How long until "fasted"?

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  • #7142

    –Question: How much time since last calories-in qualifies as being in a fasted state prior to a workout?

    –Or–How long to wait after lunch before I’m officially “fasted” for an evening workout?
    If breakfast 7am-ish, then lunch at noon to 1pm, then nothing but water after that (no giving in to the 4 o’clock breakroom munchies!), how late would one need to workout that evening to consider being in a fasted state? Is 5 hours long enough (6pm workout)? 7 hours (8pm workout)? Longer? Workout would be followed by a late dinner.

    (Or is it enough to be 2 hours since last food to call that fasted, as recommended, for example, in the articles on DIY threshold testing?)

    –Not in the morning, please! 🙂
    The easiest solution is probably “Workout in the morning after not eating past 8pm,” but that doesn’t work for me when I’ve tried it in the past; I can’t seem to stick to it. I find my body is not very ready for training in the morning, although perhaps it is my mind. I feel stiff, not firing well, and prone to hurting something. (Plus the issues of needing to help get the kids up, make sure they are ready for school, and get them out the door.)

    –Relatively easy goals (but proving difficult for me):
    I have trouble getting enough sleep, so there are larger structural issues re: my discipline, my career and commitment to training, body rhythms, and daily schedule. I’m working on these to be ready for my backpacking and climbing goals next summer after not being satisfied with my fitness on this summer’s trips (and I’m only talking about 13K-14K peaks in the Sierra and RMNP by class 2/3 routes!). I’m about to turn 50 years old and don’t seem to have the energy and drive I used to, so I find I have to be more careful about how I do things these days, which should be no surprise.

    –Thank you for any advice, your previous posts, the book, and all the resources here, including the community! I have learned much already (and apologies if I have missed the answer elsewhere in the forum).


Posted In: Nutrition

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    lionfish90 on #7151

    OK, this UA article says about 12 hours:

    Train to Burn Fat

    “When you awake in the morning you will have presumably not eaten for about 12 hours. Your glycogen stores will already be somewhat depleted, even if you did not engage in a heavy training session the day before (more so if you did). Glycogen depletion has been shown in numerous studies to be one of the most powerful aerobic adaptation stimuli by signaling an increase in aerobic enzyme activity. So starting a workout in a semi depleted state kick starts the fat-as-fuel-adaptation process….”

    So I guess I will just need to experiment with 6-8 hours (i.e., lunch, evening workout, late dinner) and see how it goes and how I respond.

    Thanks for any feedback on whether shorter times than 12 hours still carry some of the benefits!

    Anonymous on #7154


    Talking with Rebecca from UA, she did say that technically my 1h30m Z1/2 workouts I do after work offer some fasted benefit. I eat around 1100 and workout around 1500-1600. On Saturdays I do my morning runs that are the 3h Z1/2 efforts. Those are completely fasted. Since you have to get kids ready for school and all that, I would suggest adopting a similar schedule. For alpine objectives you have to start early… might as well get used to it where it’s safe before heading up some sketchy scramble in the dark!


    Anonymous on #7160


    You can only do what you can do. If mornings don’t work then I suggest trying to do some of your longer weekend workouts fasted or without eating during them. If you are not well fat adapted then you will burn through your glycogen reserves within the first 2 hours of these bigger days anyway which will then have the effect as if starting fasted. See how you handle 3 hour runs or hikes without eating during. This will have a powerful fat adaptation effect.

    As for exactly how long you need to go to be “fasted” I do not think there is a rule that will work for anyone. A well fat adapted person may still have pretty good glycogen stores in the morning after 12 hours. Whereas a poorly fat adapted person will typically see big swings in glycogen stores over the course of a couple of hours. This means blood glucose levels swing a bunch as a result and so does mood and hunger cravings resulting in this person’s feeling that they ‘need’ to eat frequently.


    lionfish90 on #7163

    Thank you Adam and Scott. Those are enlightening comments. Especially in the summer, I do my long weekend “LSD”, which are mostly bike rides, in the mornings to avoid the Texas heat; now I think of these as Z1-2/AeT/nose-breathing instead of LSD. But I usually eat first (and during) and will try not eating. My experience with that is that I bonk!

    My question is:
    Are you saying that in order to avoid bonking (i.e., draining the glycogen stores, I assume), it is better to train through or up to that point to train fat-burning? And that that is a way to increase volume, that when adding time to the Z1 workouts, one metric is to add time as capability to do so without fuel and without bonking goes up?

    I’m already doing most of my aerobic work at a heart rate of 135 bpm as top of my Zone 1 (TftNA scale), and this correlates pretty well with my “deep but not too urgent nose-breathing” pace. (My MAF is 131 bpm, but I use 135.) My “urgent nose-breathing”, where I’m actively/more consciously not mouth-breathing, is pretty close to my TftNA Zone 2 top end of 144 bpm.

    Uh oh, I suspect I am not much of a fat-burner (no surprise there from what I’ve learned lately from the book and the UA site…). I usually do longer rides, basically anything 2 hrs+, with sugar (Gatorade in the bottles plus a granola bar at about 1.5-2 hrs in) because I have bonked from mildly to quite hard right at about 2 hrs, typically in the heat.

    It was a long 12 miles remaining into a headwind on that hard bonk, too! Not fun, and I didn’t realize I should aim to train that away; I instead starting fueling with carbs during the ride and no more bonking (just tired and slow with a rising heart rate because my fitness and consistency have not been that great).

    I also do a lot better when hiking in to Sierra peaks with a pack (25 to 40 lbs depending on ropes/gear or not) when I have M&Ms and gummy bears or whatever at rest breaks. Well, what you say explains that!

    There is that story in the book of trying to do a long traverse/link-up solely fueled with peanut M&Ms, which I was surprised didn’t work. I’ve also seen the stories of Kilian Jornet (way out on the far end of the curve, for sure; he’s earned that) hardly eating anything on his long, fast (!) treks, such as taking only “4 Snickers bars” on that 7 summits all-day traverse in Norway by foot and ski. Those sound like opposite ends of the fat vs carb as fuel spectrum that you are talking about.

    Slaying the carb-craving dragon is tough, tough work! The one time I’ve done it for real, deep into my CrossFit phase over a decade ago now, it took about 10-12 weeks of constant Zone-diet vigilance to drive it away. I was the leanest and strongest of my life (which is not saying much). It only takes a couple of weeks of falling off the wagon into a sea of delicious sugar for it to come roaring back!

    OK, sounds like I have a lot of work to do here. Thank you for your insights, input, and time, which is much appreciated.

    Anonymous on #7184


    I think you should dial back the time and intensity until you aren’t bonking, then gradually increase from there. I would also suggest bringing something like a gu gel or shot blocks just in case you bonk. Be sure when you say bonk though, you mean actually bonking, complete with complete exhaustion, confusion, trouble with balance, etc, before you grab a snack. I’ve heard of people bonking before and they just meant they got really tired or their legs started getting fatigued, or they were dehydrated which is a serious issue. And remember training is different, so if you are on a goal climb or trek then definitely fuel the effort.


    lionfish90 on #7185

    Those are excellent points. Yes, in that case, bonking is not the right term. It was definitely going from “doing OK, if getting hot and tired” to “holy cow, I have to stop and sit on the side of the road” in a short time period (maybe 15 minutes?). I would stop to rest and not push into the “weaving around on the road” stage, which I could feel was on the horizon. And these episodes stopped with carbohydrate fueling.

    Dehydration is also a likely culprit, good idea. This is generally in the summer in south central Texas, where it will get to the high-80s by 9am or 10am (with dawn already around 80degF, give or take). I lose a few pounds on these rides, which must be due to water loss, but I don’t think I increased my intake of fluid, just switched from water to Gatorade (first in one bottle, then in both, and feeling better with it in both) to fix this. (Not the “tired and slow” from fatigue part but the “have to stop” part.)

    If fatigue, I suppose it just was that I was (and am, unfortunately) not in very good shape, meaning that my spotty training consistency (too much breaking from plan) was not able to support my weekend-warrior 3+ hour rides in the heat, even though I was monitoring intensity by heart rate. What I am trying to do this fall/winter is that I have re-started a Transition period and am being more consistent. My “long” Z1 efforts aren’t that long yet, so maybe when they get there, I will be prepared and will realize I was doing the “weekend warrior/taking too long to recover/train some but not effectively/repeat” that the book and this site describe.

    You know, that sounds pretty likely. Consistency is key but is surprisingly hard. I think I must have been sabotaging my aim to get fitter. So sticking to my Transition plan will be equivalent to dialing back the time and intensity for individual efforts that you suggest; my training time has increased, but it is spread over more efforts during the week (more day to day consistency in training, which has been my bugbear).

    Thank you for helping me talk through this. Apologies for the length and if this stuff should be obvious (“be consistent, duh”), but I think this is really helping me understand some things. Now I just need to test it over the next several months by sticking to the plan!


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