Is Carb Flu Normal?

I started eating better and now I have a headache and am tired-is this normal

I often get this question from people who are new to a healthy way of living and are experiencing some uncomfortable symptoms. Especially if you are switching from a conventional low-fat, high grain diet, you might be noticing that you are tired and have some uncomfortable symptoms like headache, fatigue, achy muscles or brain fog. Don’t worry… you don’t have the flu… at least not the viral one!

This discomfort during the transition phase is often called “carb flu” and should pass in about a week or so. The good news is that you’ll feel much better on the other side and once you start to feel better, all the symptoms go away almost instantly. The bad news is that there isn’t too terribly much you can do make it go faster.

The other bad news (I’m not sounding very positive today, am I?) is that there are things you can do that will make the carb flu worse! Cheating, even a little, at this point will make the fatigue and headache better temporarily, but will make the symptoms worse.

It is completely normal to experience these symptoms as your body switches from burning glucose to being able to use fat and protein instead. As Mark Sisson explains:

If your body is used to employing easy glucose carbs and now must create glucose from fats and protein (a slightly more complex but entirely natural mode of operation), it can take some time to get up to speed. Rest assured that our bodies can and are doing the job. It simply takes time to work efficiently. The transition actually shifts metabolic related gene expressionincreasing fat oxidation pathways and decreasing fat storage pathways. (That’s nothing to shake a stick at!) Within a few weeks, the body should be fairly efficient at converting protein and fat for the liver’s glycogen stores, which provide all the glucose we need for the brain, red blood cells, muscles, etc. under regular circumstances.

If you are interested in understanding more about why the carb flu happens, check out this article at Mark’s Daily Apple  and this very detailed explanation from J. Stanton at

If you’re not interested in feeling like you have the flu any longer than needed, here are some suggestions for cutting down the amount of time you feel this way:

  • Make sure you are actually eating enough, especially of fat. It won’t hurt to eat a few extra tablespoons of coconut oil to make sure you are consuming enough calories and for more energy.
  • Drink enough water! The symptoms of carb flu can also be caused by minor dehydration, so make sure you are drinking enough. You naturally lose water weight during this transition period, so you will need to drink to replenish it.
  • As you lose water, you lose sodium and other minerals as well. Make sure you are getting enough sodium, preferably through sea salt. For me, I felt a lot better when I drank a homemade electrolyte drink.
  • Get enough sleep!
  • Back off the exercise a little, at least for a day or so!
  • Read these articles about staring low-carb from Dr. Michael Eades (whose blog I highly recommend!) Tips for Starting Low Carb Part I and Tips for Starting Low Carb Part II 

How are you feeling? Experience any carb flu or are you making the transition with no ill effects?

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Reader Comments

  1. Rachael says

    So far, so good – I wasn’t as prepared as I’d hoped I would be when this challenge rolled around, but it’s actually been a little easier because we’re on vacation, lots of activity, plenty of food options, etc.  It’s hard to feel bad when fresh seafood and farmers market vegetables are the mainstays.  Coffee – another issue.  I’ve confined it to one cup a day, black and very strong, down from half a pot with lots of splenda, but I don’t see it dropping off the menu for the first couple of weeks.  I can’t tell if I have carb flu or caffeine withdrawal, probably both!

  2. mary says

    This post couldn’t have come at a better time.  I started reading The Paleo diet and haven’t committed completely yet but I have decreased my carb intake dramatically.  I couldn’t figure out why I have been so tired.  I have also had a slight headache for a couple of days.  Your post and the other links you posted made me understand why and not get discouraged.  Thanks!

  3. Kate says

    Great post.  I second Dr. Eades’ articles on starting/restarting low carb.  He says that you will become ketoadapted much faster if you (most importantly) increase your fat intake, don’t overdo it with protein, avoid toxins like caffeine and alcohol, and stay hydrated. 

    Be well,

  4. Amy Gault says

    This explains why the Real Salt shaker has gotten a workout lately.  I’ve been noticing that everyone wants more salt at mealtimes.  I didn’t know that! :)

    As far as how I’m/we’re feeling – pretty good. I was a little tired on my own day 3-5, but now it seems to have passed & I have to make sure I’m wise about how I use all my new-found energy. Boys and I were hungry yesterday, so I think we did need more fat. We all went to bed content after a nice big bowl of healthy yummy whole milk yogurt.

    I love how, even when we’re hungry, we don’t usually get grumpy or tired, just hungry. That’s awesome!

  5. Erin says

    No carb flu here! I feel great – I quit cold turkey and no issues. my biggest problem right now is eating too much because everything is SOOOOO GOOD!
    I can’t win lol  <<< I'm only joking of course, not complaining :)   I love your forum and this outlet – I can't talk about it with my friends without them trying to make it seem like on some crazy crash diet (except, of course, my fellow Crossfitters b/c they eat this way too)
    I notice that when i don't tell people what I'm doing, I can do it better b/c they aren't trying to sabotage me at every corner. My Step dad for instance, when I was doing low fat (i know, I know) would always bring a piece of crappy, fudgy choc cake back from lunch, not for me necessarily, but for my sister who works WITH me. he thought it was hilarious when I had a small bite of it – b;/c he knew he had won out on my goal. Now, i don't say a word – BUT I also don't have those cravings so it doesn't really matter either way. My stomache is not a garbage dump.

  6. Kim says

    Ok I totally have the carb flu, and I did not go cold turkey off carbs I was gluten free first. But I have a headache since yesterday and last night I could hardly pry myself out of bed to feed the baby.

  7. Sherry England says

    Well, I am feeling pretty crappy today and evening. I am doing a yeast detox diet in addition to this wellness challenge and it is biting my butt. I have taken a couple extra Tbsp coconut oil today.I have alot of inflammation throughout, headache, body aches, and literally feel like someone has beat me with a ball bat!!Hoping the coconut oil helps do double duty of giving extra fat and energy and also  combating yeast!!

  8. Angela says

    This post could not have been more appropriate for yesterday.  I was feeling terrible.  Took a few minutes in the middle of the work day to sit by a pond and breathe. That helped a lot!   Head was pounding, something that felt like hot flashes and exhausted. (carb flu)  It made em really excited for feeling great next week once a lot of this “stuff” has gotten out of my body.  Thanks for the great idea of the challenge!  So happy to be a part of it.

  9. Lisa says

    I’ve been a very healthy eater for quite sometime. I workout about 6 times a week including Pilates? Running and weights. I was on a paleo style diet for about 6 months. Recently relaxed quite a bit with my diet and exercise and now I am hitting the healthy trail once again. Every afternoon I am so darn sleepy and I have a terrible headache. I’ve tried a little 20 minute nap only to awake more groggy than when I went down. HeDache worsens as well. By dinner I’ve snapped out of it. What’s going on??? It’s annoying!


  10. Catherine says

    Ive went down this road a time or two in my weight loss/ healthy living journey. The first week or two is always treacherous! I always told myself it was my body ridding itself of impurities; which is true, but apparently more complex. The headaches usually start as early as my first day; a trigger being as simple as consuming more water. Then I get nauseous, followed by the fatigue. It is always so disappointing when you’re trying to make a healthy change and feel like garbage. The cherry on top would be the nausea and queeziness finally surfacing itself half way through the week. I need not go into detail on how. I’ve hit that point today. My head is swimming and so is my stomach and I dislike taking medicine :( However, I have enjoyed my journey so much and all the interesting research that I have decided to go back to school this year to be a Dietitian (RD ) Ive never heard of Carb-flu. I’m so grateful to have come across this article. It definitely gives me some hope in my current situation! Thank you ! And GOOD LUCK EVERYONE !

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