Many people (not everyone!) who start a low carb diet experience what’s called the “keto flu” or the “induction flu” in the first few days while the body is adapting to burning ketones instead of glucose. The basic symptoms are:
- headaches
- nausea
- upset stomach
- Lack of mental clarity (brain fog)
- sleepiness
- fatigue
It’s called the “keto flu” for a reason: you feel sick. I’ve gone through it and it wasn’t a pleasant experience. Fortunately it only lasted 4 days (2 of them were pretty bad) but then suddenly I woke up feeling much better, less hungry and my energy level was really high and consistent throughout the day! While at one point (or three or four) I thought to myself: “what the serious F am I doing? I’m going to die!” but I plowed through it and when it was over I didn’t regret a thing because what I gained mentally and physically was 100% worth it.
How long will the keto flu last?
It depends. Some people don’t experience any symptoms at all, but some suffer anywhere from a day to a week. Rare cases up to two weeks. Everybody’s bodies are different and some people handle switching over better than others. You might consider starting keto on a weekend or sometime when you’re able to get good rest deal with the symptoms.
For those of you that are going through the keto flu, don’t give up! I know you feel like it’s never going to get better but stick with it and you´ll be so happy you did! I’m telling you, waking up refreshed for the first time in years, not getting the afternoon “blah” feeling and stuffing my face with carbs to try to boost my energy is the best side effect of the lchf/keto diet I’ve experienced. Okay, losing weight while eating good food, feeling full and satisfied is great too 
So what can be done to lessen the symptoms?
First you have to understand why your body is reacting this way. Your body’s been burning glucose for energy so it’s basically full of enzymes that are waiting to deal with the carbs you eat (and probably store them as fat) reference. But now the body needs to make new enzymes that burn fat for fuel instead of carbs, and the transition period causes your flu-like symptoms. There are some things you can do to lessen the symptoms of the keto flu and to make it go away sooner (to force the body to transition sooner) Ok, let’s get to the good part – what to do:
- First of all – you’re probably dehydrated. Drink PLENTY of water while you’re on the keto diet. And then some more.
- Watch your electrolytes. When the body is getting rid of excess insulin from your former carb-crazy diet you´ll lose lots of fluids that have been retained in your body. This causes the rapid weight loss most people see in their first few days of ketosis, it’s mostly water, sorry. When you lose all the retained water you also lose electrolytes like sodium, magnesium and potassium. When you’re lacking them you´ll feel like crap so when you’re feeling really ill on the keto flu try things like chicken/beef broth and look for foods rich in these minerals. Take a multi-vitamin and a multi-mineral. I’ve heard good things about
- Eat more fat – Yup, load up. Butter everything, bacon everything, eat fatty meats and put heavy cream in your coffee. This will force your body to hurry up the transition. You´ll think this is crazy and think you´ll never get skinny eating this way, but you will.
- Don’t eat too much protein – The body can transform protein into glucose so if you eat too much of it in the first days it will slow down the transition. Go for fatty meat and cheese if you can, add fat to protein shakes etc. The first instinct when you’re on a diet might be to nibble on a chicken breast to lose weight. Don’t do that unless it’s smothered in cheese, wrapped with bacon and has some mayo on the side
tl;dr: Drink water, replenish electrolytes (sodium, magnesium, potassium) with food and supplements, drink broth, eat fat and not too much protein.
I really hope this helps. I know it helped me getting over the worst of the dreaded keto flu.
Icelandic mother of three little girls - Keto crazy blogger, trying to gather and publish information on the lchf/keto/low carb diet! Like me on Facebook to get update on new posts and more :)
fred May 23, 2012 at 7:55 am
Thanks for your article, i have the flu right now and will try out your suggestions.
Greetings to iceland.
Daniel June 2, 2012 at 11:13 pm
Thanks, this is my second time doing keto. I hear it’s supposed to be easier the second time around, not so far. I’ve felt hypnotised all day today with a horrid headache.
Chris June 14, 2012 at 6:43 am
Also my second time. Never got the flu before. I feel like death. I just keep reminding myself how great I’ll feel once I’m in ketosis!
Lilly June 14, 2012 at 9:21 am
Hang in there Chris, I know it’s rough
You know it´ll be worth it.
Mary July 10, 2012 at 8:07 pm
I began this low-carb “diet”/life style about 3 days ago and I feel like I have a really bad flu. I have not totally eliminated carbs I am just (seriously) limiting the amount I eat… I try to limit fats (cholesterol) as well. I am having a great deal of difficulty focusing and recalling simple things. Will I get over this flu like feeling with limiting carb intake? I was a carb addict!! I did not realize how bad until the past 3 days. Should I keep this up? I have not lost any weight!
Lilly July 10, 2012 at 9:10 pm
Hey Mary
Keep it up! I know it feels awful and like it´ll never go away but trust me, it will. And when it does you´ll feel soooo much better. The way I do low carb is 65% fat, 30% protein and 5% carbs (mostly from green veggies). Are you doing a high protein diet then? In my opinion the fat is essential to feeling full and giving the body enough energy on a low carb diet, too much protein and you´ll put a strain on your kidneys. I was a carb addict too, I didn’t realize but my diet must have been something like 85% carbs before, no wonder we feel like crap while switching over 
Roy December 31, 2012 at 6:44 pm
Lilly – Just wondering, with the 65/30/5 diet, do you limit total calories as well? I mean have you monitored your daily calorie intake – is it low to support any weight loss that you may have seen?
Lilja January 3, 2013 at 1:06 pm
Sorry for the late reply. I don’t limit calories much but I do think about that I eat and make sure I stop when I’m full and only eat when I’m hungry, not our of boredom etc. I have monitored it and sometimes use myfitnesspal.com (with the keto addon – check out caveman keto: http://cavemanketo.com/configuring-mfp/ ) to see if I’m on track. I’m usually pretty spot on with my macros and always amazed at how few calories I’m eating without even trying. I’ve been on calorie restrictive diets before and felt miserable. I’m actually trying right now (you know, new years and all) to log my food on MyfitnessPal and lo and behold, I’ve been adding a few too many calories by putting coconut oil and cream in my coffee all day long. So now I only do that with the first cup of the day
Sneaky calories!
Ann July 13, 2012 at 6:42 pm
Good information! I started 4 days ago and have been pretty heavy on the protein. I’ll cut back on that for the next couple of days. I’ve had a mild headache for 3 days and my concentration is nil. Hopefully all will be back to “normal” by Monday!
Amy August 12, 2012 at 4:30 pm
I am on my sixth day of LCHF and feeling a few things, first a slight bit of anxiety, heart a little racy, hypersensitivity to light and sound, a little euphoria, and nauseated. I’m guessing I must be doing something right to feel this way. Any additional advice you may have and is this normal?
Lauren September 7, 2012 at 5:57 pm
You know, keto flu sounds a lot like morning sickness…
kirsty October 3, 2012 at 8:50 pm
I started the primal diet about two weeks ago and felt great until a couple of days ago. It is such a relief to read that what I am experiencing is normal. I have had a terrible headache, panic attacks and fatigue. I was wondering if it is normal to feel feverish in the night. I have been waking up with the sweats and a high temperature but feeling cold. Has anyone else had this?
Dimitriy October 14, 2012 at 7:47 pm
Help! I’m with a very sick stomach right now. It started on the 6th day of the lchf and it’s second day already. My stool is mostly liquid (almost like water) and I have terrible pains in the stomach. Mind control is actually ok. Just wondering if it can be keto flu or it’s something else I should worry about?
Lilly October 14, 2012 at 8:02 pm
I wish I could help you, Dimitriy. My husband got upset stomach the second time he did keto and eventually it went away. But is truly sucked and I do think it’s related to going into ketosis. You could try asking on a low carb forum or the keto subreddit ( http://www.reddit.com/r/keto ), lots of experienced people talk about keto there and many have gone through the keto flu. At least keep your electrolytes and fluids up and if all fails try asking a doctor.
rad November 20, 2012 at 1:43 pm
Hello,
Ever since I started my Atkins diet,I was looking for some info which was beyond just the atkins website and the book itself.I have been following the atkins for the past 3 weeks and since I have to lose another 50lbs I thought of sticking to induction for little longer.I would greatly appreciate it if you could guide and help me and let me know if I have been doing it right.If it is ok with you,I wish to share my diet and use you expert comments to speed up my weightloss.So far I have just lost about 6 kgs and this is my 3 rd week infact just about to start with 4th.
This is the diet I have been following:
Breakfast
2 egg omelette + 15 ml rapeseed oil + 100 grams lettuce + 1/2 tbsp mayo
Lunch
120 grams chicken(frozen) + 15 ml rapeseed oil + 1 cup broccoli(frozen) + 50 grams lettuce
Evening
2 egg omelette + 15 ml rapeseed oil + 1/4 cup onions + 1/2 cup mushroom + 50 grams lettuce
Dinner
100 grams chicken(frozen) + 15 ml rapeseed oil + 1/4 cup bell pepper + 1/4 cup onions
IN addition to this I drink 1 cup decaf tea using 1 tea bag with 30 ml single cream and add 1 sweetex.
Initially I also used to consume 3 0z of cheddar cheese but stopped it after reading many post saying it stalls weight loss.
Drink around 2-3 ltrs of water every day
Please help
Simone November 29, 2012 at 8:03 pm
Ugh I’m so nauesous, the thought of eating fat is repellant and not appealing! But I will keep eating it. I will prevail!
cookiecate January 4, 2013 at 10:46 am
Thank you for making this so clear and understandable. I wish my Atkins book had helped as much. Thank you.
Margaret Goodwyn January 6, 2013 at 6:51 pm
I have been on the ketogenic diet for four days. I’m usually rubbish at diets and my willpower is not so good but I am managing. The only issue is the keto flu, it is horrid. I have got that warm funny feeling in my throat and nose like the onset of flu. I have also got muscle aches and lethargy. I feel freezing cold but I have clearly got a temperature. I am hoping this will pass soon because I really can’t be doing with these symptoms they make me feel so yuk.
Anyone any ideas if this sounds like keto flu or an unfortunate coincidence?
Many Thanks
Lilja January 6, 2013 at 11:03 pm
Hi Margaret. It does sounds like you might have a touch of real flu, I hope not though. I never had a temperature during my keto flu days. I will say that four days is awesome, well done! The worst is almost over and I sincerely hope you´ll wake up tomorrow feeling better and can start enjoying ketosis and losing weight
Loula January 31, 2013 at 9:16 pm
Thank you for posting this topic! I’m only on day one and after having eggs with turkey bacon for breakfast, I can barely stay awake at work! I usually have oatmeal for breakfast, which I know now is loaded with carbs. What about all the cholesterol in fat, eggs, cheese, etc.? We’ve been taught that’s not good for our heart.
I just read on another website that eating fequently in the beginning stages of the ketogenic diet helps minimize symptoms.
Thanks again,
Loula
Lila February 1, 2013 at 12:18 am
Hi every one! I started the LCHF diet about nine days ago. Will this keto-flu ever go away? On some days it´s not so bad, but some are just terrible. I feel dizzy, very tired, my muscles feel weak, I´m nauseous, stomach feels weird, brain fog (I can´t think clearly) I can´t workout (I do interval training 4 x a week), I feel very hungry every 3 to 4 hours (do I need to eat more fat? (afraid I will gain weight if I eat too much fat. It´s weird for me to eat so much fat) or is that the normal amount of hours without eating? Can´t tell any more since before I would just snack all the time). My carb intake must be less than 50 grs. I just feel sick overall. Is this normal? I keep wondering if I´m making a mistake or I´m not doing it right or maybe this diet is not for me. I´m not over weight, but I do want a less % of body fat and have a healthy lean body (with no junk, no grains). I think my bodyfat percentage is 24% and I want it to go down a bit more. I´m also doing it because I had terrible cravings and there was a point where I was starting to binge (sugar most of the time) and that was when I said “wow, something is not right here”. So yes, now I have no cravings at all, at least I can eat until I´m full and not worry about calories or portions, I just listen to my body and trust it. I do not snack anymore, but I do eat like 5 times a day because I still get very hungry every 3 to 4 hours. Is hunger also a symptom of carb-withdrawl? I´m so happy I can see sweets, and baked goodies and have no desire to have them at all. That is a big deal for me. This a huge reason for me to stick to this diet, but what if I´m always going to feel crapy? Maybe be it´s too soon to tell, but you mention a week or two. So I guess I will wait. I just recently moved to Canada (I am from Mexico) and the food here is soooo diferent. I think I was even starting to gain weight, so this is when I started counting calories, limiting my portions, feeling very deprived all the time and still be hungry with huge cravings It was hell and not working! This did not happen in Mexico. In Mexico I could eat all I wanted until I felt full, satisfied, did not gain any weight at all and almost had no cravings (some sugar cravings since my diet did include the so called “healthy” carbs and some sweets now and then). I was happy
This is why I decided to do some research, found about this diet and decided to give it a try because the rest was not working. My clothes didn´t fit anymore either because I was bloated all the time or I had gained weight. Can´t really tell (I do not have a scale). My clothes still doesn´t fit, but I guess I still have to wait for my body to loose the excess water, start burning fat and get back to normal with this LCHF diet. I also want all the other health benefits that everybody is talking about. Any thoughts, comments, tips or ideas for me?? Thanks a lot!
Josh February 1, 2013 at 5:38 am
OMG, and thank you so much for this article. I’m in the third day of keto and I could of swore I was dying. I was convinced this wasn’t normal. I’ve read that you feel like crap but not like it’s your last day alive. This gives me the strength to keep going.
fatchickfromnola March 10, 2013 at 6:30 pm
Holy smokes! This is only day two and I want to give up. I was sick all last night and didnt get any valuable sleep. I am not hungry at all today… OH and it is only day two. I finally made myself eat something at 130pm and it isnt sitting well with me. I am glad to see your blog and will try and hold on.
BigEvil March 22, 2013 at 12:55 am
Do you go through the keto flu again if you break ketosis even briefly?
Lilja March 22, 2013 at 8:47 am
If it’s only briefly I don’t think you´ll get a full blown keto flu, maybe a headache or feel a little blahh for a couple of days.
Brenda April 25, 2013 at 4:16 am
yes you get the keto flu every single time you break the diet. And for me it is just as bad every single time.
Robert March 28, 2013 at 2:28 am
The type of magnesium can be important. A lot causes diarrhea. Magnesium glycinate seems to work for me.
Patrick April 2, 2013 at 6:46 am
I feel like this right now, minus the headaches. Woke up last night hugging the toilet, because i felt like puking. I’m experiencing nausea, acute upset stomach, and of course fog mind and tiredness.
Vanessa April 5, 2013 at 6:29 am
I have been on ketos for 2 weeks and my flu is the worst its ever been. In addition I had overcome panic attacks years ago and last night I had one for the first time in years. My head is light and I have a raging temp. Dam Dr put me on poisonous meds and I thought this is playing havoc with my Nuro cells. I am not going to give up. My kept sticks encourage me so much. i am on cortisone I hope this wont affect me.
JoyceS April 19, 2013 at 1:12 am
I’m on my 6th day and experiencing Keto Flu. For mr, it reminds me of morning sickness. Always queasy with a very dry mouth. Twice I woke with major sweats during the night. I don’t believe I had a temp either time. I did not get the chills. I feel somewhat less queasy once in a while. I have been trying to load up on fat and water, but forgot about cutting down on protein. I’ll try to do better tomorrow. Regardless of how I’m feeling, I’m not craving anything. My willpower seems strong. I was a very high carb eater prior to this diet. I sure hope I get over this feeling sooner than later.
Lilja April 19, 2013 at 8:27 am
6th day? I’d say you’re unlucky, JoyceS but I admire your willpower. I’m sure it´ll be over very soon and you´ll feel fantastic
Olöf Melkorka April 30, 2013 at 4:58 pm
Hi all, I´ve been on low carb now for abt 3 weeks (slipped 3x). I have been enormously tired. Very irritable. I have some change in my skin color on some parts of my body where skin meets skin. I do not feel really hungry but I get mental cravings.
My dr. does not oppose to this foodplan, neither does my dietist.
I have been a jojo eater for some 30 years, gaining weight rapidly over the years.
I´ll guess I will continue, one day at a time, and hope this flu will go away.
Lola May 1, 2013 at 4:29 pm
OMG – I just stumbled on this info and the timing couldn’t have been better. I’m on day 3 and have all these symptoms. Interesting information about increasing fat intake! It goes against everything I’ve ever known. I’m not giving in though. I’m sticking with it! What do you recommend for protein to fat ratio?
Lilja May 1, 2013 at 4:31 pm
I do 65% fat, 30% protein and 5% carbs. It’s % of calories.