All About the “Low-carb flu”

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What is “Low carb flu”?

If you’ve ever dramatically reduced your carbohydrate intake, you might have felt it already: it’s that first few days of headaches, brain fog, crankiness, and constant, dragging exhaustion. At some point, you know the magic is going to happen and you’ll start feeling like a human being again, but the transition period is really rough. It feels like having the flu (hence the name), only you’re not sick; you’re just cutting carbs. Low-carb flu can include any of the following:

  • You feel fuzzy and foggy, like your brain just isn’t working right. You might have a pounding or throbbing headache.
  • You’re exhausted, cranky, and irritable for no reason.
  • Going to the gym feels like an insurmountable challenge. If you do make it, your performance is completely down the drain.
  • You’re ravenously hungry, tearing into everything in sight.
  • You’re craving anything with carbs – bagels, pasta, pizza, sandwiches, mashed potatoes, candy…

So what gives? Isn’t Paleo supposed to make you feel better, not worse?

Yes it is – and yes it will, eventually. But for some people, there’s an initial period of adaptation while your body switches tracks. Here’s how it works:

At any given time, your body can be burning either fat or carbohydrates for energy, but given a choice, it’ll start with carbs. If you eat a mixed meal (say, a potato with butter), you’ll burn the carbs first, and then start working on the fat.

Metabolic flexibility is the ability to switch back and forth between carbs and fat for energy without a problem. This is how healthy humans are set up. If you eat a potato with butter, get up, and go along with your day, you’re metabolically flexible. First you burn through the carbohydrates in the potato; then you burn through the fat in the butter. Finally, several hours later, you notice hunger gradually increasing and get up to find something else to eat.

If you eat the potato with butter, and then an hour later you need some crackers because your blood sugar is tanking and you’re snapping at everyone in the room, then you have impaired metabolic flexibility. Your body burned through all the carbs, but the switch to burning fat is difficult – so it stores the fat and demands more carbs for energy. If you eat the crackers and just keep providing those carbs, the cycle keeps repeating (while you gain weight from all that stored fat). Dr. Eades has a good explanation of this here.

This impaired metabolic flexibility is clearly a problem – it’s a hallmark of diabetes and related metabolic disorders. Paleo is all about restoring metabolic flexibility, to avoid these problems, but unfortunately the low-carb flu can sometimes be a side effect of that. Initially, your body is going to throw an “I want carbs” tantrum – that’s the crummy, run-down, “low-carb flu” feeling. Eventually it’ll get the message and switch over to fat-burning mode, but sometimes it takes a lot of tantrum to figure it out.

Make no mistake: this stinks while you’re doing it. It’s not actually starvation, but it’s pretty close. But here’s the good news:

  • Low-carb flu is not inevitable: it doesn’t happen to everyone, and there’s a lot you can do to make it less miserable or even avoid it altogether.
  • It doesn’t last. Yes, it’s awful in the short term. But that short-term pain is a door to long-term gain.

Low-Carb Flu and Paleo

And now for the million-dollar question: do you have to put up with this to go Paleo?

No! For one thing, not everyone will get anything like the low-carb flu even if they do reduce carbs in their diet. Metabolically flexible people can adjust carbs up and down within a wide range and be just fine. It’s only people with impaired metabolic flexibility – people like diabetics, for example – who really get the worst of the “flu.”

Even for the unlucky ones, though, the misery isn’t inevitable. The first thing to remember about Paleo and the “carb flu” is that Paleo is not a low-carb diet. It can be low-carb, but it doesn’t have to be. Paleo is about eating the foods we’re evolutionarily suited to eat, not about any particular macronutrient ratio.

For people who are metabolically unhealthy, a low-carb version of Paleo can be very therapeutic, but you don’t have to go from 0 to 60 overnight. A better strategy is to step down gradually. First, try plugging a day or two of your current diet into any nutrition calculator online, to see how many carbs you already eat. Then start slowly pushing that number down while increasing fat and protein intake. Try to replace grain carbs with Paleo carbs as much as you can, but don’t be afraid to eat those potatoes! This will help your body adjust without the need for a brutal week of “carb flu.”

You can also do all kinds of other things to help make the transition easier, and reduce or avoid the “low-carb flu” altogether.Glass of water

  • Don’t reduce carbs unnecessarily. There’s no point to being low-carb for the sake of being low-carb! If you’re struggling with low energy and other flulike symptoms longer than a few weeks, maybe it’s not an adaptation period; maybe your body just does better with more carbs. That’s fine too. Don’t try to force yourself into a low-carb mold if you just weren’t cut out for it.
  • Get enough electrolytes. Salt deficiency and potassium deficiency can cause some of the same symptoms (especially exhaustion and exercise apathy); there’s no reason to make things worse!
  • Get enough fat. It is physiologically impossible for protein to be your primary calorie source. Your body will just stop metabolizing it, and you’ll end up starving even though enough calories are technically going into your mouth. Don’t do this! If you’re going to lower carbs, you absolutely must increase fat to match.
  • Exercise if you can. This review found that exercise was a great way to improve metabolic flexibility – but in the throes of carb withdrawal, a trip to the gym is probably the last thing on your to-do list, and that’s fine. Instead of forcing yourself through a workout when you’re falling asleep on the squat rack, put exercise on the back burner, and add it back in to maintain metabolic flexibility once the “flu” is over.
  • Drink plenty of water. Dehydration will just make the headaches worse, and it’s hard on your whole system.

Summing it Up

Not everyone gets the “low-carb flu.” In fact, many metabolically healthy people seem to skip it altogether, or else just get a very mild dip in energy levels for a day or two. So don’t go into Paleo assuming that you’re going to go through a week of horror before you get to the good part: it might not even happen!

On the other hand, people with impaired metabolic flexibility do often get a kind of “flu” from dropping carbs. This really stinks, but you can make it stink less by lowering your carbs slowly, getting plenty of water, salt, and fat, and giving yourself a break until it passes. Remember: Paleo is not a week-long fad diet; you can afford to take 2 weeks to ease into it for the sake of long-term sticking power. You also don’t have to do a low-carb version of Paleo if it doesn’t make you feel good; there’s no carb police hovering over your shoulder ready to pounce if you look sideways at a potato!

Ultimately, a hellish week of “carb flu” shouldn’t be the Paleo price of admission. You shouldn’t have to take vacation time just to change your diet. So if you’re in the throes of the low-carb blues, don’t just suffer through it; take a second to stop and think what you might do differently to make the transition less rocky and more sustainable.

P.S. Have a look at Paleo Restart, our 30-day program. It has the tools to let you reset your body, lose weight and start feeling great.

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