Fasted training - why any limit on frequency?


Hey folks - when discussing fasted training, I’ve often heard to limit it to 1-2x per week, but I don’t quite understand the logic why. If you were doing endurance rides 4-5x per week (either in a polarized plan, or simply traditional base or offseason), why not do fasted rides as frequently as you can manage? Given the main training adaptations from these workouts, wouldn’t fasted training almost always add benefit to these workouts? Thanks for your thoughts (and any personal experience you have).

Some Help Understanding Fasted Training Recommendations

One of the problems with fasted rides is that your body just doesn’t have enough glycogen reserves to support a longer duration ride, or more intensity.

Fasted training does work well with lower intensity recovery rides, but if you are just doing recovery rides 4-5 times per week, well that isn’t a training program that is going to make you faster.

Also, even if you are pursuing increased utilization of fat as a specific physiological adaptation, it is worth remembering that using fat for energy requires oxygen, and therefore part of increasing fat utilization is increasing your AEROBIC capacity. And the normal training recommendations to do that are sustained zone 2 efforts, VO2Max work, etc. which definitely require sufficient glycogen reserves to do properly.

So doing 1-2 recovery rides per week in a fasted state may make sense, but after that, you are better off doing more demanding training with your body properly fueled.


Well in theory there should be enough glycogen stored in muscles and liver when working out in the morning to do something like a 60-75, maybe even 90 minutes Sweet Spot workout. This matches my personal experience. Only caveat: this will be lower if already depleted beforehand by light or low carb dinner.
So I disagree with only being able to do recovery L2 rides fasted.

As for OPs question regarding frequency: I would also be curious as to the reasoning to limit the amount of fasted rides per week. Maybe something to do with hormones/stress? Also I think RPE feels higher with fasted rides, so maybe more risk of burnout with lots of difficult fasted rides!?


@mcalista For a long endurance ride, let’s say 2.5 - 3 hours, depending on your level of fat adaptation / fuel efficiency you could very reasonably only be using ~25% carbs, which may add up to ~200 kCal / hr or so. I think even while fasted having ~500 - 600 kCal of glycogen available for a workout seems totally reasonable.

Definitely agree that recovery rides are fine fasted, and 4-5 recovery rides a week would equate to not much progress, but a plan with this much endurance / z2 work seems like it could easily be fueled by fat stores and endogenous glycogen vs having to take anything in before or during the ride.

Are you seeing endurance adaptations you would lose by doing the ride fasted? I hear you that maybe you could do longer duration with more added fuel - but if your time budget only allows 2.5 - 3 hours, and you can do that fasted, why not do it fasted?


@Bergfruehling I think the burnout risk you describe is real, and possibly some hormonal imbalances by putting your body in too much adrenal stress (if fasted rides do actually do this like some claim), but other than that this seems purely advantageous if I understand the benefits of fasted training reasonably well.

A few questions about fasting rides (fasted training)

If you were to train fasted all the time, you would probably see a large drop in the amount of onboard glycogen that you can carry, which depending on the type of event you race, would be a bad outcome.


@stevemz Any sense for why that is? I’m not doing low-carb, generally standard carbohydrate intake, high carb / pre-fueled before key workout sessions, but then fasted for endurance / recovery rides. Do you think the carb tolerance / capacity would still drop in this situation?


I’ll dig up the studies this evening.