How To Turn Yourself Into A Fat Burning Machine By Fasting For 24 Hours Then Going Out And Do Monster Workouts Without Bonking.

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Articles, Low Carb & Ketogenic Diet, Podcast

Click here for the full written transcript of this podcast episode.

A few weeks ago I tweeted about a fasting low carb diet:

I received multiple responses of “Yes!”.

The guy I mentioned in that tweet was Peter Attia, who has been on my show before in the episode “Is It Possible To Be Extremely Active and Eat A Low Carbohydrate Diet?”.

As promised, I got him on to talk about how to turn yourself into a fat burning machine by fasting for 24 hours and then going out and doing a monster workout (without bonking), and in today's interview with Peter, I ask him:

-Do you stay in ketogenesis all the time?

-When you do something like fast for 24 hours, then go on a long bike ride, what exactly are you trying to achieve?

-What do you actually take on or before a long ketogenic training session? Any calories at all, or just some kind of supplements?

-What do you think is the ideal protocol for someone during a workout in which they want to maintain as high an intensity as possible, but also burn fatty acids as a primary fuel?

-Do you think there could be potential side effects of this approach, such as a decreased metabolic rate, lower thyroid, immune system deficits, or anything like that?

A few resources Peter and I discuss in this interview are (and by the way, sorry about my ice crunching habit, my mic sensitivity was turned up way higher than I thought!):

-Abbott Diabetes Care ketone monitor – This is the device Peter uses for checking his glucose and beta-hydroxybutyrate (B-OHB) levels (those are his ketones).

-Medium chain triglyceride oil or coconut oil – either of these can be used before or during exercise to give yourself extra fatty acids to utilize.

-UCAN SuperStarcha corn based starch fueling product with very low release of insulin and extremely stable blood sugar compared to other gels, sports drinks, powders or bars.

Questions, comments or feedback about combining fasted workouts with low carbohydrate diets? Leave your thoughts below.

Ask Ben a Podcast Question

29 thoughts on “How To Turn Yourself Into A Fat Burning Machine By Fasting For 24 Hours Then Going Out And Do Monster Workouts Without Bonking.

  1. Eric says:

    I have come to find that my highest energy and best performing workouts are in the early morning following a 24 hour fast that lasted between Saturday and Sunday dinner. I can’t seem to find any science behind this though. Can you help explain at all? Thanks

    1. Combination of autophagy and better absorption from the fast most likely. Body is detoxed and digestion is improved having had some time without food intake.

  2. Lee says:

    Dude dude dude!!!!!! I had to turn this off halfway through because all I could focus on was you crunching ice lol

    Otherwise keep up the good work your information is awesome. Just maybe cut back on the ice crunching while talking ha ha

  3. Bree says:

    Is there a transcript of this anywhere?

  4. dlawiii23 says:

    Hate to ask again but could you upload the audio file again? It's not letting me stream or download.

    Can't get enough of you and Peter right now! Been eating high fat, moderate protein, low carb for three days now and my Ketone stix are bright purple which seems too soon. I bought a Precision Xtra and some test strips on Amazon today so we'll see what that shows.

    1. No worries! It is fixed. Enjoy!

  5. Pierre says:

    Hello folks,

    My main concern when being on a ketosis is that when performing endurance events it would be likely that our body burns fat instead of the ketones.
    Also when on ketosis is it possible to be in an anaerobic state?

    I understand we burn fat only in ketosis but it depends on the effort level right?

    1. Hey Pierre, you should listen to the podcasts I guest hosted for Jimmy Moore over at La Low Carb Podcast. We talked about all of this in great detail!…

  6. Tom P. says:

    Ok. Thanks for that insight. I never picked up on that fact.

  7. Tom P. says:

    During the interview Peter mentioned sodium and salty nuts. What is it about the salt/sodium that he finds necessary.

    1. Because your blood pressure drops on low carb from your body dumping carbs, water and sodium!

  8. Peter Attia says:

    My comment was really a statement about staying in ketosis. Single large servings of protein (or carbs, even 30 gm) can easily knock you out of ketosis.

  9. Rebecca says:

    Getting my ketones high enough while being pretty strict with carbs (under 20) and protein around 100 has been all over the place. My morning levels have been anywhere from 0.1-0.6- never over 1. That being said I do crossfit 3-4 times per week-do you think I need to back down on my exercise intensity. I have noticed my blood glucose is in the 90's sometimes in the evening after crossfit where it is usually in the 80s in the am

    Any advice would be great!

    1. That's likely the stress from the exercise driving glycogenolysis from liver and muscle stores to bump up blood sugar. I'd be checking your ketones, though, not your blood glucose. That way you'll know for sure…

      1. Rebecca says:

        Thanks I have checked them with the glucose and sometimes they are higher in the upper 1's and sometimes not so guessing best thing might be to decrease the intensity over the next few weeks and see what happens. Wish I could find a cheaper source of strips because I would love to test 2-3 times per day until I get it figured out!

  10. lowcarbironman says:

    Good podcast guys,

    I have a question – Peter, are you as strict on the idea of staying within 0.8-4 for ketosis (you call it binary, in or out) or do you think fluctuations in or out are ok? Mark Sisson did a podcast with Jimmy where he feels that you can be more flexible and ketones can vary depending on time of day/fasting state/nutritional intake, which disagreed a little with this idea as he said that you can still be in ketosis but burning them , hence the lower blood level.

    Where this is relevant is with someone like me (amateur iron-distance triathlete), who doesn't want to be restricted so much that I have to weigh every piece of food I eat to count the carbs, I can't ever eat out, and I like a lot of vegetables. Could I eat relatively more normally (~80-150g carbs per day, MDA style) during the week, then fast into a longer workout (eg long bike/run), where I will be in a higher state of ketosis due to the fast, and derive similar benefits. I would obviously build this up slowly as you discussed!!!

    I have some superstarch on the way (hard to get in australia!) and currently using 32GI (palatinose) which is similar in insulin-spike but with a lower molecular weight, do you think you should avoid this (superstarch) during exercise or can it be used during the workout without blunting the ketogenic benefit (I ask more from a race-fueling-rehearsal point of view)?


    1. Peter Attia says:

      Correct, you don't have to be in ketosis to burn fat. In fact, ketosis is "just" a state where your liver makes enough ketones to offset much of our brain's dependence on glucose. Hence a B-OHB level of 0.5 mM is quite different from a level of, say, 4.0 mM. In the former — sort of the threshold for entering ketosis — brain still requires most of its energy in the form of glucose. In the latter, the reverse it true.
      With my fasting experiments my level of B-OHB fluctuates greatly, and even dips "out of range," especially following a meal, since the meal contains so much protein.

      1. lowcarbironman says:

        Great! My longest run is 3 hours fasted, though the last 45mins were pretty awful! So will work at increasing it slowly! Thanks for your help :)

        1. mark says:

          hey try for superstarch in Australia

  11. Wanda says:

    Thanks for this interview, Ben. I started an experiment of my own this year experimenting with fasted workouts. I am up to about 2 hours now with my running on water only. I am also experimenting with intermittent fasting. I have found both enjoyable and am amazed I could hack my body this way. Hearing Peter Attia's take on this is refreshing and gives me added motivation to keep it going. Thanks again!

  12. Jojo2012 says:

    Great podcast! I've been experimenting with keto to lose fat without insane amounts of cardio. I've found it works great but I've wondered about being able to do lots of exercise on it. There seems to be a contradiction. Some say you need carbs fr lots of exercise. But if your body has abundant fat calories and can switch to that fuel source I don't see why it can't just do that. I recently did a long ride for me in a fasted keto state and felt no bonking but endless energy. I haven't been doing this for very long but I intend to see how long I can stay in this state and it's effects.

    I did have a huge bowl of pasta to see what would happen and I felt horrible for days, it may have been the wheat but it cured me of ever thinking I need to do that again.

    1. Geez, I can't tell you the last time I had pasta!

    2. Danny J Albers says:

      Jojo welcome to keto adaption and freedom from food. Sadly its a pasta free zone…

  13. Thomas Smith says:

    Funny, hearing you down breakfast/lunch, sounds like a smoothie? ;)

    1. Sorry about my ice crunching habit, my mic sensitivity was turned up way higher than I thought!

    2. Thomas Smith says:

      And Great stuff from Peter as always!

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