When does keto flu hit?

In short, keto flu will typically hit within the first 24-48 hours of starting a ketogenic diet, although it can start later. The onset is dependent on when your body starts breaking down glycogen for energy.  In order to understand when it happens, it is a good idea to understand what keto flu actually is.  Hint, it is not the flu or anything related to an actual sickness. 

For a full discussion, see “What is Keto Flu“. In brief, it is a set of symptoms that mimic aspects of the common flu, such as headache, constipation, muscle cramps, diarrhea, generalized weakness, light-headedness, and brain fog. Keto flu is very common, but it can be avoided to some extent. But to understand how to avoid it, we have to know why it happens.

For a more detailed discussion around the physiology changes that occur during the different phases, see: “What happens to the body during keto?”.  In short, as your body burns through its carbohydrate stores (glycogen), a lot of water is released and eliminated.  This is why people tend to lose a lot of weight in the first week on keto… most of it is water. 

In fact, for every gram of glycogen burned, two to four grams of water will be released and eliminated (depending which study you go by)!  This also depletes your sodium levels and can impact potassium and magnesium levels as well.  In essence, keto flu is a combination of dehydration and electrolyte imbalance.  That being said, there is some carbohydrate influence as well.

During induction and transition, your body is try to adjust to not having enough energy.  It had been functioning on carbohydrates and it is not yet efficient at living off fat.  Part of the fat adaptation process is the upregulation of genes make the body more efficient at using fat as a fuel source.  However, until that occurs, your body is trying to run off of two fuel sources.  This doesn’t work well, so your body, especially your brain, can become foggy and fatigued.

To overcome this, some people recommend using exogenous ketones to help increase the ketone levels in your body until the liver can get acclimated and producing enough ketones on its own.  See “Should I take exogenous ketones?” for more discussion and why we don’t recommend exogenous ketones for ketogenic diets. However, when keto flu hits, it could be the one time when exogenous ketones might help. That being said, they should be discontinued after day 4 or so when the body has adapted enough to self-stabilize your blood sugar.

Above all other treatments, the best advice to is to stay very well hydrated, make sure you are getting enough salt in your diet (2 cups of bone broth per day can satisfy this need on both counts), and consider using electrolyte supplements to cover the potassium and magnesium loss.  In fact, due to the effects of the ketogenic diet on kidney function, you will probably need to maintain higher levels of salt intake than you are used to as the kidneys get more efficient and more sodium is lost.  Again, 2 cups of bone broth a day should suffice.

In fact, due to the effects of the ketogenic diet on kidney function, you will probably need to maintain higher levels of salt intake than you are used to as the kidneys get more efficient and more sodium is lost.  Again, 2 cups of bone broth a day should suffice.

One note of caution… if you are experiencing keto flu after two weeks or so on the diet, something is wrong.  Speak to a ketogenic nutrition specialist or a medical provider as you may need to monitor lab values during your transition phase.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.