Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
7 Jun

Dear Mark: The Low Carb Flu

Conquering carbs offers a whole constellation of rewards, not the least of which is a steady, brisk energy unlike most people have known before (well, maybe since the whirling age of 10 or so…). People tell me constantly that they can finally make it through the day without being down for the count every midafternoon. They enjoy enough vigor and vitality to weather a whole day’s worth of activity. The busyness of life becomes easier to handle: the energy demands of daily work or business travel, the mayhem and constant commotion of kids, a weekend’s worth of chores and errands, etc. A skipped meal doesn’t suddenly change the agenda to including procuring a bagel or other false pick-me-up. Nonetheless, for some folks, there’s a common, temporary but still bothersome bump in the road on the way to that Primal prize. Though it varies, it often means a couple weeks of mental fuzziness, fog and fatigue. Although your body might be off to the races, your brain can lag behind like a little brother in a stuffed snowsuit. It’s a game of “hey, wait up!”  while the body’s mechanisms and metabolism align themselves. They call it “low carb flu,” and rest assured it’s just as temporary.

Dear Mark,

I just want to know if anyone who has been Primal for some time had any trouble with cognition in the first few weeks. I can hardly think straight, especially after eating, and I am also low on energy. Will this pass??? Besides that, my body feels great!”

Thanks to Jessica for her question in response to Matt Garland’s excellent guest post last week. It’s a common subject of emails I receive.

First off, I should mention that some folks experience the low carb flu, and others don’t. Overall, those who have been lower carb for some time seem to have fewer problems with the transition taking their carb intake down a notch. As rational as it sounds, this trend still isn’t a hard and fast rule. I know a number of Primal adherents who fit this profile and then went on to experience the symptoms Jessica describes. Others I know went from sky high sugars to low carb cold turkey and felt great from day one. Go figure. It might be due to the “sliding  range of genetic variations” I’ll be discussing in an upcoming post.

Although the low carb flu isn’t universal, that doesn’t mean it’s abnormal. For many people, it takes about two to three weeks to move beyond the temporary fog and fatigue. Studies following the physical performance of low carbers showed that initial disadvantages were erased after this window of time. 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 expression, increasing 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.

The small amount of specifically targeted research on low carb diets and cognition are small and shoddy at best. A recent study, for example, showed minor memory delay during the first week of strict carbohydrate elimination (as opposed to reduction), but further measures were not taken until carbs were reintroduced. By the same token, those on a traditional American Dietetic Association diet exhibited more confusion during the study tests. I don’t think this study offers any legitimate, useful assessment on either diet.

Nonetheless, there’s the sense that we’re stressing the brain and causing damage by not bathing it in a steady supply of glucose. In fact, we may be doing our brains the ultimate favor. Recent research has pegged Alzheimer’s as a kind of “type 3” diabetes, a disease related to insulin resistance. Truth be told, our brains can function on ketones, fat-metabolism byproducts and key energy sources in low to very low carb diets, which some say may be even healthier yet for our noggins. Check out Jimmy Moore’s interview with Dr. Larry McCleary, a respected neurosurgeon and author of The Brain Trust Program: A Scientifically Based Three-Part Plan to Improve Memory, Elevate Mood, Enhance Attention, Alleviate Migraine and Menopausal Symptoms, and Boost Mental Energy.

Keep in mind also that people in low carb transition can genuinely shortchange their physical needs when they aren’t eating enough fat or when they’re pursuing high intensity exercise routines lasting over an hour, which send the body’s glycogen stores into a nosedive to the ground. I hear this from CrossFitters and P90Xers who insist on maintaining their daily high intensity while transitioning to Primal eating. This isn’t to say that you can’t exercise more intensely for longer on a Primal Blueprint diet (although there’s no real need to for perfectly solid fitness), but more than an hour’s time for most folks requires some extra carbs when glycogen is depleted. If you’re bothered by the mental fog even without intensive exercise, ease up on your carb restriction by adding 25 grams or so to see if it makes a difference. Listen to your body and gauge your sensitivity. Rome wasn’t built in a day, and you’re not going to compromise your overall benefit by taking it slowly.

As any Primal buff would attest, this temporary setback pales in comparison to the benefits once the transition has passed. Without the persistent carb-induced peaks and crashes, you should enjoy a measurable boost in energy – steady and stable – in no time. Hang tight, and know you’ll be on the other side of the hill soon! In the meantime, take good care of yourself with a little extra shuteye and maybe some well-timed green tea for a modest boost when you really need it.

Avid Grokkers: what words of experience do you have for Jessica and other new folks at the Primal table? Be sure to share your thoughts, stories and words of wisdom. Thanks for reading and keep your questions coming!

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. To those of us coming to Primal/Paleo via the Specific Carbohydrate Diet or GAPS, this “low carb flu” is a familiar thing called detoxing, or die-off. Essentially, all the pathogenic bacteria in the gut that feed off extra sugars begin dying off, and this releases toxins into the system. Indeed, even a new secondary round of die-off a few weeks in is known and expected, due to the different types of bacteria. This is a necessary evil for most … it means that your “bacterial household” is resetting.

    JoAnne wrote on June 9th, 2012
  2. I needed this today. Day two of eating primally and feeling a bit foggy. Hopefully it will subside quickly. It is not too bad…yet.

    Mindy1986 wrote on June 16th, 2012
  3. Hey Everyone An observation possibly experiencing no carb flu?

    Full Day #1!
    This morning after my walk with dogs and breakfast of fried onions and eggs I picked up the kindle to finish reading about paleo and got sooo tired… I was sitting up in the chair unable to stay awake. Slept well last night. Lay down and couldn’t get warm
    hooded fleece, 3 animals curled up with me and a blanket, nothing worked. Got up, put on another layer and then started sneezing with a runny nose… (knew nothing about no carb flu at this point) This afternoon I broke a sweat driving in the car and after that the flu symptoms left. It’s 11pm and I’m still feeling full of energy. Holy Jumpins… Normally I’m toast after 8 or 9 pm… Was still out in the woods with the dogs till 9:30!
    no after supper bloating (had a few berries from the garden and woods as dessert)
    Sore tired feet that normally/commonly happened by this time of night haven’t happen – my feet aren’t swollen, my stomach doesn’t feel bloated and my eczema isn’t as bad as it was yesterday… All in my head… who cares!
    Thank you!

    Jennifer wrote on July 3rd, 2012
  4. Ohhhh. Now it makes sense. I didn’t know about the “flu” but I had been experiencing headaches, though I didn’t relate it to the diet. I was so happy with the way things were going that it wasn’t important. I was just surprised because I’d never gotten many headaches. I was one of the people for whom this wasn’t a big stretch, though big enough I guess, to get the “flu”. It’s gone now and the enormous benefits remain. I’ve always felt better on a high protein, low carb diet but was always swayed by the “certainty” of the benefits of brown rice as a staple. Now that I’m grain, legume, and dairy free I’m healthier than at any point in my life. I have energy to burn (at 63) and can go all day. My exercise regimen is now about half what it was with twice the benefits. You just can’t beat this! My weight has stabilized at 127 lb on a 5’4″ frame. I try not to talk about it too much but I always wind up extolling this diet’s virtues when asked why I look so good. I’ve turned the clock back 20 years, effortlessly. If your new, stick with it!

    ellen wrote on July 4th, 2012
  5. Hi Mark, I know this is an extremely late reply to this particular article, but I was talking to a scientist the other day about low-carb diets, and he mentioned that they can cause a brain fog because of low B-Vitamins. B-vitamins are essential for neural function and development, and usually come from grains and the like. Perhaps supplementing them can help prevent or reduce this symptom?

    Sophia wrote on July 4th, 2012
    • Hi Sophia, I’m no doctor, but I can assure you you can all the B vitamins you need from fruits, vegetables, nuts and meat sources. I’ve found that doctors will feed you the old USDA food pyramid crap. I don’t know if they are really that naive, or there is pressure from the big conglomerates who control all the grains to not say anything. If you look at, you will see you get plenty of B vitamins from non-grain or non-dairy sources.

      cindyk wrote on July 8th, 2012
  6. Hey All!
    I have really just dived into my PB lifestyle and am really enjoying eating and tasting foods differently.

    My question is simple: When you all reference “carbs” could you clarify whether you mean Carbs in general, veggies, rice, fruits, grains, or do you mean only good carbs, veggies and fruits?

    I am a novice, so any advice is welcome!

    Tim wrote on July 12th, 2012
  7. I’m feeling a bit crunchy lately. My challenge is canker sores which I’ve had off and on my whole life. Haven’t had them for a while but eating primal seems to have brought them on.

    The primal thing appears to be working though I saw veins on my obliques today for the first time. Hopefully this is what I need to get through the last 5-10 pounds. For those cross-fitters out there I suggest you google Tacfit and plug into that it awesome.

    I think in today’s world full of junk it makes sense to count calories because how can you win if you don’t know the score?

    Aaron wrote on July 19th, 2012
  8. Aha! Day 4 for me. I had to turn back twice this morning on my way to work because of things I had forgotten. Other than the brain fog, I feel great.

    Annie B wrote on August 16th, 2012
  9. since the age of about 14 (now 18) i have experienced a constant heavy headedness/mental fog, aches, and general fatigue – i attribute that all to eating an extremely grain focused diet. after 2 days of the paleo diet, i felt great! now a week later, i definately have the “flu”. I know that if i can just bare with it i will feel better, 2 weeks of flu is better then a lifetime of being ill!

    ashley wrote on August 27th, 2012
  10. Hmm soo jessica has been feeling shitty on the primal diet eh? Could it be the low carb flu? Or is it more likely that she feels so horrible because even though her diet is primal it consists of mostly cooked food

    dylan wrote on August 31st, 2012
  11. I’ve been primal for two weeks now so I thought my experience with this might be worth sharing. I made the switch cold turkey, with the only “cheating” being a serving of yams and a couple of beers over two weeks.. oh and some accidental soybean oil (store-bought mayo..I’m learning). So far, I’ve had nothing even close to the “low-carb flu,” in fact my energy is way up and more importantly it’s consistent. I used to crash every single day at 3pm, but it hasn’t happened since I made the switch. For that fact alone I don’t think I’m ever going back.
    My only somewhat negative experience has been that I get a little sleepy for a few minutes following a higher-fat-than-I’m-used-to evening meal, but I think that’s normal and it fades quickly.. it certainly isn’t severe enough that I would call it a problem.
    As I said I’m a bit new to this, but I suspect that my fellow primal tyros who are having especially severe symptoms may be under-eating.. particularly not eating enough fat. I’ve noticed that it can be hard to overcome the “fat is evil” propaganda in my habits, even though I understand it intellectually. When I’m tempted to eat ultra-lean per my old habits I try to remember this analogy, paraphrased from Mark, “fat is the firewood keeping the house warm, protein is the beams holding the roof up. The beams will burn, but why would you want them to?”

    Josh wrote on August 31st, 2012
  12. I’m having a really hard time getting past the carb flu. Within the first 3 days of giving up bread, rice, soy products, pizza or pasta, I start getting headaches, feel nauseated, anxious, bloated, bowels cramp like hell and I wake up in the middle of the night having dreamed of bread and craving it.

    As I push through to 2 weeks, I feel like a drug addict, always craving, seeking, and then the exhaustion and weariness gets so tough that I start missing days of work as I sleep 12+ hours.

    By the third week I feel like I am a broken human being. I grind my teeth just wanting a hit of bread or pizza. I feel angry all the time.

    After that third week I run out of steam and ability to cope, and go back to the 150g-200g of carbs I was eating every day before I heard of paleo and was losing weight despite it. But now something has become upset, changed, and my body reacts violently and gains 10 lbs in a month.

    So then I try again, fail within two weeks, and another 10lbs flies on. These are not muscle pounds, it’s all fat in the stomach area that has never accumulated like this before. It doesn’t matter how many eggs, meats, veggies I eat, unless I have 100+g of carbs, I constantly feel like nothing ever “satisfies”. I don’t feel hungry, but always feel like pacing as if I’m missing something still, subconsciously chasing it. Carb cravings are cavernous and haunting.

    I’m now 20lbs heavier and scared of Paleo. Before I ever tried paleo, I was losing 20 lbs a year just through gentle portion control. Now my body is so pissed off at my diet change attempts that I’m stuck at a plateau. Whatever I did to lose wait without drastic changes isn’t working like before. It’s been 2 months since my last paleo switch attempt and I haven’t gained nor lost a pound. I’m stuck.

    I’m so envious of friends who switched to paleo and their bodies changed magically, without any physical addiction-like withdrawals. I don’t know what to do except feel a lot of regret. I had a good thing going, a stress free relationship with food that was continuously improving, and then I pushed buttons that upset it all. It will probably take a half year to calm down, get my body to not be so reactionary, and then return to the gradual weight loss I had become so good at.

    Ariella wrote on September 11th, 2012
  13. I’m getting lost in all the comments… so I’ll just re-ask the obvious. Don’t beat me…

    I’m a fitness instructor. I teach 2-4 classes per day (upwards of 15 classes per week). Zumba, Tabata Bootcamps, spin. It is my business, so stopping this level of fitness is not an option for me. This is week 2 of Paleo/Primal and I’m dying. 75-100g carbs is not cutting it for me. Or do I need to wait it out? Help meeeeee…

    B-Sting wrote on October 3rd, 2012
    • yes, increase carbs for lifestyle. bump them up (particularly after a classs). maybe start at 200 carbs a day on hard days and slowly lower it to where you want to be. remember the workouts you’re doing are high heart rate, so you need more carbs.

      Matty wrote on November 8th, 2012
  14. I have gone very low carb this week after 3 weeks of cutting out all sugars, caffeine, alcohol and anything out of a packet with preserves.

    It was tough at the start, but now with the carb drop i feel yuk, headaches, flu like symptoms, & so tired.

    My husband who is a type 1 diabetic told me that I would go into ketosis if I gave up my beloved carbs and this was really dangerous, I know that he sometimes has to check for ketones in his blood.

    I have to pretend im feeling fine otherwise I am sure he would cook me up a pot of potatoes and make me eat them if he knew how ill I was feeling. I’ve really gone off eating and the thought of meat & vege makes me feel sick, today has been the worst.

    I am hoping this will pass and I will come out the other end. I’ve stopped exercising (no energy anyway). All I want to do is do nothing or sleep.

    The other thing I’ve noticed the last few days is my skin colour, I’ve always been a pasty, white, sick looking with dark circles around my eyes, now I have ‘colour’ in my face and don’t need a 44 gallon drum of concealer and makeup….wahooo!

    Jude wrote on October 12th, 2012
  15. As my daughter and her boyfriend have most every imaginable sensitivity I looked into solutions and went Paleo earlier this year. 64 and started at 219#. Couldn’t jog a lick. Fog wasn’t too bad but couldn’t sleep for but a few hours at a time for a couple of weeks that eventually disappeared. Down to 184, did 13 mile run the other nite getting ready for numerous runs and half marathon. Have hit somewhat of a plateau and increasing carbs after long runs seems like a plausible remedy. I no longer experience soreness after heaving indoor cycling and my runs. Now my wife is interested and heading down the Paleo path. Work the plan and the plan will work.

    Bob wrote on October 31st, 2012
  16. Started low carb – high fat diest 4 weeks ago. We went cold turkey.

    I had no such fly but my wife did. Go figure :)

    But it is passed and we feel just great. I just discovered the primal blueprint and this makes perfect sense. We will now complete these new eating habits with the rest of the PB principles. We live near a lake and hilly forest in Denmark, a perfect environment for daily hiking. I will include weight lifting as well. After dall, diet is 80% but I don’t want my muscles to be eaten by my brain either :) (I am near ketogenic at the moment)

    James wrote on November 1st, 2012
    • Jeeze, I type like crap … reaed fly for flu, and diest for diet! Damned …

      James wrote on November 1st, 2012
  17. Glad to read all of this – was starting to feel like I was going crazy. Have been a conscious, but relatively high carb vegan for a long time. Started out introducing some fish and other things, and now settled into a paleo scheme that works for me. But, since I truly stopped the grains, sugar and alcohol – whoa nelly. Tired, able to sleep like crazy (insomnia used to be a problem for me) but a few times have woken in the middle of the night with a SPLITTING headache and feeling really weird. Overall just pretty low key, achy, spacey.

    Hope it passes soon! Thanks for all the encouragement from everybody. It’s very helpful.


    EBG wrote on December 7th, 2012

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