Fasting Basics: What to do if you are struggling to get through your fast? Part 3

By Jason Fung, MD

In the first two parts of this series on fasting struggles, we discussed that mental hurdles and habits can get in the way of us reaching our fasting goals.  But it isn’t always mind over matter.  Sometimes we hit some physiological roadblocks.

In this blog post, we’ll discuss the three main reasons why we experience physical fasting side effects.

#1 Too little sodium



For most of our lives we’ve been taught to fear salt.  We’ve heard the warnings of extreme danger from our parents, doctors and the media.  Food manufacturers try to grab our attention in the grocery store aisles by labelling their products “Low in Sodium” in a big, bold graphic on the front of their packaging.

Historically, humans thrived while consuming 4000 to 6000 mg of salt every day.  Our current recommended daily intake is less than 2300 mg, which is a far cry from what we used to consume.  Salt is so critical to our well-being that we’ve gone to war over it.

But, if salt is so critical, why do we try so hard to restrict our intake of it in 2019?  In his ground-breaking book The Salt Fix,  Dr. James DiNicolantonio takes a look at how we got into this point and how salt is actually beneficial for maintaining normal blood pressure levels and preventing type 2 diabetes.

It turns out that not taking enough salt is actually detrimental for our health, not the other way around.  And this is the number one issue we see being the cause of almost all of the physical side effects of fasting from headaches to gout attacks.  In fact, we have observed salt intake to be almost critical to the weight loss efforts of women in particular.

While a healthy intake of a natural salt, like Himalayan salt or Celtic Sea salt, is good for most of us, you should always check with your doctor before making any dietary change.  People who have chronic kidney disease or certain cardiovascular conditions need to be mindful of their sodium intake.

Tips for getting more salt:

  • Be more generous with your salt intake on your eating days when you season your food, and always eat salt to taste
  • Try not to consume refined and processed carbs when you’re not fasting to prevent unwanted water gain because you will quickly lose that water when you resume fasting, which can result in a loss of sodium
  • Try drinking bone broth or sugar-free pickle juice a few times throughout your fasting days until your body adapts to your new lifestyle
  • If you don’t like broth, or can’t find sugar-free pickle juice, then try adding a pinch of salt in a glass of water or on your tongue
  • Drink a cup of broth, sugar-free pickle juice or salty water for every cup of tea or coffee you consume throughout the day

#2 Not enough fluid


We often mistake thirst for hunger.  So, instead of grabbing a glass of water or tea, we grab a cookie or a biscuit.  The food will provide us with some hydration and the feeling temporarily passes.  When we start fasting and cutting out snacks, we don’t replace the hydration we get from the food we consume to quench our thirst with water.

Chances are your cravings on your fasting days and between meals isn’t from food, it’s for fluid.  You may need to set a reminder on your phone to alert you to drink every couple of hours throughout the day.

One of the questions we’re asked the most is “how much water should I drink?”  Everyone wants a magical formula that factors in their total weight, height, age and gender that spews out an answer like 88.432 ounces of water a day.  Unfortunately, that’s not how it works.  I am 5’3” and my husband is 6’4”.  I drink roughly five times the volume of fluid he does.  There is no magical formula, and overhydration is just as dangerous as dehydration.

Drink when you’re thirsty and stop when you’re not.  That’s the bottom line.  Initially, you may want to try to drink a glass of water or tea if you aren’t sure whether you’re hungry of thirsty.  Overtime you won’t need to do that because you’ll be able to distinguish between the two.

Tips for making sure you drink enough:

  • If you think you’re hungry, try drinking a cup of water and waiting 30 minutes to see if the hunger passes or if you were just thirsty
  • Set an alarm on your smart phone or watch to alert you every couple of hours to have something to drink
  • Mineral or carbonated water is particularly good at alleviating hunger pangs

#3 Anstaining from activity 



One of the biggest myths about fasting is that you need to take it easy when you’re fasting, especially if you start to feel tired.  If you start to feel fatigued when you’re in the middle of your fast the surest way to feel that you’ll start to feel absolutely terrible is to rest.  Instead, you need to get up and get moving to get your body burning more fat to provide you with energy.


Burning body fat takes work and our bodies want to conserve as much energy as possible.  When your fuel stores start to run low, we’ll often start to experience feelings of lethargy and hunger.  This is our bodies trying to tell us fuel is low, and we need to eat because it wants to not spend metabolic energy burning body fat.  But if you continue to fast and slightly increase energy demands, then you’ll force your body to start burning body fat and refuelling your system.

You don’t have to go crazy and do a hefty weight training session.  Going for a leisurely walk, joining a yoga class or even cleaning out your closet are all forms of activity that can kick fat burning into gear.

Always listen to your body.  If you feel unwell, break your fast.  There will always be another day to fast.  If you feel like you can go do your regular weight training workout, then do it!  Personally, I have the best weightlifting sessions around 96 hours into my fast.  But, if you feel sluggish, then try to go for a walk or do some gardening.

Tips for moving on your fasting days:

  • Maintain all your regular activities on your fasting days as you do on your eating days
  • If you feel low energy, then scale back on the intensity of your activity but don’t stop moving altogether
  • We understand that some people are very nervous to start fasting especially if on medications, if that is the case then we encourage you to stay active at home doing gardening, chores and other projects around the house
  • If you start to feel sluggish during your fast, then get up and go for a walk for 15 or 20 minutes

Personally, I jump on a mini trampoline called a Rebounder when I don’t feel well during my fasts since a lot of my day involves sitting at a desk.  Every time I start to feel like I need a nap, I jump on the trampoline for 10 or 15 minutes.  It worked so well that I bought a second trampoline so I could have one at the clinic and home.

  • Megan Ramos, Program Director




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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