Everything you need to know about the Keto flu and how to combat it

The Keto Flu

The Keto Flu

Have you recently started the keto diet and noticed that you feel almost as if you've got the flu? Headaches, lethargy, irritability, nausea, mental fogginess, muscle aches, the list goes on. While this can be a concerning experience out of the gate, the “keto flu” is really just a sign that your body is heading in the right direction.

After all, you’re switching to a diet that goes against the grain of what your body has been accustomed to for decades! We are raised to believe that starchy and sugary foods are what “energize” us and keep us going. Naturally, years of eating candy, fruit juice, cereal, bread, pasta, and other carb-heavy foods means your body needs to go through a bit of a transition once you adopt the keto lifestyle.

If you’re currently experiencing symptoms of the keto flu, don’t worry! The keto flu is temporary and it will pass on its own. If you find that the keto flu symptoms are impeding your daily life, there are some nifty tricks to help treat the keto flu so you can get through it quicker and stay on track. Read on to learn more about what causes the keto flu, what the symptoms are, and how to work through this peculiar “illness”.

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What is the Keto Flu?

Usually, the first 2-3 weeks of starting the keto diet are the most arduous since this is like the “initiation phase” for your body. Cutting carbs and eating more fat means your body is forced to switch from being a sugar-burning machine to a fat-burning machine.

In reality, switching from a carb-rich diet to the keto diet is tantamount to changing from regular unleaded gasoline to premium gasoline. Fats are a superior source of lasting energy for the human body and, like premium gasoline, they will get you further per molecule burned.

However, the transition to the keto diet can bring about symptoms as your body adjusts to this new “fuel source”. The onset of keto flu symptoms generally occurs a few days after you establish and maintain ketosis. For most people, this comes out to be 1-2 weeks into the keto diet.

The keto flu isn’t an official medical condition, nor has it been studied much since it’s a fleeting experience that resolves fairly quickly in most cases. Yet, the keto flu is a cause for concern for those new to the ketogenic diet and those who are considering making the switch.

In fact, the colloquial term “keto flu” came to be because the symptoms are somewhat synonymous with those of influenza, less the puking. (Note: If you’re puking after a week on the keto diet, you may have the “actual flu” or food poisoning.)

As such, it’s not clear what exactly happens physiologically that causes the keto flu, but hypothetically the symptoms are likely the result of “withdrawal” from sugar and possibly electrolyte loss/dehydration. From a scientific standpoint, this makes sense since sugar has been shown to produce effects in the brain that are similar to cocaine, and carbohydrates help your body retain fluid.1

If you’ve been a regular coffee drinker for years, then you know all too well how it feels to go even 3-4 days without any caffeine. Hence, the keto flu is somewhat like a drug withdrawal.

So, what are the symptoms of the keto flu? More importantly, what can be done to treat them?

Keto Flu Symptoms

During the first few weeks of the keto diet, your body is adapting to using fat for energy and being in ketosis. The benefits of ketosis are myriad, including2:

  • Boosting mental performance and protecting the brain
  • Reducing the risk of type-2 diabetes and insulin resistance
  • Supporting weight loss
  • Helping control appetite and food cravings
  • Fighting inflammation
  • Increasing energy

Sounds pretty awesome, right? The catch is that your body doesn’t operate like an on/off switch, and it needs time to acclimate to this 180° change in dietary habits. As such, the keto flu is basically sugar withdrawal and the symptoms are often flu-like.

The most common keto flu symptoms include:

  • Lightheadedness
  • Brain fog
  • Headaches
  • Irritability
  • Cravings for sugary food
  • Lethargy
  • Stomach discomfort
  • Muscular aches
  • Trouble sleeping 

Don’t let these symptoms of the keto flu scare you, though. They tend to be more subtle than what you experience if you have influenza. To reiterate, it’s apropos to compare the keto flu to drug withdrawal, particularly a psychoactive substance like caffeine. (This is why some people refer to the keto flu as the “sugar flu”.)

How Long Does the Keto Flu Last?

For the majority of keto newcomers, keto flu symptoms subside within a week. In rare cases, the the symptoms of keto flu may last 3-4 weeks (this is more likely to be the case if you used to eat a diet containing high amounts of sugar/carbs).

The good news is that the keto flu doesn’t happen to everyone who goes keto; plenty of people experience no adverse effects when they switch to a low-carb lifestyle.

How to Treat the Keto Flu

For those of you who do go through the keto flu, there are some practical tips you can implement to help treat the symptoms.

Supplement with Electrolytes

Switching to the keto diet means you need to cut out some of nature’s richest electrolyte sources, notably sugary fruit and starchy veggies.

Thankfully, you can still get your daily electrolyte fix either by using a keto-friendly electrolyte supplement or even adding pink Himalayan sea salt to your drinker water. Mineral/spring water is another great source of electrolytes, particularly magnesium. Some people will also drink bone broth throughout the day since it generally contains a high amount of sodium and potassium.

Drink Plenty of Water

Being dehydrated can make anyone feel borderline ill, regardless if they’re on the keto diet or not. Moreover, staying hydrated is key for easing and avoiding headaches that the keto flu may bring on.

At the bare minimum, you should aim for about one ounce of water per every kilogram that you weigh. One kilogram is equal to 2.2 lbs, so if you weigh 160 lbs you should drink no less than roughly 75 ounces of water per day. Increase your intake if you are a highly active person and/or you work in a hot environment.

Also, be wary that drinking a lot of coffee can actually dehydrate you since caffeine is a diuretic. If you’re the type to start your day with a cup of joe, drink some water along with it to help offset any fluid loss.

Eat More Fat

If you find your sugar cravings to be through the roof, eating more fat is prudent. Fat is the most satiating macronutrient and also what helps your body create ketones, thereby reducing hunger.3

Don’t be afraid to add some extra MCTs to your coffee, or make some fat bombs that you can indulge in whenever your sweet tooth kicks in.

Modify Your Carbohydrate Intake

If the previous tips don’t seem to be reducing your keto flu symptoms, it might be beneficial to incorporate a few starchy carbohydrates in one of your meals during the day. If you’re a regular gym-goer or someone who exercises daily, you could try adding 20-30 grams of carbs to your pre-workout or post-workout meal. Good carb sources, in this case, would be things like bananas or sweet potatoes since they are rich in minerals.

Do this for a few days and see if the keto flu symptoms become less intense, then slowly transition to a full-on keto diet.

The Keto Flu is Temporary - It Will Pass!

While the keto flu might have you reconsidering the carb-less lifestyle, remember that it’s merely an ephemeral transition phase. If you stick to your guns and push through the keto flu, you’ll come out on the other side and never look back.

Think of the keto flu as being a slight bump on the road of your keto journey. It might rattle you a bit, but the benefits of staying the course are well worth it. 


  1. Ahmed, S. H., Guillem, K., & Vandaele, Y. (2013). Sugar addiction: pushing the drug-sugar analogy to the limit. Current Opinion in Clinical Nutrition & Metabolic Care, 16(4), 434-439.
  2. Hashim, S. A., & VanItallie, T. B. (2014). Ketone body therapy: from the ketogenic diet to the oral administration of ketone ester. Journal of lipid research, 55(9), 1818-1826.
  3. Newman, J. C., & Verdin, E. (2014). Ketone bodies as signaling metabolites. Trends in Endocrinology & Metabolism, 25(1), 42-52.


Article By: Elliot Reimers

Elliot received his B.S. in Biochemistry from the University of Minnesota and is currently working on his M.S.in Pharmacology & Toxicology at Michigan State University. He has been a freelance science writer for over six years, with an emphasis in nutritional biochemistry, exercise physiology, and pharmacology. As such, he is thoroughly passionate about helping others comprehend scientific research and understand the biochemical mechanisms that underpin human health, performance, and longevity; he hopes that such knowledge will help people make smarter decisions about what they put in their body. In his free time, you can most likely find him hoisting barbells, hiking the mountains of Colorado, or working on his supplement science website - www.supplementuniversity.com.

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