Fasting and Exercise: Safe or Dangerous Combination?

By Jason Fung, MD

One of the questions I’m asked the most is if it is safe to fast and exercise at the same time.  The answer is YES!  ABSOLOUTELY!  One of the worst things you can do if you’re feeling well while fasting is sit on the couch like a big starchy lump of potatoes. Exercising can help prevent episodes of hypoglycemia and reduce your very small risk of having issues when refeeding after a fast.

Rule #1: Listen to Your Body

Use common sense to help guide you towards the level of intensity of your work out.  If you’re not feeling well, take the day off and get some rest.  If you’re just feeling a big sluggish, go for a walk or do a light yoga session.  If you feel completely fine, then hit the weights.  You may have the best weight training session of your life!  I often do while I’m fasting.  Even if I’m feeling a bit tired during my fast, I often have an incredible weight training session since there are benefits to exercising in a fasted state.

Benefits of Exercising While Fasting

  • It can give you an energy boost
  • Exercise can bump up your blood sugar levels a bit while in a fasted state if you’re feeling a little low
  • Improved mental clarity means you’re more focused during your workouts
  • Increased adrenaline while fasting helps you power through those extra couple of tough reps
  • The combination of fasting and exercise also yields acute oxidative stress, which benefits your muscle machinery
  • Help you manage stress and anxiety
  • Boost growth hormone production
  • Improve body composition
  • Raise testosterone levels

Rule #2: Hydrate

In order to have a good work out regardless of whether you’re in a fasted state or not is to be adequately hydrated.  When we’re fasting, we’re not getting any hydration from foods.  It is important to remember to properly hydrate before and after a work out.

If you drink water right before you work out, it won’t work.  That water doesn’t work its way from your cup to your muscles immediately.  It takes time from the water to get from your stomach and to your muscles.  You need to make sure you’re hydrating close to the time you plan on exercising, but not immediately before a work out.

Also, if you properly hydrate before and after and work out, you shouldn’t experience any post-exercise food cravings.  Those cravings usually come about because we’ve gotten dehydrated.

The Hydration Protocol

  1. Drink one of the following fluids 45 to 60 minutes before you plan on working out:
  • A glass of water with a pinch of natural salt (sea salt, Celtic salt and Himalayan salt to name a few)
  • 1/4 cup of pickle juice by itself or diluted in water
  • 1 cup of broth and salt to taste
  1. Repeat step (1) within 30 minutes of completing your workout.

The most important rule of all is to stop fasting if you feel unwell for any reason.  You can always eat wisely and get back on your fast when you’re feeling better.

Happy fasting and hydrating!

Megan Ramos, IDM 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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