Fasted easy runs

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    Should I do all my easy runs less than 1 hour fasted? I signed up for level 2 Full IM plan. Thanks!


    I would definitely not recommend that. Running without proper fueling will definitely affect your performance.


    I run fasted as I do most my runs in the morning.

    If I am doing a long run 10 miles+ I would probably have a banana beforehand and bring a gel or 2.


    I also run fasted most days, apart from my long run


    you are asking “should I do all my easy runs fasted” – I guess the answer would be no.
    If you would ask “could I do all my easy runs fasted” – I guess the answer could be yes.

    There is a place for fasted runs or exercising. I think those are normally long runs rather than every easy run. Here a snipped from one of Matt’s Blog posts:

    “Fasting offers another way to enhance the training effect of long runs. When you withhold carbohydrate in particular before and during long runs, your muscles are forced to rely more on stored fat to supply the energy they need. When done with some regularity, so-called depletion runs increase the overall fat-burning ability of the muscles and thereby increase endurance. In addition, when you run long in a fasted state, your muscles reach a deeper level of glycogen depletion than they would in a normal long run. This triggers genetic adaptations that improve aerobic capacity.”

    I’m sure that either Matt or David can give much better answers.


    David Warden


    Your post generated an internal debate within our 80/20 coaching staff. We came to the consensus that we do not need to come to a consensus. Here is a sneak peak at our internal debate. The short answer is, “maybe, but probably not.”

    Leyla: I would be a no even if the session is less than an hour and easy, and particularly if they have another session that day. Do they need heavy carbs during a shorter easier session – no, but something small beforehand, light hydration during, and then a post-training snack and back to normal eating. Here is an article that I like on potential issues with fasted training for female athletes in particular, as it shows the conundrum with fasted training, that it does work for some, but when it doesn’t it’s not a great outcome – so is the potential performance gain if any for many athletes worth the risks?

    David: no for interval workouts, ok for easy or recovery workouts if you’re trying to lose weight. Not recommended for athletes who have met target body composition.

    Matt: I follow the science pretty closely on this topic. If you’re a moderately to highly fit athlete specializing in longer races and you’re doing all of the basic things right, sprinkling your training with a select number of designated depletion workouts will give your aerobic fitness a nice little boost. A few resources: It’s okay for us to have slightly different perspectives on this subject. My perspective is that nearly all of the risk comes from misusing and overusing fasted workouts, not from fasted training per se. And if a given athlete is not healthy enough physically or mentally to do fasted workouts without undue risk, then their health is the problem, not the method. As a practical matter, though, I prescribe fasted training sparingly because they are at best a waste of time for the vast majority of athletes, male and female, who aren’t doing some basic things right in their training and nutrition.



    Since I will face three depletion runs during my next training segment I took a deep dive into the subject. Everyone is right which is really cool…

    It is worthwhile to reframe the issue to recovery. I found the following review on “glycogen metabolism for coaches and athletes” informative and applicable to the training discussed here.


    I’m curious. If the goal of fasted training is to induce fat burning, why not just cut one’s carb consumption pre-workout or over the course of a week rather than cut calories completely right before the workout?

    I’m sincerely asking because I don’t know the answer. But it “seems” to me that you can still eat before a workout but focus on fats and some proteins rather than carbs. 100% fasted training has always struck me as questionable and risky.

    Thoughts from the experts?

    David Warden

    Mountainbiker, is this a conspiracy to cause a civil war within 80/20 Endurance? *Sigh* I’ll take this one back to the team, we’ll fight it out again, and then I’ll post here. 😉


    Matt Fitzgerald

    Increased fat burning is NOT the main intended benefit of fasted workouts. This is a huge misconception. The true main benefit is increased aerobic capacity. Depleting muscle glycogen stores during workouts stimulates physiological adaptations that increase VO2max. What you propose would not result in the degree of muscle glycogen depletion required to get the desired effect.

    A second reason why doing occasional fasted workouts against a backdrop high-carb eating is preferable is that a low-carb diet compromises training quality generally. By eating plenty of carbs most of the time you train better and get fitter. Then, by dropping in the occasional fasted workout, you get the complementary benefit of glycogen depletion, but in a surgical way that allows you to have the best of both worlds.

    Regarding risk, would a 10-minute fasted workout be risky for you? I doubt it. How about a 15-minute fasted workout? Probably not. Point being, fasted workouts are only risky if you take on too much too soon. I once did a 29-mile run completely fasted and I was totally fine, because I worked my way up to it. Also, the only real risk is fatigue. That’s it.

    3 Things That Work, But Not the Way Most Runners Think

    Think a Low Carb, High Fat Diet (LCHF) Might Help Your Running? Think Again!


    Sorry guys. I’m not trying to stir up trouble lol.

    Matt thanks for those links and what you say makes sense. However, I am also trying to reconcile it with another one of your blog posts which made the point that even if your 24 hour calorie amount is sufficient, but you go through too many intra-day calorie deficits during training windows, it can negatively impact your resting metabolism. I guess that is the risk that I am thinking about. Not trying to argue. Just trying to wrap my amateur brain around all of this information.

    Did You Get Enough to Eat?

    Matt Fitzgerald

    Two different things. Problems occur when athletes fall behind on meeting their energy needs every day, or close to it. What we’re talking about is a very limited use of a very focused method. For sure, step one is to take care of low-hanging fruit like eating enough throughout the day every day. But if you’ve checked that box, doing a fasted workout every other week or so can help you squeeze out a bit more of your potential.

    And for the record, you’re never “stirring up” trouble by questioning the guidance we at 80/20 Endurance offer athletes, as long as you’re doing so in good faith, which I know you are. I’m just a blunt communicator–the crusty old man kind of coach. So please, keep the questions coming. I’m not always right, so one of these days you may ask a question that causes me to change my mind about something.


    Thanks again Matt. I didn’t interpret your responses as being harsh. I was more responding to David’s joke about a conspiracy.

    Ok I agree with your point about using fasted training in a targeted and sparing way. I think I can live with and implement that. I just have two more questions:

    1. Would you still offer the same advice for a teenage girl? My daughter also runs and has been reading about fasted training. I got concerned reading the article in Leyla’s link above.

    2. What would be the downside of taking in calories from say (as an extreme example), a couple tablespoons of olive oil. That is effectively zero carbs so would, from a glycogen perspective, be the same as fasted training but your body is still getting some calories. I know two tablespoons of olive oil sounds nasty but then I know lots of people who drink pure baking soda before their workouts so…..

    And for the record, I am not a low carber. To me, it’s one of the most misguided diets out there but I am not opposed to using it in a targeted way sort of along of the lines of your view on fasted training.


    Hey Mountainbiker,
    Coming late to the party here. All of the points made above by Matt are valid and even in our chats we came to a conclusion that the “fasted training” itself is not the “problem” per se, it’s that often athletes add in these sessions when:
    1) they have not worked there way up to them appropriately,
    2) they have existing short fallings in their general diet for the amount of training they are doing
    3) don’t understand the purpose of the fastest training
    4) looking for a marginal gain -without focusing on nailing the basics first.

    You asked the question – about programming fasted runs for a teenage girl – and on that one I am personally still a NO. This is purely due to increasing evidence of the impact of Relative Energy Deficiency on young women’s hormonal health – the potential risks just do not outweigh the benefits in that case for me. Teaching young female (athletes in particular) to ensure they are eating enough for their level of training and developing a healthy relationship with the food they eat and with their bodies is essential for their long term physiological and psychological health.

    In regards to your second point… I’m not sure what to say, both of those ideas sound a bit wild… :0..olive oil or baking soda – ? I’m more of a half a banana kinda girl! 🙂

    Matt Fitzgerald

    I agree with Leyla. A lot of folks are attracted to fasted workouts for the wrong reasons. Adolescence is a delicate time, during which issues such as disordered eating and body dysmorphia are highly prevalent and can have lifelong negative consequences. There’s so much low-hanging fruit athletes can pull to further their development at that age. Fasted workouts can wait.

    To your second question, it’s not “cheating” to consume fat or protein before or during a depletion workout. There’s absolutely nothing to be gained from taking in these nutrients during one of these sessions, but eating a low- or zero-carb meal beforehand can at least mitigate the hunger factor. There is an amusing passage in my book RUNNING THE DREAM that touches on this matter.

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