Dizzy after first fast day

This topic contains 7 replies, has 7 voices, and was last updated by  dykask 4 years, 1 month ago.

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  • My first fast seemed pretty easy. Two meals, black coffee, water, possibly slightly under 500cals. I felt briefly dizzy during the day but it passed quickly.

    Woke this morning ravenously hungry and distinctly dizzy. Have eaten and hydrated and still feel dizzy. I’m noT falling over but my head feels swimmy.

    Not giving up but is this common? I’m 61 and have a BMI of 31 but otherwise healthy, is there anything I should do or not do?



    Feeling dizzy is a sign of dehydration and the fact you felt it the following morning suggests it’s the issue.
    Drink more water on fast days, we get 90% of the water we need from our food and if you feel dizzy take a pinch of salt with a glass of water. It has always worked for me and I know there are many other fasters who use the pinch of salt trick.

    As for feeling ravenously hungry, it takes your body a while to get used to having so few calories but it does help if you keep the carbs down on fast days and concentrate on lean protein and vegetables.

    Good luck and let us know how you get on.

    I still seem to get that the day after a fast in the morning. In fact one dizzy spell just ended which prompted me to come here to see if anyone else had the same thing!

    It is starting to worry me, as I don’t think an otherwise healthy person should react this badly to a measley 1 day fast! I’m 29, 5ft4 and float around 9st but want to get to 8st5.

    Around 10 mins after I got up this morning, I started getting really really hot (sweat becoming visible on my forehead) and I knew what was coming. I managed to grab a bowl of cereal for carbs before collapsing on the sofa. I lay there for ten minutes before trying to lift the spoon to my head, dripping in sweat all the while. I got half the bowl down me and lay down, and I was totally back to normal around 10 mins later.

    It’s strange, feeling one minute like you’re totally helpless and not long after feeling right as rain.. sugar always sorts it, I tried a protein shake once and was sick almost immediately.

    I was wondering if anyone else gets this, as if not I want to look into my blood sugar regulation is not so strong..


    It sounds like low blood sugar (hypoglycaemia) to me.

    It might be worth reading up about the Glycaemic index, this is a good explainer: https://www.health.qld.gov.au/__data/assets/pdf_file/0026/143567/paeds_gi.pdf

    Eating foods with a low GI through your fast day, should make a difference. Several small, low GI, serves during the day with one just before bedtime, and one when you first get up in the morning.

    It may also be important for a doctor to check you out.

    It can be part of what’s known as “keto flu” When you’re body is using up your stored sugars before your body moves into ketosis (switching to burning fat for energy) It passes once you move fully into ketosis. I’ve found that I get it every time I’m fasting after eating too much sugar/starch and it lasts about 2-3 days.

    I felt dizzy when I started the 5:2 on two separate occasions. Also sweaty and light headed.
    I’d love to know what caused it but on both occasions I had an apple and then I felt fine.

    That was in the first week. I’m in the third week now and things seem to be fine.

    Thanks for the replies!

    I normally eat nothing at all on my fast days, just lots of water tea and coffee, as I feel hunger less that way and find it much easier.

    I will start considering having a small thing in the evening to stabilise my blood sugar in the morning, it’s just frustrating that I can’t do the pure fast that I prefer to do, but the body wants what it wants I guess!

    I will look into the GI ratings of my food, because before my last fast I had spent the weekend in Italy really loading up on the pasta, which probably didn’t help matters considering I was leaping from that to no food at all.. pretty silly really.

    My dad does 5:2 too and is totally fine no matter how strict he is with it. Maybe starting weight has something to do with it?

    All the best to anyone fasting today!

    For about 2 years I would feel dizzy around 22 hours into a fast. When ever I was checking it was when my blood glucose when lower than normal. (Blood glucose isn’t hard to monitor.) Over time that faded and rarely happens. The dizzy period would last for about 90 minutes. I normally only water fast.

    Last month it happened during a five day fast, when I checked my blood glucose was down to about 2/3rds normal. Later I wasn’t dizzy and my blood glucose was even lower, indicating I was probably in ketosis at that point and my brain wasn’t missing the glucose as much as it was earlier.

    Still not all reasons for feeling dizzy are so simple. It might be worth checking with a doctor too. It is strange that the dizziness persisted after eating.

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