Bonk in fasted long run

  • Creator
  • #40579

    Hi !

    I do all of my aerobic training (+ sometimes more intense work) fasted in the morning without any problems. However, in my long runs I bonk after about 2.5h. I’ve tried a couple times to pass that 2.5h limit but, it seems that it is my ceiling

    Could you help me on how to deal with it and pull my fat adaptation over that 2.5h mark ?
    I’ve thought to reduce my carb intake for the non-long run days in order to train in a “more depleted state” when the duration of the workout is no more than 2h. What do you thing about it ?

    Thank you !

    Aerobic work: 8-10h/week
    Fasted = at least 10h after last meal
    Diet: high carb

Posted In: Nutrition

  • Participant
    Dada on #40583

    I think the high carb diet is the problem. I would switch to a more fat based diet. But I leave this question to others bc nutrition is not my home turf.

    Rachel on #40664

    have you thought about dialing back the intensity of your long run? It sounds like you are mainly carb burning if you bonk after 2.5 hours. I found last year the combo of fasted exercise & eating way more fat helped me. In fact I need to work on that again this year! You can really jump start by going high fat low carb but it’s kinda painful, at least it was for me (everything will be harder for a week or two).

    Rebecca Dent on #40666

    Hi Angelos,

    Thanks for your question. There are some good replies too. Firstly I would ask, how long have you been carrying out your fasted sessions for? Recently started earlier this year or longer? And as rachelp has mentioned you want to be carrying out your fasted sessions at a low intensity (zones 1 & 2) so perhaps think about what HR you are predominately working at during the longer fasted runs? With the uphill athletes I work with I tend to suggest a carbohydrate intake of 2g per kilogram of body weight per day and 3g-4g per kilogram of body weight per day on strength days/higher intensity aerobic workouts. Perhaps first start by going slower in your longer runs to be able to push past the 2.5hr mark and maybe just increase the time incrementally to 3hrs, then 3hrs 15min etc? Your suggestion of reducing carbohydrate intake on the day before your fasted run could also help so you are carrying out your fasted sessions in a muscle glycogen depleted state and not just following an over night fast when blood glucose levels are low. There are various ‘train low’ strategies that can help with enhancing fat adaptation. Perhaps start with reducing over all daily carbohydrate intake if you suggest you are a high carb eater (but fuelling high intensity/strength sessions with carbohydrate) and go slower in your longer runs. Let us know how you get on?

    Angelos on #40733

    Thank you all for your replies.
    I’ve experience with long and fasted efforts since about 5 years ago but it was about 6 months ago when I started doing more consistent and planned work (tftUA). Generally, I try to maintain my long run efforts in Z2 (ADS). However, in some steeper parts I might get some Z3 spikes, nothing special, 2-3 bpm higher than AeT, cumulating 20-30 mins in that low Z3. To be honest, I don’t really try to avoid it and probably, I should work on it (or/and retest my AeT).
    Talking about diet, I’m a university student and I can’t really afford a fat-based diet, I’ll try to have some low-carb dinners before my morning aerobic trainings and I’ll see how it goes.
    Thanks again for your suggestions !

    Anonymous on #40847

    …cumulating 20-30 mins in that low Z3. To be honest, I don’t really try to avoid it and probably…

    20-30′ of Z3 is a lot, especially if it’s repeated in multiple workouts. For that amount of Z3 per week, you should have about 7-10 hours of Z1/2 to support it. As others have said, it sounds like you’re going too fast too often.

    Talking about diet, I’m a university student and I can’t really afford a fat-based diet…

    I haven’t heard this before. What do you find expensive? I think a whole food diet limited in processed food is more expensive than processed carbohydrates, but that’s not because of the macronutrient content. If your diet is “high-carb” because it’s highly processed (pasta, bread, etc), it will be cheaper, but that will have even more downside than a high-carb whole food diet.

    (Rebecca, feel free to correct me if I’m wrong!)

    Angelos on #40863

    Thank you Scott for your comments !
    I’ll certainly be more conscious and strict on the intensity of my workouts from now on !

    By saying “high-carb” I don’t only mean highly processed. For sure, I do eat pasta, bread and other wheat-flour based products though in moderation. Whole foods such as legumes (beans, chickpeas), oats, rice and vegetables constitute the biggest part of my diet but these are high-carb as well, right ?
    I do eat fish, meat, nuts too. However, what I am saying is that I can’t afford those high-fat/low-carb options as the biggest part of my daily diet (at least here in Greece these foods are much more expensive than legumes and veggies) in order to significantly reduce the total carb intake and replace it by fats.

    Also, I should mention that very often I have to eat in the restaurant of the university (there are whole food options there but again mostly carbs) so it’s not always up to me to choose whatever I want to eat

    I appreciate your comments !

    Rebecca Dent on #41024

    Hi Angelos,

    How old are you? You don’t need to follow a ketogenic diet to become fat adapted, there are world class athletes who consume carbohydrate that are highly fat adapted. Research has also measured and demonstrated this. Continuing to build on and be consistent with your training will continue to support your endurance performance (and fat adaptation).

    If you are still young, I also wouldn’t encourage such restrictive eating practices especially when you are already doing several fasted sessions through the week.

    What are you training for? I would suggest that 2.5hrs is a good time to be able to carry out training fasted, what is the purpose of pushing it further? In the main event the goal is not to see how far you can go and not eat, the aim is to make you more fuel efficient for the main event (and eat during the main event). The training you are carrying out fasted at the moment is still going to be having an influence on fat adaptation and endurance performance, it comes back to consistency over time. Also be aware that fasted training increases the stress on the body e.g. on the immune system /increase muscle damage, increase fatigue, so I would caution against pushing the time you can carry out fasted and the negative impact this can have, it’s about striking a balance. You need to be able to put in good quality training for your other sessions (that also count towards your performance) and not increase day to day fatigue which may also impact your day to day energy levels and motivation to study.

    Living on a budget: Depending on your existing budget it can be more expensive to eat a ketogenic diet, as it’s based on protein and fats, which are generally more expensive to buy and you also want to ensure you are purchasing good quality protein sources not just the cheapest off the shelf. As Scott explains however it may not be more expensive than eating a good quality diet containing whole foods. However this again depends on your starting budget. Often cost savings can be achieved via planning and preparing meals in advance and not just visiting the super market on the hop and also knowing what to purchase and what alternatives you can eat to increase healthier food options. It sounds like you can make some good choices at your University Restaurant.

    If you want to jump on a phone call Angelos and talk this through and clear up any confusion then you can follow this link and book in with me and I can help give you some nutrition guidance.

    Phone Consult with High Performance Dietitian Rebecca Dent – $50/30min – PAY AFTER YOUR CALL

    Angelos on #41101

    Thanks a lot for your advice !

    I’m 22 years old and I’m training for long mountaineering days, I don’t have a specific goal planned. Since I know that I need to build my aerobic base I’m focusing on that.

    A quick update to my initial bonking issue: It appeared to be that it was a matter of intensity. I focused on not getting in Z3 at all and it worked well, I ran up to 3h without problems ! I can feel that I’m gradually recovering from ADS and I don’t need to get that much slow on steeper parts so, it’s more manageable to keep my heart rate low. It surprises me that I can run in low Z2 on uphills and Z1 on flats.

    Anonymous on #41122

    I focused on not getting in Z3 at all and it worked well.

    Yes, as soon as your are above your aerobic threshold (the top of Z3), it’s only a matter of time and fitness until you bonk. Above Z2, you’re digging into your glycogen stores to a higher degree. Glycogen stores are less abundant than fat stores.

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