The “Keto Flu” (also known as the carb flu) is a common symptom for those that first start keto, even seasoned users will still get it regardless of how keto adapted they are.


The symtoms when someone is first starting Keto is often very similar to having the flu or the common cold.  Switching to fat as the new source of fuel can be quite dramatic sometimes, and with time switching in and out gets easier and easier.

The signs usually can show up within 12-36 hours.  And would be based on how much glycogen / and carb based fuel is stored in your body – and how much you are still consuming in your new keto based diet.

The following are common symtoms that you may experience:

  • Headache
  • Irritability
  • Weakness
  • Difficulty sleeping
  • Poor concentration
  • Muscle cramps
  • Muscle soreness
  • Nausea
  • Vomiting
  • Constipation
  • Diarrhea
  • Dizziness
  • Stomach pain

Its commonly should only last between 12-72 hours either mildly to quite severely.  And its often the first and largest hurdle to keto, so don’t give up quite yet – stay focused – remember you are doing this for your health, and sometimes transitions can be a bit difficult.


Want to ease those keto flu symptoms to reach keto heavenly plains – check the following points we’ve detailed below.

Stay Hydrated:

Keto can cause you to rapidly lose your water stores – often due to inflamation in your body decreasing – and is part of why you drop a lot of weight right at the beginning.  Make sure you drink enough water to replenish your fluids, it eases toxins being flushed from your body – and if you are getting flu like symtoms (often including headaches) hydration is key to make this as least painful as possible.

Science: This is because glycogen (energy ready carbs) binds to water. When carbs get flushed out – they take all the water with them – and thus your body will loose more than a normal amount of water that you might be used to.

Exercise intensely (once) in the first 12 hours:

Carbs are stored in your body (as glycogen) before you commence a keto diet.  To speed up the transition its often suggested that doing an intense session of exercise (anabolic / HIIT) will help burn all these carbs and force the body to start using fat for fuel.

Caution: Some people do have mixed reactions with this method, often either finding it makes flu like symptoms worse, where as for others it reduces / irradiates them.

Don’t do intense exercise:

A bit strange to give this advise directly contradicting the point above – however it should be said that for some people the transition from carbs to ketones can be difficult and letting the body slowly switch will help ease them across from one state of energy use to the other.

Light Intensity Steady State (LISS) / light activities like walking or yoga (article on recommended yoga styles for fasting / keto here) are ok – but make sure you don’t stress yourself.

Replace Electrolytes:

When transitioning into using ketones for fuel, the body releases a lot of water.  With this they take a lot of electrolytes and salts with it.

Adding a little bit more salt to the food you are having will make a big difference is easing your symptoms.  I’d go as far as saying this is probably the most common issue and users will almost immediately within a few hours report to be feeling much better.

Potassium is hard to come by with some select keto foods so the importance to try and include these in your diet is quite important.  Dark green leafy vegetables / particularly cruciferous vegetables and avocados are the ideal way to ensure you are maintaining a healthy balance or all your nutrient and electrolyte needs.

Get Adequate sleep:

With the dramatic hormonal shift from carbs (glycogen) to fat (ketones) there are quite a few adjustments that are happening around the body.  Getting a little more sleep than normal will make a big difference for you.  This goes along with resting rather than distracting it with other tasks that slows the bodies process of shifting across to ketosis.

Reducing caffine intake can help allow you to sleep easily. However if your goal is autophagy for fasting purposes – coffee can also help speed up this process – we have a great in detail article about that here: Is black coffee ok for Fasting?

Check your diet is actually Keto:

Its well known in the keto community if you stay around long enough that a lot of new people often will not even reach ketosis or only do so for short periods of time.  The main reason: They are still eating too many carbs.  You just need to make sure that your ratio of food intake is:

  • 75% Fat
  • 20% Protein
  • 5% Carbs

These numbers are not solid however its the most recommended guide for people.  With time you can then start to push these numbers a bit and find that you can actually eat more carbs than usual.  The recommended would be less than 20g.  However there are Keto dieters that can do 50g a day.  If you are not sure how many carbs are in something – you can check online for your fresh foods, or the nutritional label on the back will have it all broken down in detail for you.

To make this process even smoother, if you can try and reduce ALL carbs to just fat and protein – such as a carnivore diet – this will then help ease your keto flu symptoms even further and kick you into keto much faster.

If you are worried about missing sugar, bread and pasta – its often reported – and was the same case for me – that these cravings will go away – so don’t stress, flex your psychology a bit – and know that in a day or so all of this will disappear.

How long does it last

In general symptoms might last anywhere from 12 to 72 hours – assuming you are following all the advice above.  It’s also common to experience flu symptoms when transitioning back to carbs.  Just hold tight and be patient, the rewards are well worth it.

If it starts to go longer than a week – its recommend to speak to a doctor or nutritional coach to find out if the symptoms are from other issues or illnesses that you may have.

Who shouldn’t do Keto

Depending on where you are in life or present medical situation it may be best to put Keto on the backburner for a little while longer.

Women that are pregnant or breastfeeding are recommended not to do Keto.  Studies have shown that having ketones in your system can not completely nourish a unborn child resulting in undeveloped neurons in the brain and resulting in lower IQ scores – this also goes for breastfeeding babies – the full amount of nutrients required hinders the babies developing brain.

Children and teens are advised to not do Keto.  Being highly active and still developing and growing exhausing themselves of fast acting energy sources like Glycogen will be quite difficult.  Its also very difficult to convince kids not under a parents watchful eye to not eat lollies and carb based snacks while at school – and likely result in them feeling pretty average and putting on weight rather than reaping the benefits of ketosis.  If this is done it is highly advised to do this under the super vision of a health care professional.

Health conditions relating to critical detoxifying organs such as the kidneys, liver or pancreas are advised to speak to a medical professional as well.  When these organs are functioning at very low levels certain stresses with the hormonal shift can cause issues.  Keep in mind Keto and even fasting with autophagy can help to start healing these – so don’t rule it out.  Just make sure to get professional advice.

Diagnoses type 2 diabetes and prediabetic clients also should be very careful because Keto directly changes the way energy is produced in the body from Insulin to Ketones.  Ketosis is well documented to help reverse and even cure diabetes with Dr Fung claiming that 100% of his type 2 clients have been cured from prolonged water fasts (which involved the body being in states of deep ketosis for long periods of time).


Just keep in mind that the keto flu (carb flu) is just a brief window for your body to adjust to using ketones rather than glycogen to power the body.  Hang in tight, refer to the information above to ease your symptoms, and you’ll be there i no time, sharper, focused, satiated and losing weight.

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