I would have it as a guess that more than half of the people I have seen on the Ketogenic Diet have experienced to some degree what is known as Keto Flu or Low Carb Flu. Mostly a feeling of fatigue, slight headaches or nausea overcomes them. The symptoms of Keto Flu / Low Carb Flu usually occurs in the first two weeks of a person beginning a ketogenic diet and entering into ketosis. They can come and go if you’re not getting the right nutrition. 

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The other half follow what is recommended and replenish themselves with essential minerals and electrolytes that are being depleted. These electrolytes are flushed from their bodies as they rid themselves of the water retention and sodium their old high carb diets made them hang on to.

 What are the symptoms of Keto Flu or Low Carb Flu?

The symptoms of Keto Flu as you begin to restrict your carbs and enter into a state of ketosis varies from individual to individual. They differ in duration and severity, dependant on what high fat, low carb foods you include in your ketogenic diet and their mineral content.

The Most Common Keto Flu Symptoms Experienced are:

  • What is known as a Low Carb Headache,
  • Diarrhea
  • Fatigue
  • Weakness
  • Nausea
  • Dizziness
  • Low Blood Pressure
  • Brain Fog

What Causes Keto Flu / Low Carb Flu, Fatigue, Headache and other Symptoms of Ketosis?

Sugar and the brain keto flu low carb flu ketosis symtoms

Brains scans of healthy Normal Brain with Cocaine User and Obese Person Brain. Image Source Wikimedia Commons

Firstly I’d like to bring this away from the technicalities of minerals and nutrients for a second and get people thinking laterally about what they are embarking upon. Essentially when going into a Ketogenic Diet, Ketosis or most Low Carb Diets, we are breaking an addiction. Most western populations are drawn to carbohydrates, or put even more simply sugar! Sugar gives us an instant rush and satisfaction as it flows through our bodies, converts in our liver, into our blood, and on to our brain!

Sugars impact gives the brain the same reward system through a flooding of Dopamine that is the same seen in narcotics such as cocaine. It’s this high that keeps us wanting more. So we cannot expect to not have any symptoms of withdrawal when giving up a substance that behaves in a similar manner to us as narcotics. Fortunately, the withdrawal and cravings are not as extreme and are short lived.

As for the fatigue, weakness and other symptoms of keto flu and ketosis, what also happens when we go low-carb is that our kidneys cease holding onto the salt we consume. When our body ceases to rely on carbohydrates (because it no longer consumes them) we enter into ketosis, utilizing fats as fuel, and our metabolism changes.

While in ketosis, salt and water are more efficiently excreted. And of course, salt aka “sodium” is an electrolyte, not only is it an electrolyte, but it is also the bodies “Primary Electrolyte”. Sodium plays a huge role in our system.  This low sodium factors into why people experience keto flu symptoms while in ketosis.

So it’s little wonder bodybuilders preparing for comps complain so hard about Keto Flu Symptoms and have not much good to say about the Ketogenic Diet. In an effort to have their skin appear paper thin, stay vascular and show every crevice between their muscles they restrict sodium to the extreme.

Symptoms of Sodium Deficiency:

  • Fatigue
  • Muscle Weakness
  • Nausea
  • Diarrhea
  • Dizziness
  • Brain Fog
  • Headache
  • Low Blood Pressure

If you take a look at the symptoms of documented sodium deficiency, does it ring any bells? That’s right, the symptoms of sodium deficiency mirror keto flu symptoms while in ketosis as well as the symptoms of low carb flu on other carbohydrate restrictive diets.

Of course, some people reading this will be thinking, “We’ve been told our whole lives that salt is bad for us”. Well, that is true if you’re consuming high amounts of carbohydrates and your body hangs on to it, as carbohydrates need sodium to facilitate glucose production.

But like we stated earlier when in ketosis our metabolism changes and becomes more efficient at the excreting of water and salt, so it must be replenished through our diet. Which was never an issue with primitive cultures as they never paid any attention to watching their sodium intake, in fact, many sought it out through broths, blood and mineral rich springs for its feel-good properties.

Tackling Keto Flu Symptoms in Ketosis

By now I think you’re getting an idea of where we’re going with this. We always believe prevention is better than cure, but if you’re already suffering the symptoms of keto flu or low carb flu it’s not too late to incorporate these measures, and the great news is, you’re probably already in ketosis if flu symptoms such as a headache or fatigue are upon you.

  1. Up your sodium intake, replace regular salt with iodized salt (while no evidence that iodized aids while in ketosis or keto flu it has various other health benefits, most western cultures are deficient).
  2.  High fat, low carb soups or broths with enough salt to taste. Have a large mug in the morning or smaller cups throughout whether you’re suffering keto flu or not.
  3. You can try Sugar-Free Electrolyte good high-quality ones (read the label).
  4. Make the majority of your cooking oils and fat intake come from monounsaturated and polyunsaturated fats.
  5. Eat plenty of cruciferous vegetables, green and leafy.
  6. Take a multi vitamin as insurance, it’s possible to get all the bodies necessary nutrients on a keto diet. But I’ve been in the nutrition game a long time, and I don’t know anyone who gets all the nutrients the food gods recommend, I certainly don’t. Tip: don’t get all caught up in the Men’s Multi’s – Women’s Multis hype. They make minor adjustments that make not much difference to double their price.

In Conclusion

Keto flu symptoms, low carb flu or whatever you want to call it, comes down to two simple things a good majority of the time.

  1. Your withdrawal from sugar and carbohydrates.
  2. And a lack of Salt / Sodium, the bodies Primary Electrolyte. Usually out of fear people are too restrictive on it as they rightfully should be when eating high amounts of carbs. But as we said earlier, when in ketosis the body eliminates water and salt more efficiently, requiring salt intake to stave off fatigue and other keto flu symptoms. Don’t go crazy on it just make sure you get adequate amounts of sodium for your needs.


Resources: Body Recomposition by Lyle Macdonald whats causing muscle cramp 

We’ve read and reference often The Art and Science of Low Carbohydrate Living and we highly recommend you do too. It’s affordable and available in both paperback and digital versions.