Fasting and Exercise: Safe or Dangerous Combination?

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

2019-01-24T10:32:56-04:0021 Comments

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Kathy Moran
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I am on my 4th day of a 5 day fast and I have been so protective of not doing much exercise-so afraid it would make me lightheaded! Thank you for the answer! My question is about blood sugar. I have T2 diabetes for 25+ years, have been on every bad meds and have been on solely insulin for 4 yrs. I started low carb, then keto, and now fasting since late November. Bent a little during but lost 8 lbs. Since then I have tried 24, 36, and 5 days(with my doctor). My medicines have been eliminated and now… Read more »

Jay
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Jay

Keep going! My suspicion is that your fasting is metabolising fat reserves, which are releasing stored sugars into your blood stream.

As for the exercise while fasting – I did an 18.5k run yesterday (11.5 miles) on day 3 of a fast and was absolutely fine.

Patti A Johnson
Guest

Fabulous info!! TYVM, Megan!!! 🙂 <3

Carol
Guest
Carol

Thank you Megan. Great article! I hear you (and other fasting experts) say that if you begin feeling unwell to stop fasting immediately. I would love to have a post or article addressing this specific issue. Why must you stop (other than….duh….you don’t feel good!)? I wanted to do a 5 day water fast a few years ago, and the morning of Day 3 I began feeling nauseated. I actually did vomit some yellow, bile-y liquid a couple of times and I did break the fast at that point because I felt so yucky. But I want to know what… Read more »

Audrey Ortiz
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Audrey Ortiz

I would like to know, too, in case it happens to me. I’m not over weight, 5’10”, 138lbs. I’m sure I have a lot of fatty cells especially at my abdomen. I want the added health benefits from a 5day fast.

Janet
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Janet

@Carol: it sounds like you were just dehydrated, and maybe low on salt. Vomiting yellow (or green) bile basically only means that your stomach was completely empty at the time. It’s fairly common with the stomach flu, or morning sickness, for example. Stopping the fast was the correct move– you shouldn’t feel nauseated or “yucky”, just intermittently hungry, during a fast. Better to take a break, get your body back on track, and then take another go at fasting later. Next time, drink LOTS of water, and try some bone broth too. I’ve also found that it helps to have… Read more »

Carol
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Carol

Thanks for that answer Janet. I appreciate some clarification on what it means when that happens. At the time, I felt like I had “failed” my intended 5 day fast, but looking back, I don’t feel that way any more, and I’m glad I stopped when I did. Working up to longer fasts is great advice. Again, thanks!

BERRY
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BERRY

For me, instead of antacids, I’ve done the ‘reverse” w/ very positive results. 1 Tbspn of ACV in a cup of water has solved my stomach issues + all acid reflux while fasting. (Usually I follow the 1st cup w/ a 2nd cup.)

Mary Crone
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Mary Crone

What about people with Adrenal issues and exercise during fasting?

Mary Crone
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Mary Crone

What about people with Adrenal issues and exercise while fasting.

lindajrudnick
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lindajrudnick

Hi Megan: I recently joined IDM because I am insulin resistant but not prediabetic or diabetic. I guess you could say I am on the diabetes train. I saw Dr. Fung on the Reelhouse production called Fasting. I decided last July to do a 7 day water fast and then repeated it in August and September. In October I did a 10 day fast adding bone broth and bulletproof coffee which I learned about in The Complete Guide for Fasting. I thought I heard on one of your blogs that you don’t recommend these extended fasts except where the health… Read more »

gjeanieg
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gjeanieg

I would like to hear more about the 4 day water fast, as well. We also watched the documentary called “The Real Skinny on Fat” and would like to use the 4 day fast to activate stem cells to heal my husband’s eyes. The eye specialist recommended a stem cell therapy for his condition, but it is outrageously expensive. If my husband can activate his own stem cells by fasting, then why not?? Would LOVE to hear from Dr. Fung or Megan on this. My husband and I (already LCHF, and used to 16/8) plan to start the water fast… Read more »

Kathy B
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Kathy B

I have a question. I have been fasting about 16 hours per day since September. Recently the last week I just want to eat often and anything. What is happening?
I was feeling great and now this.

Jem
Guest
Jem

Hi, This is a great article. Thanks very much. I’ve been hearing that for severely obese people, exercise during fasting is counterproductive because it stresses out the body and produces cortisol, which slows down weight loss. I know exercise is fine for people who trying to lose just a few pounds, but was not sure what the facts were for morbidly obese people. My other question is this. I know a ketogenic diet is close to fasting based on what Dr. Fung said in a lecture I watched. I want to know whether for his morbidly obese patients doing e.g.… Read more »

Tania
Guest

I would like to know this also. In addition, I have exercise induced asthma. What would be recommended in this case?

Eva
Guest
Eva

I actually found that HIIT training (High Intensity Interval training) has been really great while on a fast. I short, tough and very efficient, especially for boosting fat burning and even mores so in the middel of the fast. I do mostly Tabata which is 4 minutes extremely hight intensity training with 20 seconds full power and 10 seconds break. It should feel like the worst your minutes of your life and you should be completely out of breath when done. I change between exercises such as Burpees, star jumps, Mountain climbers, jumping squat, sometimes with dumbbells. I do this… Read more »

Carol Lavoie
Guest
Carol Lavoie

Prediabetic—I have been fasting for a few weeks for 5-7 hr of eating, a very low carb diet. (50-80 grams) I had a 24 hr bug in which I did not eat for 42 hrs. I was excited once I felt better to check my bs, it was 99.
I am worried because my bs have been 102-160. I’m going to have to be more active and check my bs before and after I eat. What can I do to help me reset my bs?
I refuse to be a diabetic but I need advice.

ilja
Guest
ilja

how do i not cave in and eat tons of carbs after 20hours? been trying fasting since last summer and gained 3 kilos (20/4 doesn’t work)

sorry for the question, don’t think i should pay 39$ a month for this one problem, unless it helps

BERRY
Guest
BERRY

The “kicker” IMO is that the first 2-3 days of fasting DO bring cravings & desires for food. (and 20 hrs is definitely in that time frame) — One idea would be to write down a plan of action or even a meal plan for what you will do following your fasting. Maybe writing it & talking to someone (friend/family) may help you hold tight to your goals. — With that said, what are your goals for fasting? Why do you fast? Are you eating nourishing foods when you are not fasting? — Sometimes getting perspective on why one does… Read more »

Ethan Joffe
Guest
Ethan Joffe

From my understanding, exercising while fasting likely has a big downside, which is that you do not have any external source of protein to use for anabolic muscular buildup and repair. As a result, it is likely you will have a catabolic breakdown from some other source in order to supply the needed protein, which is a bad thing, since there aren’t any “reserves” of protein in the body afaik.