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. You have to believe. It’s as simple as that.

    Write down EVERYTHING you eat and go by the numbers. The Daily Plate on is an EXCELLENT resource to track your eating habits. Pick a healthy protein/fat/carb ratio (1/3’s is not a bad place to start) and stick to it. It WILL get better. And once you’re better, there’s no way you’ll ever want to go back to the “old way.” You’re going through “carb-junkie detox,” and you just need to grind your way through it.

    If you’re an athlete, you’ll obviously need some extra carbs either during or post workout.

    After 90 minutes, your muscles will be out of glycogen, so if you’re going over 90, you’ll need to start taking in some sugar prior to that. Everyone’s different, so let your body be your guide and don’t go crazy. You don’t need to pound down a half-dozen cliff shots prior to a ride like I see people doing all the time. There’s a lot of healthy and creative solutions. I stick a honey bear in the bento bag on my bike for longer rides. Just based on experience, I know what timing of sugar intake is enough that I recover easily and don’t feel like dookey post-workout. Cheap, simple, natural, and best of all – it works great.

    If you were eating hard-core paleo and did a long, hard workout with no carb intake, that could be the reason for your suffering. It took me a solid week to recover from one of those mistakes. But you will recover if you let yourself and life will get better.

    Eric wrote on June 7th, 2010
    • “Pick a healthy protein/fat/carb ratio (1/3’s is not a bad place to start) and stick to it.”

      Umm…what? I think you want the Atkins forum over there—-> :)

      JohnC wrote on June 7th, 2010
      • Hey, I’m not shilling for anyone. I went to nurse/dietitian that specialized in setting up nutrition plans for triathletes. I didn’t list *my* ratio because my ratio was custom tailored for me based on actual metabolic measurements. I wouldn’t know an Atkins plan from a hole in the ground.

        My only point is that if people ate in 1/3’s, that would be at least *half* the normal number of carbs and double the protein the typical person is eating in a day. I know Mark advocates less carbs than that, but for many people, looking at a pie chart on Daily Plate and just making it into three equal “slices” if you will, would be a dramatic step in the right direction.

        Start there, then let body awareness guide you the rest of the way.

        Eric wrote on June 7th, 2010
        • I didn’t think you were shilling, I was just surprised that you were posting on a site about primal nutrition, among other things, two things that go so entirely against the essential nature of primal eating: weighing measuring and recording and eating such a huge percentage of carbs.

          JohnC wrote on June 7th, 2010
        • I think if you are trying to lose weight you may have to count calories (I know I need to because even eating primally I can accidentally eat too much because I’m eating calorie dense foods). But 1/3 carbs is definitely too high for me (I eat an almost ketogenic diet).

          Sarah wrote on June 7th, 2010
        • Thirds isn’t primal – my breakdown is 20% protein, 15% carb, at least 60% fat (by calories) balance is a glass of wine – that gives me just under 100 g carb tops per day and I’m an athlete.

          I had massive detox for 36 hours – shakes, mental confusion, night sweats, the lot – real cold turkey stuff – that was cutting all grains and added sugar from my diet – I was high carb low fat CW athlete nutrition. After that I felt like a new person.

          Believing and having faith is the key and as my brother said tonight when he phoned (75 lbs lighter this year)Primal Law 0 have a Grok buddy to support you, failing that keep reading MDA!


          Kelda wrote on June 7th, 2010
        • Did you have to mention pie? I just started the switch to Primal eating two days ago. I don’t feel like I have carb flu, but I wasn’t a huge grain eater really. My weakness is desserts and treats. Luckily for me though my cravings are most intense just before menstruation begins and I chose to begin eating primal just after my cycle ended (over share?). Hopefully by the time the intense cravings come around, I won’t have them this time. Only time will tell but so far it’s been easy, I’m sure I’ll get hit in the face by those cravings in the future, but I’m trying to think positive and hope I can breeze through those hurdles and continue on down the path. I’m quite pleased I’ve made it the past two days, particularly with the chocolate chipp cookies sitting in my cupboard as we speak. Wish me luck and LOTS of will power!

          Venna wrote on June 10th, 2010
    • Not sure how to respond to John C directly but a lot of people use the Biggly software specifically for tracking their progress with primal eating and workouts. Measuring and using progress as motivation is hardly breaking rules or something..?

      Alan wrote on August 31st, 2012
  2. I guess I was lucky then. I didn’t experience the low carb flu.

    Organic Gabe wrote on June 7th, 2010
  3. “but more than an hour’s time for most folks requires some extra carbs when glycogen is depleted”. Of course everyone is different but my experience over the last 6 months of gradually building my capacity is that I can routinely do a 2500-3000 yard masters swim set on a saturday morning and then go ride 30-50 miles with time trial effort, hill sprints or hill repeats depending on the workout, all on water and salt tabs – and Trust me – I am no genetic marvel – very much a 47 year old middle of the pack age grouper. It just take a little time.

    John M wrote on June 7th, 2010
    • I just did a 34 mile bike ride without carbs. eggs for breakfast, then just coconut water with coconut oil added for some fat.
      Then there were the others. Some younger riders were participating, I guess for the first time, and the parents were encouraging bananas and cookies “because you need lots of carbs for energy when riding”.
      I wonder if that’s why some many riders I see have pot bellies?

      Dave, RN wrote on June 7th, 2010
      • Check the carbs on coconut water. You took in at least as many as those eating bananas.

        How can some people here be so blind to the nutritional makeup of their food in order to maintain claims of “being low carb”?

        Fred wrote on June 7th, 2010
        • And you seem a little confused about being low carb vs primal vs a lower carb athlete

          wd wrote on June 7th, 2010
      • You’re an RN, Dave? And you seriously believe people get potbellies from eating too many bananas?

        Produce even one such person and you’ll likely make medical history.

        Get real.

        Fred wrote on June 7th, 2010
        • I didn’t say coconut water had no carbs. My point was that loading up on excessive carbs over a period of time can result in mesentery fat accumulation. I know this from experience. I had a 30 lb gut on me from my high carb diet. I was real good at hiding it too. I had backaches from sucking my gut in all the time.
          As for the coconut water, I used that instead of the typical “sports drinks” because It contains similar levels of electrolytes as those found in human blood, and in fact was used in place of plasma in the Pacific theater in WWll when supplies of plasma were low. That and it’s not an artificial. Yes it has carbs, 14 in the container I drank. One banana has 23 grams, and I’d eat 2-3 on a 30 mile ride in the past, along with cookies and oranges. I also didn’t say how much I had. So let me be more specific; 11.2 oz (14 grams), with 5oz of oil, (0 grams). The rest was water.
          So, 14G carbs vs. a typical ride for me with 75-100. That was my point.
          And then I went and did two hours of martial arts. Then I came home and had dinner. My point there being it wasn’t necessary for me to go home and load up on carbs and “recover”.

          Dave, RN wrote on June 7th, 2010
        • Interesting debate!

          I just rode a Sportive – 81 miles, and I rode hard, 6,000 ft climbing and clocked 4:24 (average heart rate 80-85% of max) – around 10 g of carb from raw fruit/nut bars an hour with water and electrolyte salts … the longer you train low carb the more efficient your body becomes. And breakfast was eggs and bacon with some full fat Greek yog and berries with a teaspoon of clear honey :-) … carb loading – who needs it!

          Watch this space for Primal endurance activity in action, I start on 12 June …

          May be I am a genetic marvel – but I doubt it – I’m certainly super efficient at fat burning for fuel though.

          Kelda wrote on June 7th, 2010
        • It is a fact..bananas do cause pot bellies. Have you ever seen an ape withut a pot belly?

          jo wrote on April 26th, 2012
        • Massive supply of fructose, are you kidding? Goes straight to the liver and turns into fat. Be one of these people who eats pounds and pounds of fruit daily (only they make it into smoothies) without also getting enough choline to counteract it and you’ll wind up with a lovely case of non-alcoholic fatty liver disease.

          It doesn’t always mean a pot belly but if you could get the pot belly without the NAFLD, believe me, you’d rather have the pot belly.

          Dana wrote on July 18th, 2013
  4. Interesting. If I recall, I went primal on a Monday or a Tuesday and I began having flu-like symptoms before that first weekend.

    After 4-5 months of success, my wife tried to go primal and she too had flu-like symptoms her first weekend. Glad that it passes relatively quickly.

    CJ wrote on June 7th, 2010
    • Any idea how long the flu-like symptoms can last? My husband didn’t get them, but now I have been going primal for a month and still have flu-like symptoms. I keep hoping this gets better because I really want to go primal, but honestly it’s making it hard. The last 2 weeks have been a nightmare… My guess is that my diet was so high in carbs and sugars my body is just freaking out, but i feel like i can’t take much more.

      sharice wrote on August 25th, 2011
      • The flu-like symptoms are the die off of the bad bacteria (including candida) in your intestines. They aren’t getting all the sugar and gluten to eat, so they are dying and releasing all their toxins all at once. I guess if you had a lot, it could affect you for a while. My niece has over 17 food allergies including gluten, dairy, and corn. She went through the mill with the die-off symptoms.

        cindyk wrote on July 8th, 2012
      • I’m on week three and I feel about as good as a dropping from a grass-fed cow. My body might be healthier, but I still feel like s***. If I don’t get any relief soon I might resort to adding more carbs in the form of sweet potatoes and maybe some whole-fat dairy w/ fruit. (I’ve been eating sweet potatoes and fruit, just trying not to go overboard on them.) I don’t want to give in, but I’ve honestly felt like I’m not safe to be driving at times. This blows. I want to feel all the wonderful things that others have reported!

        Alika wrote on May 15th, 2013
        • If you intake enough oils in your daily routine, you won’t feel like that at all. Try to make a 3 egg omelette in the morning with olive oil. Then have a large salad with olive oil and balsamic vinegar in the afternoon. For me personally, I think it is the fat that makes me feel satisfied.

          James wrote on May 21st, 2013
        • me too! that’s why i started asking around about low-carb fatigue. i’m like a zombie, and have been for over 3 weeks now… and i’m also dangerously close to stoking the carb-o-retta…

          did you notice any progress/positive change yet?

          adam wrote on June 18th, 2013
        • Good news folks–I’m feeling much better now! Hopefully this means you will too! I think it just takes some people more time than others. You can experiment with your fat/protein/carb ratios all you want, but in the beginning, I think you just have to do whatever works (if that means a few more potatoes or fruits or rice, so be it). Now that I’m on week 8, I don’t feel the need to eat too many carbs. I’ve also added in some dairy in the form of goat yogurt and grass-fed cheddar. I love being able to go for long stretches without eating and not feel like I’m about to pass out with hunger (previously I was consuming about six small meals a day and if I skipped one I’d get cranky real fast). I’m still adjusting and seeing what works best for my body, but overall I feel better and trimmer (even though the numbers on the scale haven’t dropped drastically, my clothes feel looser and I think I look better, so isn’t that all that matters? 😉 ). Before the Primal Blueprint entered my life, I was a carb queen and could inhale a bowl of pasta no problem. Now I look at it and think of how crappy I would feel afterwards. Keep trying you guys! Once you start feeling better, then you can access to see if this all has been worth it.

          Alika wrote on June 18th, 2013
        • I don’t know about intaking “oils” but fat generally, yes. Eat some animal fat if you’re not already. Olive oil’s nice but not as the only fat you intake.

          Dana wrote on July 18th, 2013
      • Yes, when does it end. It is 3 weeks tomorrow for me (cut out all processed foods but I had only been eating after lunch chocolate 500 calories) and fruit. I still feel as if I have a germ, sore eyes, tired all the time (yet in bed mostly asleep for 8 – 9 hours a night), nose slightly blocked as if I have a mild germ about to come out.

        You would have thought by nearly going into week 4 it would be over by now. Also only lost a pound in weight at best. I am however sticking with my 3 meals a day with a brown carb, eg baked potato, brown basmati rice or sweet potato with skin. I suspect giving up those “brown carbs” is not going to make me any happier, just worse so do not want to be rid of them or I could derail the whole process. My cravings for sugar have gone but the feeling that someone is sitting there draining energy from me all day is absolutely horrible and I wish I knew if I had some other kind of germ or if it is due to giving up fruit. I do not want to reintroduce fruit or dried fruit as I have always been addicted to it and it is a kind of triumph I have managed 3 weeks without any.

        EnglishRose2012 wrote on June 13th, 2013
        • No, you probably better drop the brown carbs. Kind of missing the point there.

          I can tell when I’m eating too much starch because I wake up groggy. If you are just hanging “in between” SAD and Primal you are going to cause more problems than you solve. Besides, that stuff’s almost empty calories. Take up the calories with something more nutritious.

          Dana wrote on July 18th, 2013
        • I disagree w Dana about “causing more problems than you solve” as well as her statement that potatoes (both white and sweet) being empty calories. All potatoes, white, red, sweet and yams, all high carbohydrates and (a blasphemous) starch, nevertheless have a lot of nutrition.

          However, I do agree w Dana on the fact, to become fat-adapted and in a ketogenic state, a person needs to follow a VERY low-carbohydrate diet. Otherwise one will never fully fat-adapt. Unfortunatley, for some people, the process of adaptation, can be a brutal hell to attain. I’ve heard it said that it can take as long as 6 weeks. (I was practically immobilized w fatigue for close to 3 weeks when I decided to cave-in and eat a spud) The problem, at least for me was: who has the kind of time to hang out feeling miserable, unable to function until our body heals and decides to adapt? Most of us have all sorts of commitments, families, work etc.

          Hence, my potato defense…

          According to Cate Shanahan MD, a major player in the low-carb/ketogenic community of doctors states: that adding healthy carbs, like sweet potatoes and even (demonized) white potatoes to our current low-carb diet in extreme moderation and on a temporary basis (key words: moderation and temporary) is a healthier approach than going “cold turkey”. After all, initially we should be starting at “low” carb not “no” carb. Shanahan says: for those who struggle w adaptation, fatigue is your body’s way of fighting back. Adding small amounts (according to each individual) of slow-burning carbohydrate to our diet can be part of the process that eventually will take us, if we choose to do so, to a VLC ketogenic diet and lifestyle. A gradual type of titration if you will…

          Dr.Shanahan maintains that it doesn’t make sense to go from a highly processed high-carb standard Am. diet (SAD) to an extremely low-carb Ketogenic diet and expect our bodies to feel good about it. Those that do adapt immediately or within a few short days are the exception.

          We don’t lose weight to get healthy. We actually get healthy first, then we will lose weight. We do this through the 4 pillars.
          (1)Diet (2)Sleep (3)Stress reduction and (4) Appropriate exercise.

          It has been my experience that working my way toward a specific dietary health goal, by using dietary tweaks along the way, is more beneficial and rewarding than jumping in w both feet and feeling miserable. As many have already expressed, adaptation is a strange phenomena… some folks adapt within a day or two and (at least appear to) live happily ever after. The rest of us are blasted by fatigue, brain fog, muscle cramping, adrenal/thyroid issues as well as hair loss instead of weight loss.

          Lastly, I think more research is in order.

          GoodStew wrote on March 20th, 2016
  5. Agreed with Eric. I experience the same thing. I was wondering why I was still hungry and tired all the time when everyone spoke of energy spikes and feeling more fulfilled after meals.

    I gave it 2 weeks pretty strict, and soon, I was off to the races! The main thing I have noticed is my recovery time after a touch workout (I’m an avid CrossFitter) has decreased dramatically, and I’m not NEARLY as sore the next day.

    Another thing I’ve noticed is a different kind of body awareness. I’m now so much more aware of when I’ve had too much sugar, even in the form of fruit, or too much meat. Now, when I eat even a little bit of bread I feel hung over the next day.

    It’s incredible the changes you’ll feel, and most certainly see. I, personally, did not have any weight to lose when I started eating more Paleo, but I have gotten smaller (I lost a pant size) and gotten much leaner in only 2-2.5 mo’s. I do “cheat” sometimes, but those moments only serve as a reminder of why I eat this way. The next day or even within a few hours I can feel the grossness coming on.

    My main point? Keep with it! Write down EVERYTHING you ingest (including drinks, gum, snacks, even if it’s just one peanut…they add up). After a week, take a look back and see how you did and how the balance is. Remember that a balanced Paleo diet is key, not just eating foods that are Paleo. Too much fruit can give you a sugar high, and too much meat can make you feel sluggish (it does for me, anyway). Learn to listen to your body, and your brain will catch up.

    Best of luck!

    Emily wrote on June 7th, 2010
  6. To me one of the big benefits of eating Paleo aside from health is *not* writing stuff down, *not* weighing and measuring.

    If I wanted all that stress and hassle in my life I’d go on a diet or something. 😉

    JohnC wrote on June 7th, 2010
    • I agree, but when I feel myself falling off the bandwagon, I start writing everything down to help myself get back on track. That’s also how I started and it helped me stay away from all the nasty stuff out there. Writing things down helps me check the balance in my diet, too.

      Emily wrote on June 8th, 2010
  7. Great post! I too experienced some issues when I went Paleo. I was mostly just sluggish, more tired than normal during the day. Felt like taking a nap, which I never used to feel. It got better though, mostly after about a week or two. As the post suggests, just stick with it and those ‘carb withdrawls’ will eventually pass.

    Ray wrote on June 7th, 2010
  8. I remember getting “carb flu” after doing GOMAD (gallon of whole milk a day) about a year ago for around a month ( went w/ my strength training at the time) – After which I switched to only having starchy carbs post work out only. I didn’t know what was wrong with me, I was totally shattered for the first week. Over time my body adapted better & better as my diet became more primal over the next 6months or so.

    Matt wrote on June 7th, 2010
    • Why would you want to breast-feed if you were doing strength training?

      JohnAtl wrote on June 7th, 2010
      • That, sir, is a stupid response and no better than troll-bait.

        Alchemyguy, Science Bulldog wrote on June 7th, 2010
  9. No carb flu experience here :)

    I think newbies need to just take baby steps. There is no need to rush things. You have probably been eating the way you were eating for several years… so why try to all of a sudden cut your carb intake in half or more overnight? Ease into it… cut 50 carbs for the first week then 50 more… or even do it in 20s.

    I just try to advice baby steps in everything in life… we are all so rushy rush! Life is NOT short. We shall all be grateful that we are all living!

    Good luck all newbies – you will get to the magical feeling soon when you will NEVER look back to your ole ways! Living primal is like living in an entire new world :) :)

    Primal Toad wrote on June 7th, 2010
    • Some of us like to just rip the Band-Aid off and get going. It may be too much for some and cause them to give up but for others it’s best to get it out of the way while the motivation is still high.

      I know when I first tried Atkins years ago I only made it 3 days the first time and gave up. The next try, I cut out sweet tea and fries for a month first then tried induction and I made it through. Too bad I didn’t find Paleo back then cause all the fake bars, shakes, maltitol/sorbitol chocolate bars, and absolute “low-carb” crap combined with too much protein and too little fat (and the wrong types) caused me fail. I started Atkins style 5 months ago and found Paleo 1 month in and have been going strong ever since.

      Jonathan wrote on June 7th, 2010
      • You don’t have to use the shakes and carbs to do Atkins. I’m kind of peeved that I keep having to tell people this. I know this is an old comment I’m responding to, but I feel compelled to correct misconceptions.

        The bars and shakes were created to supposedly make the diet easier for some people (and, yes, to make money for the company). But you can do Atkins without once touching them. You can also do Atkins with just Primal or Paleo foods. While Atkins does have a list of foods you are allowed to eat in various phases, it does not mean you are *required* to eat all those foods. For example, up to the last book Dr. Atkins published while he was still alive, soybean oil was allowed. But I could avoid soybean oil and still be Atkins-legal.

        Atkins is useful as a tool to break addictions and find one’s personal carb tolerance. In that light, for some people, it is invaluable. Let’s stop pretending otherwise; I’d be willing to bet everyone slamming it never bothered reading the book anyway. FWIW, one of Dr. Atkins’s motivations for encouraging people to try low-carb was that it was more like the way “cavemen” used to eat! Sad that he was probably more tolerant of the idea of Paleo than Paleo people are toward his diet today.

        Dana wrote on July 18th, 2013
    • Do you ever have problems sleeping on low carbs? I feel much better since I switched to eating fat/protein foods for breakfast and lunch, but if I eat a meal of meat and veggies alone for dinner I just won’t fall asleep, so I usually toss in a few pieces of fruit for desert to help induce the sleep. I did a little research and found ketosis tends to increase the time in deep sleep in exchange for REM sleep. I was just curious if you had any experiences with this, or what your thoughts were?

      James wrote on May 15th, 2011
  10. I’m one of those that went from high carb (whole grain breads and soy spreads) to the PB cold turkey and felt great since day 1.

    BUT, after 3 weeks exactly I had a HUGE sugar craving…what I didn’t know at the time was what Mark states in his article: Don’t go low carb + work out more than necessary, which I did every day for 3 weeks straight.

    I gave into the sugar craving because I did not know how to fight it…i binged on mexican pastries for 2 days straight.
    Not smart but it worked at the time. I have been 100% primal ever since for little over 2 months now without a single craving.
    Those 2 binge days made me feel so crappy that it’s not worth repeating if it ever happens again.

    Now I have pure grass-fed/finished kidney fat to fill that hole. Works like a charm:)

    Suvetar wrote on June 7th, 2010
  11. You’ve got to make sure you eat enough fat.

    A lot of us have been brainwashed into being afraid of eating fat. I got over my low-carb flu after cooking up all the bacon in the house and eating as much of it as I could. Felt awesome immediately after that.

    Now, whenever I feel run-down I have some pastured eggs or raw milk and it picks me right up.

    Tuck wrote on June 7th, 2010
  12. I struggled with cravings but not with any mental stuff. My skin got oily and I broke out as my body transitioned to a high fat diet, but thankfully that only lasted about three weeks to a month as my body cleansed itself. I read a while back that some new comers were struggling with the same thing.

    mike wrote on June 7th, 2010
  13. Thanks for this post Mark. I definitely got the “flu” after going Primal. I have had a few bouts of anxiety in the past and these symptoms seemed to exacerbate the problem. As a cyclist and runner, my body was used to a high-carb diet and rebelled when I cut them out. I actually felt so bad that I reintroduced some brown rice, some potatoes and sweet potatoes. Now I realize that I was doing too much too soon. For me anyway. I’m 6’3″ and 199 lbs. so I need to make sure I am getting enough calories and especially fat while reducing carbs. Time to begin again. This time a more gradual approach is in order I think.

    Brad Gantt wrote on June 7th, 2010
  14. I’ve been 90% primal for about 3 months. My 13 yr. old daughter just started last week. Neither one of us has had any negative withdrawl-type symtoms, though we both had different eating habits before going primal.

    I can’t say for sure why this is, but we both eat a primal diet of about 60-65% fat, and shoot for .8 grams of protien per lb. of lean body mass, and a carb intake of 50-65 grams (per day). We don’t focus on calories, but they usually work out to be around 500 per day less than needed to maintain weight.

    We use FitDay to keep track of everything we eat for the first couple of weeks. It helps in the transition phase to see how the actual numbers add up. I didn’t find it necessary to keep track after that.

    My daughter wanted to go primal after seeing what I had accomplished in 3 short months. I was about 45-50lbs. overweight. I’m down 20lbs and feel terrific compared to before. We both are looking to be close to our fitness goal by the end of September. At that point we should both have reached “before & after” status!!

    For those of you just starting, get excited. This works. This is right. This is the real deal. Just follow the Blueprint on this blog. All of it.

    A word about exercise. Don’t worry about motivation at first. You will definitely want to exercise more and more after you begin eating right and the pounds start coming off and energy levels rise. You won’t need anyone to tell you to do it, or make you do it. You’ll want to do it.

    NotSoFast wrote on June 7th, 2010
  15. I never got the “low carb flu”, but it sounds like what Masters Ultra Runner Rob Evans had happen to him. He is interviewed by Scott Dunlap over at his very popular “A Trail Runner’s Blog”
    and talks about 3 tough weeks after going high fat,high protein,low carb, but how this diet has been a big part of his newfound success.
    Lots of ultra runners and endurance athletes going primal these days, with great results.

    Digger wrote on June 7th, 2010
  16. I started exactly one week ago–the first few days were ROUGH. I had zero energy, making my CrossFit workouts nearly impossible. I read a bit about easing into it, and had a sandwich here, some pasta there…I was maxing out at 1,000 – 1,100 calories per day…not good. Now things are better, but I don’t feel any better than I did before I started Primal eating. If nothing else though, following this site has eliminated chips and beer (almost) from my diet. Keep up the excellent work Mark.

    Matt wrote on June 7th, 2010
  17. Mine lasted for 6 foggy weeks. Everytime I would get close to breaking through, I would give in to the sugar craving and was too scared to eat THAT MUCH FAT lol. Hindsight, as usual, is 20/20 and I should have just brought on the bacon/avacado/coconut oil/steak until I felt better.

    In other news, if you fall off for a while then return to HF-LC, the “flu” lasts considerably less time… I’m guessing because you’ve already adapted once before, so it’s not a “new” thing to your body.

    Cliff wrote on June 7th, 2010
  18. Sometimes the low-carb flu is a result of a lack of veggies. In my previous low carb experiments I ate only meat and cheese, very acidic of course. That is what got me sick until I brought up the veggies again.

    Someone mentioned above that they experience hang-over symptoms from white bread and processed flour products. I get that too now!

    nathan wrote on June 7th, 2010
    • All protein, even plant protein, creates acid in your body, but your kidneys are adapted to buffer that acid. If you eat animal protein, it even comes with its own buffer: the amino acid glutamine. You are not ever going to make yourself “acidic” enough to get sick unless something is wrong with your kidneys. You might have been reacting to the casein in the cheese, though. Lots of times when people want to transition to Paleo or Primal due to gluten sensitivities, they have wound up with casein sensitivities as well. And there is a lot of casein in cheese.

      Veggies have some utility for both micronutrients and hormetic effects (look it up), but a human being can go entirely meat-only and do just fine. In fact we would have had to do so during glacial periods if we lived far enough north, and of course the Inuit did that for large portions of the year before whites encroached on their territory.

      Dana wrote on July 18th, 2013
      • I like you. Everywhere I go the veggies follow me…::sigh:: first you defend dr atkins, who saved my life ten years ago when was first dxed as a type 1.5 diabetic, then you defend my food choices hehe. Definitely like you. Hi, Im Marie :)

        Marie wrote on February 4th, 2014
  19. I seem to think the low-carb flu is related to carb addiction. Wheat and other grains contain opiates and when people break this addiction, as with any junkie they go cold turkey for a while.

    Craig wrote on June 7th, 2010
    • I totally agree with this. I think the severity of mine is because I was unaware of how much my mood was relegated by sugar before. It was sneaky because it was mostly fruit and chocolate and alcohol, not grains. But all the advice is extremely helpful. More fat is a hrad thing to wrap your head around if you previously listened to CW…but it definitely makes a difference for me. But it’s something I have to remember and then force myself to eat! Good luck everyone.

      Christina wrote on June 7th, 2010
  20. Never got the carb flu. I did get depressed once just thinking about no carbs….lol. I love the no or little carb lifestyle. To make it easier on your self, plan some cheat days here and there, this will give you something to look forward to on your journey. Remember to set your goals, long and short term and take it one day at a time. My mother gets brain fog just at the thought of no carbs….lol

    Rob wrote on June 7th, 2010
  21. I had about 3 days of low-carb flu, I haven’t measured *anything* (calories or ratios) and I’ve been losing weight really quickly.

    quette wrote on June 7th, 2010
  22. I’ve been doing Paleo for athletes for about 1 week. I was really tired after about 5 days but today I’m feeling good. My problem is that I’m still getting cravings, but I just eat berries to try and subsided them.

    Robert Gioia wrote on June 7th, 2010
    • Those cravings go completely away at 20 grams of carbs a day or less. You might try different levels of carbs and see what works for you.

      Rob wrote on June 7th, 2010
      • I went low carb (not paleo) 8 years ago and settled into about 60-80 carbs a day. The carb cravings completely left.

        I went back to a more CW diet (grains are everywhere, it became hard to fight). I stopped losing weight and this little pot belly just won’t leave.

        I’ve started stumbling towards a paleo diet this time; the whole approach just seems so sane, and I could use a little more sanity in my life. I’m back to having those cravings but know they’ll leave when I hit <100 gms carbs for a week.

        p.s. I don't think I ate enough fat last time…got to find some good bacon (everything in this town is full of "…ites" and "…ates")

        Chris Johnson wrote on September 19th, 2011
  23. into week 3 as of yesterday, and just now coming out of the fog and grog of carb flu. My diet was heavy grains and legumes just prior to Primal, so I imagine that I am in for a bit of a longer battle shaking it all. Feel good though, and some days are better than others. My workouts definitely suffered, but I am finding my new sweet spot in regards to my Kettlebells and lifting. I am having a tougher mental battle over the bacon thing right now…
    all in time I suppose!

    Sandy wrote on June 7th, 2010
  24. The closest I’ve come to the low-carb flu was a few splitting headaches when I tried reducing my carb intake to near zero. Eating ad libitum paleo was keeping me a bit paunchier than I’d like, and it took calorie counting on for a couple months to lose the extra 13 pounds. During that time, my daily carb intake ranged from about 80-120 grams, which was enough to prevent ketosis and headaches, but not so much that it created that voracious gnawing hunger that larger amounts of carbs do. On days when I was less physically active I could eat as few as 1500 calories and feel only the gentlest of hunger impulses.

    Alex wrote on June 7th, 2010
  25. I’ve been “easing into” primal over a few weeks now and have not experienced anything flulike; However I had a carb overload this weekend and felt like utter crap. Go figure.

    Ely wrote on June 7th, 2010
  26. It hit me at the start of my second week and lingered for a week, but only two days were like being out sick with the flu. The rest was just a little weak and foggy.

    What made this easy for me though was I started with high blood pressure and high blood sugar and both numbers were falling into nice normal ranges during that second week.

    It also helped to have a wealth of information available describing what I was experiencing. So thanks for adding to that, Mark. If I ever win the converts I’m working, I’ll point to this post BEFORE they get hit.

    Grol wrote on June 7th, 2010
  27. i realize we are in a sense, detoxing from conventional wisdom but more literally, from carb overload.

    is there a connection/similarity between going primal and detoxing?

    while i haven’t gone through these flu like symptoms while going primal, i have experienced it going through fasts and cleanses.

    Hyun wrote on June 7th, 2010
  28. I feel your pain girl!!!!! My goal was to do no carbs, no sugar, no fruit and no caffeine for a month. I lasted about 3 weeks until I had some birthday cake. Now I’m back to feeling that icky feeling, however, it’s not as bad as it was the first time. I binged for about a week on that dredded cake. However, I know now that your energy does pick up and what kept you going before (carbs, sugar, caffeine) is no longer needed. Water replaces the caffeine and I ALWAYS will have some protein and veggies with me at all times; because good decisions never happen if you’re not ready with your food. Unless you’re that diciplined. :) I could feel my motabolism pick up when I’d get hot every so often. It definitely will be worth it once you get there. I’m on my way again. This time with more self control! :)

    Christina wrote on June 7th, 2010
  29. I definitely felt the pangs of the Primal flu…my body was achy, my head hurt and I was exhausted but could never fall asleep.

    It lasted about 1.5 weeks and then BAM I felt awesome! I now spring out of bed and feel full of energy all day.

    I’m slowly converting my friends to Primal, but I always warn them of the flu they’ll feel at first. It’s worth it to stick it out though!

    Liz wrote on June 7th, 2010
    • I am having this issue right now but it’s so bad, I wake up with huge headaches in the morning, I am super exhausted but can’t fall asleep, really light headed if i stand up too quick, I feel lethargic and down. I ate some white bread today because i thought it would help. It didn’t. I don’t have any cravings though which is a bonus I guess.

      L wrote on June 5th, 2012
      • @L – Your symptoms sound similar to mine – total exhaustion, unable to sleep, feeling weak, dizziness when standing…I’m now on day 13, and it is the first day since starting that I feel half-way decent. It hasn’t been all bad though; my skin is clearer and I’ve lost 7 lbs.

        Jackie J. wrote on June 9th, 2012
      • I have these kind of issues, an last time, end of the day and feeling really dizzy, I cheated with a big smoked meat sandwich. Feeled totally okay after. I tought that time that it was the bread from the sandwich that get me better just after the meal, but not i’m beginning to think that maybe it was the big amound of protein+fat

        Jan wrote on July 8th, 2013
      • im soooo with you. It is really getting me down. i am absolutely smashed

        pete wrote on October 26th, 2014
        • You guys totally just need some more potassium, sodium and magnesium. Make yourself a yummy drink with some crystal lite and add some diet salt (potassium chloride) and some Dead Sea salt (sodium and magnesium) and take a magnesium supplement. You’ll feel a world of difference.

          xoie wrote on April 7th, 2016
  30. I have also been easing my way into Primal (just bought the book too!) and with the exception of Memorial day weekend and this weekend (big party wedding) I’ve done pretty good, and have notice very little side effects during my transition.

    I do have one question though, since its my goal right now to be selected for my state police soon, how should I go about my workouts? Running is a big deal in the academy (normally 30-45 mins of running a day), and I probably shouldn’t be avoiding it as prescribed by the Primal diet. I did purchase (and began working out with) a kettlebell, and have been doing sprints, but can’t envision getting away with out running for extended periods of time. Can anyone help or provide some tips for me?

    NJSPHopeful wrote on June 7th, 2010
  31. Funny, I had suffered from this type of foggy-thinking syndrome for a couple years. Once I dropped the gluten grains from my diet my head cleared up.

    ToddBS wrote on June 7th, 2010
  32. Hi, everyone. This is Jessica, who inquired about the cognitive issues when switching to Primal eating. Believe it or not, my Primal journey began over a year ago when I first began eating Paleo-but there was still a considerable amount of fruit in my diet and it kept my on the carb hunger roller coaster (I think). Then I found Mark’s site and things got better. I was 100% Primal for about 6-7 months. The thing is, I had some weird metabolic thing going on (doctors found nothing) and was hungry all the time. I don’t know if it was recovery from years of high carb (“good” whole grains!) eating, severe chronic cardio recovery, calorie restricted diets for many years, or just randomness…probably some combination, but the caloric restriction probably wrecked my metabolism. Fortunately, it’s now back to normal. Despite keeping the carbs low (only from veggies and some fruit) during my first Primal attempt, I couldn’t get things to click. I don’t know if I was super sensitive to carbs and high sugar veggies like carrots??… So, I remained in the brain fog. I completely abandoned the Primal lifestyle, despite loving it, for various reasons completely unrelated to Primal (that’s another story!), but kept feeling the pull to come back. I’m happy to say that after my hiatus I’ve been Primal again for 3 weeks, but this time, no sugar-not even fruit or high-sugar veggies. Eventually I may add some fruit in, but until I get over the hump, I’m keeping the insulin spikes as low as possible. I am having severe carb/sugar cravings, so I’ve been trying to eat more fat and/or protein. It seems to be helping, but I’m really hoping I come out of the fog soon! I know this lifestyle rocks and I just want it to work! Definitely had the low-carb flu this time, though…chills, got a bad cold that went away in a weekend…just felt feverish. Yuck! My energy level has been way more consistent the past few days, but like Mark said in the post, the brain is lagging behind! Hoping it will catch up soon!

    P.S. I’m also wondering if maybe b/c I have an autoimmune disease if that could be a factor for the hard time I’m having switching over.

    Jessica wrote on June 7th, 2010
  33. Jessica. You know that would be a great question to put in Robb Wolf’s podcast!!!!!

    Christina wrote on June 7th, 2010
  34. Cocaine helped me through my early low carb days.

    thehova wrote on June 7th, 2010
    • That’s hilarious. You’re kidding, right?

      Jeanmarie wrote on June 10th, 2010
  35. It’s taken me about five months eating PB to finally figure out, at my activity level, about how many carbs I should eat. For a while I played around with less than 50 carbs a day, and I started to look really, well, frankly ripped for a 51 year old lady. But then at 108 lbs. I started to feel awful- weird dull headache feeling, NO energy, really tired- and I realized- Hey! You’re a horse trainer!@ You burn through a lot of energy every day!! Eat more carbs!! So now I do, and I don’t get all anorexic about an apple or a banana or a yam, and I feel MUCH better, and I am learning to listen to my body, and eat butter and bacon and grass-fed beef and tons of veggies and even new things, like chicken liver and beef heart. So I am a very happy 51 year old paleo-camper, and I feel like a kid again. Or even better, because now I have my own money.

    Samantha Moore wrote on June 7th, 2010
  36. You know, this sounds *exactly* like what happened to all the raw vegans. “After inital detox, your life will be amazing!” Except it wasn’t for most who tried the diet, and most quit. I wonder if the primal thing will suffer the same fate in 5-10 years. :(

    Joe, who is skeptical of all trendy lifestyles

    joe wrote on June 7th, 2010
    • well except low carb, high fat has already been around a lot longer than five or ten years and is only becoming more and more accepted and there are more and more people who have been doing it for decades, whereas the span of the average raw vegan life is what, five minutes? And they all look like cadavers? THIS is a sustainable WOE, raw vegan is NOT. Im not talking specificly paleo though, generally low carb, high fat, moderate protein, so it really cant be considered “trendy” lol.

      Marie wrote on February 4th, 2014
  37. In a low carb diet, more fat gets burned, of course.
    Fat is also used as storage to toxins. Maybe the fog and the low carb flu got to to with fat and toxins getting into the bloodstream and causing the fog.

    Just a thought I use when I feel foggy.

    Warm regards,


    Petra wrote on June 7th, 2010
  38. when I first started going Primal..I severely cut my carbs. this led to not feeling well at all. I introduced carbs back in at a level of 100-150 grams complex carbs. I slowly reduced it to about 50-80 grams complex carbs. I now function quite well on a 30-60 level. I am quite active and do exercise for over an hour 3 times a week, and keep active for the rest of the week. it works well for me.

    rik wrote on June 7th, 2010

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