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Does the Ketogenic Diet have negative side effects?

The short answer is most likely, in the short term!  But let's focus on the long answer to get a better understanding of why this might happen.

The reality is that ANY dietary change is going to give you side effects when you first make the change.  It doesn't matter if you are going to a vegan diet, or high protein diet, or a low fat diet.  The ketogenic diet is no different.  Your gut and your body will need time to adjust to the diet.

What are the Initial Side Effects on the Ketogenic Diet:

1.    Carbohydrate withdrawal (AKA “The Keto Flu”):

As you stop eating carbohydrates, your body will go through carbohydrate withdrawal symptoms.  They may show up anywhere in the first few weeks of keto, and may last anywhere from 1 to 2 weeks (although usually experienced in the first 3 days).  These symptoms include:

  • headaches,
  • fatigue,
  • dizziness,
  • brain fog,
  • nausea,
  • irritability, and
  • cravings for carbs

Why do these happen? For a few reasons:

a)    Your body is not yet "keto-adapted", a term meaning you are not very good at using fat as fuel yet.  So as you limit the carbs and eat high fat, the fuel (fat) is there, but the engine might be a bit slower to process this new fuel (hence the potential for headaches, foggy brain, and dizziness).   Keto Adaptation can take anywhere from 6-8 weeks (not including physical performance which may take 6 months ore more!).

b)    Plus, our bodies go through the physical (and very real!) symptoms of Carbohydrate Withdrawal (yup, similar to weaning off morphine!).  You will be irritable and have cravings for carbs.  It should only last a few days, but, yes, those days will be unpleasant.

c)    Additionally, when we eat carbohydrates, our kidneys respond by holding on to sodium and as a result, also water.  When we start a ketogenic diet, the kidneys are able to let go of the sodium and water – the first few pounds people tend to lose in the few days/week of starting the ketogenic diet!  While this is just water weight, it goes to show that your body is adapting to the new diet.  This said, because of the lost water, it is very easy to get dehydrated and not eat enough salt, which can also result in these side effects. You will also find you need to urinate more often on the ketogenic diet, especially as your body adapts.

The best way to deal with the Keto Flu: Stay hydrated! Drink plenty of liquids (especially home made bone broth or use bouillon cubes) with lots of added salt and electrolytes. You want to be eating 6-7g of salt (1-1.25 tsp) per day.  If you find yourself dizzy or having a headache, put ½ tsp salt in water and drink it.  You should feel better in 30-60 minutes. Eat avocado for potassium.  Did you know that avocado has more potassium than bananan?! Yup, just a random fact... ;) And aim to eat 2-4 cups of green leafy vegetables daily for your magnesium needs.

NOTE: if you are on any medications, IT IS CRITICAL TO CHECK WITH YOUR DOCTOR before starting on a ketogenic diet, as well as to rule out that side effects you are experiencing are result of a new medication dosage requirements.  Especially when it comes to diabetes and blood pressure medication, it is possible you are experiencing low blood sugars or a drop in blood pressure. Go to your nearest hospital if you feel unwell and are on medications, to rule out any medication related complication.  

 2.    Constipation:

Starting any new diet will cause a change in your gut health and bowel movements.  It just will.  Changing what goes in, changes what comes out!  As a result, a very common side effect is constipation.  You may notice it immediately, or not until weeks 3 to 7.  Hydration will play a huge role in whether and to what extent you get constipated.  It’s important to note that you may need help to get past the constipation! No need to 'tough it out' if you are pooping rocks... Just get help. You can either go to your MD to get a prescription for a stool softener, or pick up something like “laxaday” or “milk of magnesia” to help the stool pass.  My suggestion for the over the counter meds, is to start at the lowest dose and see how you react.  Increase if necessary.  Milk of magnesia has magnesium in it and may help with electrolyte balance as well as reducing muscle spasms and improving sleep.

3.    Muscle spasms:

If you are experiencing muscle spasms, it means you are low in magnesium. (Especially if you have issues with your blood sugars). Take a supplement of 400mg magnesium.

4.    Insomnia:

Some individuals may experience insomnia when first starting keto.  Taking a magnesium supplement (400mg/d) may help.  Try to optimize your sleep by getting out into the sun as much as possible daily (to help reset your circadian rhythm), make sure that your bedroom is dark at night (block out curtains), and try to avoid screens approximately one hour before sleep (alternatively: check that ‘sleep mode’ is on your phone/ipad/android/tablet – in brightness settings; for the TV, wear orange tinted glasses to block out the screen’s blue light – from amazon.ca).

 5.    Frequent Urination:

As a result of the kidneys releasing excess water, you will find that you need to urinate far more often than you had in the past. Try to drink plenty of water during the day and less at night so that you do not find yourself waking up at night to need to urinate.

6.    Decreased physical performace

As you can imagine, if you put unleaded gas into a diesel engine, the car is not going to run optimally.... compare this to your body!  You are physically fit, doing cardio of choice (jogging, running, cycling, swimming, etc), and lifting weights... your body is adapted to its fuel source - carbohydrates!  It knows how to use the fuel, it gets the energy to the cells as you need them, you are pushing personal records - this makes sense!  Now, when you move to a ketogenic diet where you are changing the fuel source at the cellular level, your body will naturally struggle in the beginning!  It takes time for your body to build fat receptors in the gut, it takes time to build mitochondria in the cells to burn the fat!  So during your initial fat-adaptation, you will definintely have lower physical performance... why? because while you have the fuel in your body (whether from eating fat or from the fat stored on your body), your body needs to learn how to use the fuel!  Give yourself (depending on your level of performance) anywhere form 3 to 6 to 12 month to get back to your previous personal records, and then see yourself make new ones!

7. Heart Palpitations:

During the first 6 weeks of the ketogenic diet, it is possible you might experience heart palpitations – your heart beating fasters, or in some cases, stronger. This usually due to being dehydrated, so make sure to drink plenty of water and sodium.

Heart palpitations may also be a result of low blood sugars (only if you are taking diabetic medications which lower your blood sugars) or low blood pressure (if you are on medications).

Please check with your doctor that you have no underlying cardiac condition and always get any heart palpitations checked out to rule out any other underlying cause. If the heart palpitations are a result of low blood sugars or blood pressure, work with your doctor to lower your dosage, and have them monitor your closely.

Note: If you are struggling with insomnia, muscle spasms and constipation, please only take 400mg magnesium. You do not need to take one dose per side effect.  Additionally, if you are struggling with these side effects, please see a low carb health professional to help you get through them as pleasantly as possible.
For more information on potential side effects, please refer to the DietDoctor.com.



How did this Registered Dietitian find the Low Carb High Health Fat Diet?