Article with cautions on female fasted training

Posted In: Nutrition

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    Anonymous on #35671


    I’ll butt in here till Rebecca has a chance to respond.

    Here is our experience with fasted training. That experience is anecdotal but extensive with literally hundreds of cases both male and female. Rather than look for one black and white/good or bad answer understand that this is a highly nuanced discussion.

    1) Most importantly the author, David Roche comes to no conclusion concerning whether fasted training is on the whole good or bad. He does a nice job of presenting evidence both for and against fasted training. But, in the end there is no solid take away for this article.

    2) We ONLY recommend fasted training for low intensity session that are below one’s aerobic threshold. We do this because improving fat adaptation at these low intensities will raise many peoples aerobic threshold. By many I mean all but the well aerobically trained. As the article mentions; when one can use a higher percentage of fat at higher intensities that’s a good thing for endurance events. Numerous studies have shown that World class endurance athletes are highly fat adapted.

    3) We recommend that athletes train (in Z1-2) on fat but race (meaning any harder workout, race, climb) on carbs. The article correctly points out that lowered glycogen stores will negatively impact performance. So, if the event you are about to undertake will demand higher intensity or even moderate intensity for a few hours AND performance is important to you, by all means you should fuel on carbs, before and during the event.

    4) We have seen that the overwhelmingly majority (if I had to guess I’d say 90%) of the folks we interact with are terrible at utilizing fat for fuel. This indicates very poor mitochondrial function. Poor mitochondrial function means poor endurance performance at the very least and at worst serious health issues like type 2 diabetes and other mitochondrial disfunction diseases. So, improving fat adaptation is a good thing for health as well as performance.

    5) We see that people doing under about 8 hours of aerobic (Z1-1) work in a week can help jump start their fat adaptation with some fasted training in Z1-2. This speeds up some of the adaptations needed to move that 50/50 fat vs carb cross over point that David Roche correctly correlates with aerobic threshold in most people.

    6) At the higher end of the aerobic volume scale we see that athletes doing more than about 12-14 hours/week of aerobic work will be well fat adapted whether they do fasted training or not. I work with some elite endurance athletes who are vegetarian and eat a hagh carb diet but are training in the neighbor hood of 20 hours/week. They are all highly fat adapted and perform very well even in a fasted state. Those high volume trainers will be fat adapted because they will be in a nearly constant glycogen depleted state.

    As for the differences between men and women: I am not in a position to make any sort of broad brush pronouncement. However, I can tell you that Roxanne Vogel, who climbed Everest in 2 week door to door from her home in San Francisco, did a TON of fasted training and feels that contributed to her success. You can read about that here.

    In summary I would say that each athlete needs to evaluate what works for them. These points I’ve laid out above are just some of the factors that one needs to consider before making blanket statements.


    Rebecca Dent on #35693

    Hi Aaron,

    Thanks for bringing this article to our attention and thanks Scott for stepping in, it’s not controversial at all Aaron but great for discussion and conversation.

    I would totally agree with everything Scott has written. This article does not draw any firm conclusions and is perhaps more cautionary. I think what the article is really trying to highlight is ensuring that endurance athletes are eating enough to fuel their requirements as the issue of relative energy deficiency in sport has been brought to everyone’s attention recently. If fasted sessions are added in, this then further increases the risks of creating an undesirable energy deficit and insufficient fuelling.

    I think this has to be taken in a case by case context regardless of sex in terms of when to recommend fasted training (as Scott explains). What I have seen practically in ultra endurance athletes and uphill athlete clients is that regardless of fasted sessions it is about making sure with an increase in training load, dietary intake is matched to support fuelling, training adaptations, recovery and health. When fasted training sessions are added in they do further increase the stress on the body (i.e. immune system, increase in muscle damage, further rise in the stress hormone cortisol) so it is key that appropriate recovery is added in (in terms of training and diet) and the ‘athlete’ meets daily energy and nutrient demands, when this is achieved the risks are then minimal.

    I am yet to see any evidence on the detrimental impact of fasted training sessions and female athletes (when carried out safely and as advised with a supporting dietary intake that helps to meet energy demands), I think more research is being carried out on female athletes but I think the risks are there for men as well as in women.

    The other occurrence I am noticing more and more with athletes is that fasting days are being carried out in addition to fasted training sessions, and this I would advise against. Evidence has shown that when we spend extended periods of time in a negative energy state this over a period of time can start to have a negative impact on health and performance (such as those detriments the article highlights).

    My advice would be when carrying out fasted sessions appropriately it is really vital that you include a recovery meal/snack within 30-60mins of the fasted session (that includes carbohydrate and protein), to then ensure daily energy requirements are met via meals/snacks for the rest of that day to support recovery, training adaptations and health.

    It is also about good education around fasted training sessions and if the correct guidance is provided for athletes around fasting training then I think as Scott highlights, we know it is beneficial to endurance performance and health markers.

    Fasted training will have long term risks (in both men and women) if not followed appropriately and if insufficient dietary intake is not eaten over a period of time. Fasted training will also hold risks if that individual who is carrying out the fasted sessions is already compromised in terms of other confounding issues e.g. RED-S, an existing already low body fat/under weight, significant weight loss, over training, illness, or pre-existing history of disordered eating /eating disorders, menstrual dysfunction.


    Rachel on #35733

    I think Roche makes too many jumps in his logic in this article. First he makes the case for fasted runs. Then he jumps to this talk about a “low-energy state” and doesn’t define what it is. Almost all the negative implications for women arise out of this “low energy” state, where one’s hormones get out of whack, etc. He seems to equate fasted exercise with being in this low energy state. I don’t see any evidence for that. It almost seems like the opinion of a carb-burner who can’t fathom going for a run without fueling up beforehand.

    Then he claims women oxidize fat well naturally like we don’t need to try to improve it. And that fasting is bad for everyone’s mental health.

    There was one claim I found interesting: “For example, a 2010 study in the Journal of Science and Medicine in Sport found markers for muscle adaptations responded better in non-fasted female athletes, with male athletes responding more to fasting.”

    Aaron on #35760

    Thanks both on your thoughtful perspectives and candid responses. I truly did/do not want to generate controversy or wade into internet flaming. I appreciate this forum for the positive community and UA team support.

    pshyvers on #36309

    The linked article comes across as mainly warning about inadequate nutrition, e.g. poor diet, eating disorders, etc.

    Fasted training as I implement it simply entails running before breakfast in the morning. Although I am male, it’s been effective for me and I don’t really see anything in the linked article to make me concerned about it, male or female, as I eat right after. I keep it low intensity & the duration under an hour- I’ll start to crash if I go much beyond an hour.

    wildmoser.j on #37285

    It seems as though us females are overall at a higher risk of seeing adverse effects as results of fasted training and that maybe our hormones tend to, overall, have a higher risk of reacting negatively. Especially as far as cortisol is concerned.

    I cannot remember in full, but Dr. Stacy Sims in her book “ROAR” makes a strong case AGAINST fasted training for women. I read the book a year ago so it is not too fresh in my mind but it had to do with how it can easily lead to elevated cortisol levels (as in, too high for too long) in women which could even result in weight gain and belly fat (especially if you do not fuel enough). Basically, a negative effect on our hormones.

    She also states that women are overall more carbohydrate-dependent than men (+ that at different times in our cycle our carbohydrate needs increase/decrease. I cannot exactly remember when, though).

    Rachel I find the points you highlighted interesting:

    “Then he claims women oxidize fat well naturally like we don’t need to try to improve it. And that fasting is bad for everyone’s mental health.

    There was one claim I found interesting: “For example, a 2010 study in the Journal of Science and Medicine in Sport found markers for muscle adaptations responded better in non-fasted female athletes, with male athletes responding more to fasting.”

    This first point kinda runs opposite to the “women have higher carb needs” that Dr. Sims makes. But again I am only vaguely referencing her so don’t take 100% my word for it.

    This second quote/finding would only suggest that women are better off not doing strength training and/or anaerobic work in a fasted state, right? That said, I used to go to Crossfit at 6am for a while having only had a coffee and I never felt like I bonked… But eating lots of carbs (vegan here, haha) I am sure I always had sufficient glycogen stores from the night before to fuel an hour of Crossfit. I’m not doing it anymore though.

    Thank you for this thread because I am currently debating running in the morning before school. I have class at 8am so me running before means waking up around 5am and I really don’t wanna have to snack first, wait a bit and then run. I’d rather run on an empty stomach. I’ve done it a bit before and while I’d feel almost nauseous on a fasted run when I first started running, nowadays I can handle it really well… But all this “conflicting evidence” is making me unsure. I really don’t wanna get my hormones out of whack. On the other hand I just good my blood results back and thyroid function is totally normal so it would be a good time to start incorporating easy fasted runs… If something starts feeling off afterward I can just get my levels checked again and see if it had a negative impact…

    Steve House on #37409

    @wildmoser.j ROAR is a great book with some good information, but do keep in mind that she is not addressing endurance training. We (UA coaches) also advise against fasted training anytime you are doing high-intensity training or any kind of strength workout. It’s only for zone 1 and 2 aerobic capacity building workouts. Fasted training, as we define it (4-12 hours post meal) is pretty light-touch compared to a lot of what is being discussed as fasted training in the media these days. As with many solid, well-understood training modalities, fasted training is being (has been?) taken out of context and distorted to sell stuff.

    Also keep in mind that while being integrated into your zone 1 and 2 aerobic workouts we advise slowly increasing the time you go without eating, which means carrying a small snack or two. These times will improve over weeks, but it is never a linear progression. One week you’ll need to eat at 30 minutes, the next workout, 40 minutes, the next workout maybe 25 minutes. That’s all okay. It is our experience that most people can do their aerobic workouts and maintain health (health always takes precedence over training) within 4-6 weeks of applying these techniques.

    I do think your morning runs, (put a gel in a pocket) should be fine. Crossfit on only coffee, you could do it but you would have gotten more out of the workouts had you done them fueled. This is the reason we recommend against fasted strength training, carbs are the only fuel for this type of exercise and ignoring that means your muscles simply won’t work as well/fast/strong as they would with cho around.

    Lastly here is an article outlining a typical gradual introduction for fasted aerobic training.

    I hope this helps.

    Tips for Fasted Training

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