cause of the severity was the staff keeping me in a seated position (idiots!) rather than getting me flat. This was on my second fasting day, but my blood sugar was NOT at all low (6.something mmol/l, measured immediately after the event). I can see that various elements of physiology are changed by fasting (why else do it?), and it is POSSIBLE that on the second (consecutive) fasting day, with things farthest from normal, that I am more prone to vasovagal syncope (simplistically I think of this as fainting caused by the brain). It is possible that this can be somewhat generalised to others, and unless you have a reason to have a medical procedure on a second consecutive fasting day, there is a small incentive not to do so.


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