What Causes Keto Flu? (And 6 Keto Flu Remedies)

A strange set of symptoms affect low-carb dieters. These symptoms—a mix of headaches, fatigue, weakness, irritability, muscle cramps, and insomnia—have been dubbed “the keto flu”. While they are most prominent during the early days of a ketogenic diet, their fingerprints can be felt for a long time if the causes are not addressed.

The keto flu is mysterious in that most medical journals don’t mention it. Even the keto community can’t agree on what causes it. One article blames dehydration, another carb withdrawal, another still a lack of fiber. 

Just give it time is the boilerplate advice. I picture an avuncular GP making this utterance. A kindly old man who hasn’t read a scientific paper since 1983.

It is possible that your symptoms will improve with time. But if your keto flu is caused by low sodium, waiting will only make things worse. Sodium will continue to plummet and your body respond by decreasing blood volume and introducing dehydration despite your chugging water. When that is sustained for any length of time, your body will plunder your bones to make up the shortfall.

I don’t claim to have the secret cure for keto flu—and I’m not a doctor—but I am fairly certain of one thing: There isn’t just one cause. For instance, dehydration and low-sodium levels (both common on low-carb diets) cause a near-identical set of symptoms.

You’ll have to do a little detective work to solve your keto flu. I wrote this article as your guide. Here you’ll learn the most likely causes of keto flu, and—more importantly—how to fix them. 

What Is The Keto Flu?

The keto flu is not a tropical illness. It’s a catchy label for the set of symptoms linked to going keto.

The most common keto flu symptoms are:

  • Headache
  • Constipation
  • Muscle cramps
  • Diarrhea
  • Weakness
  • Fatigue
  • Irritability

With this set of symptoms, you can easily see why "flu" was the ailment selected to name this condition. These symptoms tend to occur within a few days of keto diet commencement, but this isn’t a hard rule. Some people feel lousy months into the program.

The keto flu is a product of change. When you first "go keto", you eliminate most carbs—a move that keeps blood sugar and insulin levels low. Low insulin then sends the ketosis bat signal, and the body shifts the primary source of energy at rest to a fat-based metabolism - be that from your plate or body.

But the human body is a complex and sensitive machine. Cutting out carbohydrates twists lots of dials, not just the fat-burning dial.

Broadly speaking, eliminating carbs causes keto flu, but there’s more to say on the topic. Let’s drill into specific causes now, then we’ll hit on remedies. 

Causes of Keto Flu

Rarely is there a single cause of any medical issue. Take heart disease, cancer, or Alzheimer’s as examples. These conditions have a panoply of causes scientists are still puzzling over. 

The keto flu isn’t on par with these conditions. It isn’t even a disease. But it does have a wide range of origins. Here are five. 

#1: Low sodium

The symptoms of low sodium—headaches, muscle cramps, weakness, brain fog—are basically the same symptoms as keto flu. More often than not, keto flu equals low sodium.

Sodium does more than make your eggs palatable. It regulates nerve impulses, fluid balance, and a variety of hormones. Without enough sodium, you won’t feel, perform, or sleep well.

For example, low sodium increases norepinephrine—a stimulating hormone not ideal for getting Zs. You also see low sodium plaguing elite athletes. They cramp up, lose cognitive function, and sometimes suffer brain damage.

Low-carb folks are at risk for sodium deficiency too. Allow me to explain.

When you ruthlessly restrict carbs, your pancreas reduces insulin production. We like this. Low insulin as a result of reduced carbohydrate intake permits your body to more readily access stored body fat. But the thing is, it also decreases sodium retention.

Right. When it’s circulating, insulin sticks its nose everywhere, like into your kidneys. Specifically, insulin tells your kidneys to retain sodium.

That’s why diabetics with hyperinsulinemia (high insulin) have problems with salt. All that insulin keeps them from peeing out sodium, which impairs their ability to regulate blood pressure.

Low-carb folks have the opposite issue. They pee out too much sodium. Combine that with lower dietary intakes of sodium (less chips, crackers, etc.) and you have a recipe for keto flu.

#2: Dehydration

Dehydration (losing too much water) presents similarly to low sodium. Headaches, cramping, fatigue, etc.

Well, guess what? The range of sodium in the blood which is conducive with staying alive is incredibly tight. If the body is shedding water it must shed sodium - and if it sheds sodium it must also shed water. You not only pee out more sodium on keto, but also more water. Same basic principle.

This doesn’t mean you should start hydrating like a beached manatee. Overhydration will dilute blood sodium levels and exacerbate low sodium symptoms.

Just drink to thirst. (Yep. That arbitrary advice that was given to you about "Drink X ounces of water per day" or "Chug a gallon of water every day" is just bad advice given by well-meaning people.

You can read more about how water can actually dehydrate you further here. 

#3: Carb withdrawal

Going off sugar is like going off a drug, and I don’t necessarily mean this metaphorically. When it comes to individuals who have a history of binge eating, or even just trouble with portion control, there is some evidence to suggest that their brains may process foods high in refined carbohydrates differently than those who do not have this issue. Admittedly, there is conjecture as to if the fMRI hits are related to the refined nature of the foods (hyperpalatable and hypercaloric) or if it is the volume of refined carbohydrates, but nonetheless - as the two are highly correlated, it may be difficult to separate them. 

Either way, "sugar addicts" not only behave similarly to substance abusers, but also show neurochemical similarities in their brains.

“Similar to drugs of abuse,” write the authors of one paper, “glucose and insulin signal to the mesolimbic system to modify dopamine concentration.”

Translation: Depriving yourself of carbs (which your digestive system breaks into sugar) deprives you of dopamine-driven good feelings. There's a reason so many comfort foods are a combination of carbohydrate and fat.

And so if you were eating a high-carb diet before keto, there’s a good chance you’ll experience keto flu symptoms from sugar withdrawal, however we define that term. Fortunately, this cause is the one most likely to be temporary.

#4: Less glucose to the brain

When you eat carbs, your brain runs primarily on glucose. But when you enter a ketogenic state, you lower your intake of glucose. As a result, there is a possibility that less glucose may be available to the brain.

That’s where ketones—your backup brain fuel—come in. Ketones fuel the brain with clean, efficient energy.

Still, the transition from glucose to ketones doesn’t always happen smoothly. This transition, researchers believe, may cause symptoms during the first few days of keto dieting.

Top 6 Keto Flu Remedies

Now that you know the causes of keto flu, the following remedies will make sense.  

#1: Use more salt

Keto flu is very often a case of low sodium. Fix the sodium and you fix the symptoms.

Do this by salting everything: meat, eggs, coffee, water and even salad. Don’t be shy with the salt shaker.

You might be worried that sodium will raise your blood pressure. Salt, it’s true, has become the bogeyman of heart disease risk. If you listen to the US government, you should limit sodium to 2.3 grams per day. 

But according to one paper, folks limiting sodium to under 2.5 grams per day actually had higher blood pressure than folks at higher sodium intakes. Even more convincing: Another paper from the Journal of the American Medical Association (JAMA) found that 5 grams of sodium per day (more than twice the government rec) was the sweet spot for heart health.

#2: Hydrate wisely

Dehydration can cause keto flu symptoms, so it’s important to drink enough water. But there are better and worse ways of hydrating.

If you over-hydrate, for instance, you’ll dilute sodium levels and worsen your symptoms. Do these two things instead:

  1. Drink to thirst
  2. Salt your fluids

Extreme cases (like sickness or elite competition) may require a more robust hydration strategy, but drinking salted water to thirst should prevent most cases of keto dehydration. 

#3: Try MCT oil

When you consume medium-chain triglycerides (MCTs), they travel straight to your liver for conversion to ketones. In other words, MCT oil increases your level of ketosis.

MCTs even work in the presence of carbs. You can skip the keto diet and still enter ketosis, though the benefits of doing so are not well-documented.

This is a bit speculative, but MCTs—by elevating blood ketones—may help your brain adapt faster to the keto-induced drop in glucose.

It's worth noting that MCTs, like all fats, are quite calorie-dense and nutrient-bereft, so if fat loss is your goal, it may be a bad idea to open the taps and chug MCT indiscriminately. Also, if MCT is a new supplement for you, it is wise to start slowly as they can introduce some gastric distress. If this is an issue, some of our clients have reported improved tolerance with MCT powders versus liquids.

#4: Eat non-starchy veggies

Non-starchy veggies should be the bulk of the volume of your keto plate. These plants provide valuable vitamins, minerals (like potassium and magnesium) and fiber that are often scarce on the keto diet.

For starters, try low-carb veggies like kale, arugula, spinach, broccoli, lettuce, and asparagus. If it has under 5 grams of carbs per serving, it’s a fine choice.

Quick caveat: Not everyone, especially those with existing gut issues, can tolerate lots of fiber. In these cases, a low-fiber diet can be therapeutic while the gut heals. 

#5: Consider carb cycling

Having carbs is not a sin.

On days when I am training heavily or will be on the mats in Jiu Jitsu for more than an hour, I tend to add more carbohydrates to my diet.

I don’t need carbs, per se. I just have better energy if I take 5-10 grams of glucose during intense sessions. If my training goes on for 2 hours, I may double this.

Another form of carb cycling is to pick 1 to 2 days per week and eat higher carb (say 75-150 grams) on those days. Of note is that I am not advocating for Snickers bars and Ice Cream. Favor healthy carbs like potatoes, tubers, and rice—not the refined stuff, even if it’s marked “gluten free.” I will admit that I'm not a fan of carb cycling as I think it can introduce as many problems as it resolves, but for more active individuals, more carbohydrate can often be tolerated.

Finally, keto is not the "single best diet" for everyone. Eating 75 to 150 grams of carbs per day may be a better approach for you. This is close to the approach recommended by Robb Wolf in his book Wired To Eat (my latest book) as part of his 30 Day Reset Diet.

#6: Supplement electrolytes

Diet and aggressive salting may not fulfill your keto electrolyte requirements. You might need to supplement, especially if you’re active, to prevent keto flu.

I generally recommend people consume 5,000 mg sodium, 1,000 mg potassium, and 300 mg magnesium - in addition to dietary sources. Hit these numbers any way you like. I used to make homemade blends, but now I just dump a stick or two of LMNT Recharge in my water bottle before exercise. 

Preventing Keto Flu

Keto flu is not a keto rite of passage. The symptoms stem from a number of causes that can be remedied.

Here are those remedies once more:

  • Use more salt
  • Hydrate wisely
  • Try MCT oil (strategically)
  • Eat non-starchy veggies
  • Consider carb cycling or increasing carbohydrates per day (if active)
  • Supplement electrolytes (I use LMNT Recharge)

I hope you found some helpful tips to help prevent keto flu and find success with your ketogenic diet!