Medically Reviewed by Dr. Bryan Seigel D.C., P.L.C.
You’ve started the keto diet, and kept your carbs under 20g a day for several days in a row. Great job!! So why do you feel like crap, and how can you make this headache go away? Dear friend, you have begun to experience the keto flu. But fear not! We can fix this, and it’s quite easy. Let’s engage in this battle with the best weapon in our arsenal: science!
What is the keto flu?
It’s important to know that the keto flu has nothing to do with the seasonal flu. The seasonal flu is a virus and produces symptoms like fever, congestion, and body aches, among others. The keto flu, on the other hand, produces fatigue, brain fog, headaches, and mood swings. You might also experience wicked sugar cravings, insomnia, muscle cramps, and altered bowel habits. The keto flu isn’t contagious and it isn’t caused by a pathogen like a virus or bacteria (or a brain eating amoeba).
Two things are contributing to feeling like you got run over with a school bus. The first, which is both the largest contributor to your sensations, and the easiest to fix, is electrolyte loss. Electrolytes are essential for the conduction of particular signals between cells. They work in pairs, antagonistically, or having opposite functions.
Electrolytes, you say?
These are the minerals that must be constantly replenished for energy and fluid balance, as well as proper nerve and muscle coordination. Sodium, most commonly called salt, works with potassium to maintain optimal fluid balance. Sodium is in circulating fluid, like blood, where potassium is inside the cells. (Fun fact! There is a sodium-potassium pump in the membrane on the surface of most cells that uses about 30% of the ATP, or cellular energy, we generate!) Calcium and magnesium are the other pair. Calcium is needed to strongly contract muscles, where magnesium is needed to relax them (and perform about 300 other functions in the cell besides).
The problem is that electrolytes get used up and excreted. Remember the first few days when you were truly in ketosis, and you had to pee 50 times? All that urine translates to massive electrolyte loss. You don’t need to hold on to the excess water, but you do need to replace the minerals or you start getting fatigue, headaches, and cramps. Sound familiar? It’s common enough to see electrolyte loss in non-keto folks, but the effects take longer to manifest in such dramatic fashion since they have more of a fluid-retention buffer.
The fix is easy: drink your electrolytes in a tasty beverage! An electrolyte drink mix will have you feeling on top of the world in, no joke, 45 minutes or less. Electrolytes get into circulation pretty quickly. Electrolytes are ideally replenished daily, and a little more frequently if you’re an athlete or otherwise sweating them out. Advanced players will start taking electrolytes at the same time as they start the keto diet. In a pinch, try pickle juice, or add about a quarter of a teaspoon of salt to something like keto lemonade. Some people have done shots of soy sauce in desperation and it’s not a bad idea. Bone broth is also a great idea since it’s so rich in minerals, and more stores are carrying high quality brands so you don’t have to make it yourself.
If you’re very clever and have great friends, instruct them to ask you “how much salt have you had today?” in response to any time you complain of feeling tired, run down, or just not feeling like yourself.
What’s the other reason?
The second reason you’re feeling less than your best is that you’re keto adapting. You’ve run on glucose for your whole life and you’re switching to a completely different fuel source. It takes time for all of your cells to reorient. You’ve cut off the sugar supply so you’re learning how to make and burn ketones to live off of. This part takes a little longer, but you can speed it up and make it less miserable.
Counterintuitively, while your energy balance is being challenged, try to challenge it a little more with physical activity. This is a homeostatic stress, the kind of thing where it’s not going to kill you but it will make you stronger. Consider it metabolic training. Even if you’re just walking a little more each day, increased activity speeds up adaptation.
The other thing you can do is increase intake of fats that are easily broken down into ketones. The absolute best in this arena is MCT oil or powder. Medium Chain Triglycerides skip digestion and head to the liver, where they get turned into ketones to be sent all over the body. Pro tip: start slow. Like most things on keto it takes a little adaptation. Too much too fast causes unpleasant digestive effects.
Are you eating enough?
Keto has the rare honor of being a diet that makes you feel full. Meals fill you up faster because protein and fat are satiating nutrients, so your brain gets the signal to stop eating. This is a perk because, if you spontaneously decrease your calorie intake while still feeling full, losing weight is way easier. It’s a double edged sword though: decreasing calories is yet another thing your body needs to adapt to, and this can lead to headaches and fatigue, as well as brain fog and moodiness.
It may sound counterintuitive, but you might need to eat a little more in your adaptation phase. Try adding a little more protein and veggies to your meals and see if that doesn’t do the trick. Keep an eye on your fat intake too: you might be eating a lot less than you think. Your best bet is to plug your foods into a tracker like Cronometer or MyFitnessPal to see what a typical day looks like for you, and make adjustments as needed.
Don’t forget hydration!
While you dial in the best ways to make keto work for you, it’s important to remember the basics. Part of that is drinking enough water each day. A ketogenic diet supports healthy water balance in the body, meaning you won’t hold on to extra water weight like you might on a higher carb diet. Water is used and excreted more efficiently, so you must be mindful that you’re getting enough. Dehydration causes identical symptoms to the keto flu, and for some people it’s entirely responsible for them feeling crappy.
Every person is different, but a good starting point is 64oz of water with added electrolytes every day. If you don’t drink much water now, that might sound like a lot, but it’s an easy habit to get into. Carry around a 32oz water bottle and drink throughout the day, making sure to fill and empty it twice, not just once. If you have more mass, you’ll need more water. You’ll also need more if you’re working out or in hot and dry weather.
What is the keto flu? You now know that the two primary causes of the keto flu are electrolyte loss, and adaptation to using ketones as fuel. The first is easy to fix, and the second will pass with a little time. Too few calories and not enough water are also culprits in the keto flu. Many people quit keto in the first few weeks because they don’t understand why they aren’t feeling great, when they just haven’t been given good enough information and help. We want you to be empowered to succeed, and strive to equip you with the tools you need to do so. You’ve got this!