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.
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!