Fasting Basics: When to Stop Your Fast

By Jason Fung, MD

Are you paralyzed with thoughts of mouth-watering bacon? No matter what you do you just can’t stop thinking about how desirable it would be to sink your teeth into that juicy steak you’ve been daydreaming about?  It’s low carb and even keto, right?  Should you give in and break your fast since this is a ‘safe’ food selection? FINISH YOUR FAST!

For most of us, our biggest issues when it comes to fasting is mind over matter.  Sometimes our mind can feel like it’s a hurdle more challenging to climb over than Mount Everest.   But with consistent effort we can change our thought processes within a matter of weeks (more on the behavioural challenges with fasting in my next post).

But, when should you call it quits during a fast?  In our last post on Fasting Basics, we talked about some side effects of fasting, such as headaches and flu like symptoms.  More often than not it’s okay to push through those side effects as long as you consult with your doctor and make sure there isn’t anything more serious going on.  However, there’s one symptom that should be taken very seriously: nausea.  If you feel even the slightest bit nauseous during a fast, you should end your fatst immediately.

Nausea usually occurs because you’ve become too dehydrated.  Either your electrolytes have become too depleted or the concentration of ketone bodies (fuel source produced by burning fat) in your blood has become too high.

Does this mean you should drink more water?  No, not necessarily.  You should only drink if you feel thirsty.  There is no ideal number of ounces of liters of water you should consume each day.  If you feel thirsty, drink.  If you don’t, then don’t drink.  Overhydration is just as problematic as dehydration.

So, how can we stay hydrated if that doesn’t mean we need to drink water every second of the day?  Follow these tips below to make sure your only problem while you’re fasting is the thought of a yummy meal ahead.

Supplement with electrolytes

Problems with electrolyte imbalance is often experienced when someone with elevated insulin levels or metabolic syndrome start to fast (hyperinsulinemia or insulin resistance). When we start to fast our insulin levels start to fall quite dramatically.  This drop causes a signal to be sent to the kidneys to release excess water.  But often, we lose extra electrolytes, particularly sodium, too.

What can we do to help prevent this from becoming problematic:

  • Have a cup of homemade bone broth or a low carb vegetable broth
  • Have some pickle juice either straight or diluted in water to taste
  • Add 1-2 TBSP of sole to a cup of water
  • Take some fasting drops throughout the day
  • Take a pinch of salt and place it on your tongue

If you’re someone who doesn’t have issues related to high insulin levels, and you’re not coming off a carb binge, then you’re less likely to experience these issues.

Expert tip: it’s more important to be diligent with electrolytes during the first 72 hours of an extended fast because that’s when you’re going to see the greatest drop in your insulin levels.


If you feel hungry, try having a cup of water first

We often mistake thirst for hunger because we’ve become so out of tune with our bodies.  And when we’re fasting, we expect to experience intense hunger, so we just ignore it.  This is how thirst often becomes ignored.  As a result, the concentration of items in our blood can become too high, which may lead to problems like nausea.  The same is true if we overhydrate with water and the concentration becomes too low.

As we burn body fat we produce an alternative fuel source to glucose called ketone bodies.  Usually the presence of ketone bodies in our blood is a safe and welcomed thing, especially if we’re trying to lose body fat.  But just like everything else, too much of a good thing can be a very bad thing.  If the concentration of ketone bodies is too high in our blood, then we may start to feel nauseous.

Follow these suggestions to make sure you aren’t mistaking thirst for hunger:

  1. If you feel hungry, drink 1 cup of water and wait 30 minutes
  2. Go do something instead of sitting and staring at the clock
  3. Ask yourself: do I still feel hungry? More often than not the answer is no.

Expert tip: you should even do this on eating days between meals when you’re tempted to snack on nuts and cheese.  Remember it’s not just what you eat but it’s also when you eat that determines whether or not you’re healthy and will maintain your weight.

Always remember you can break your fast if you feel unwell for any reason, not just nausea.  You can always start your fast when you start to feel well again.  Listen to your body and seek medical attention immediately.


  • Megan J. Ramos


By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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