Fasted Workouts

So, I understand the importance of fuelling properly for HIIT workouts, but I’ve also heard there may be some benefits for being fasted when doing low intensity sessions (though happy to hear any opposing views).

Any ideas which workouts may be ok to do fasted? E.g. Recovery Spin, Open, Base+? Any others?

What about recovery weeks? Can these be done fasted, better to be fuelled or depends on the workout?

For arguments sake, we can assume accurate/updated 4dp profile and workouts at 100% (so we don’t get bogged down with discussions that any workout can be low intensity if you change the intensity to be low enough - unless you have actual settings to hand for each workout :+1:).


Hey Philip:

thanks for posting, very interesting topic and I’m interested to see what other say.

I have just been reading “Food for Fitness” by Chris Carmichael, and what I’ve been able to conclude is that he thinks any sort of fasted workout is not beneficial. He mentions that liver glycogen depletes overnight and since the brain feeds on this, it must be replenished before exercise in order to be able to perform well in the workout. I keep wondering, as you mention, if this would be bad for low-intensity workouts as well.

He mentions that even for short workouts you should have some food beforehand.

I, too, have usually done all short workouts fasted, so reading this has raised questions.

Looking forward to hear what others think.


Nice post. I am watching this topic.

I am working on a shift schedule and exercise in a fasted state almost every second week. The only time I fuel up beforehand is when the workout seems particularly intense or longer than one hour.


I try to make sure I’m fuelled for all high intensity/interval workouts so I give myself every chance to hit my numbers. If I do a faster workout I look for a zone 2 workout (endurance+ or modified workouts on the training plan) and do it on waking, may be taking on a little protein at 1 hour in, if it’s a long workout. I feel really tired all day after fasted workouts so have to pick them carefully.


If I suffer before work I’m almost always fasted state, mainly because I don’t want to get up earlier than I have to, but also hate relying on gels etc, and I (usually) seem to handle them pretty well up to an hour.

I have on occasion started a workout and just knew pretty quickly I needed to fuel. I do keep some gels nearby, so will get something in, but for a short 1-hour workout, I wonder if at that point it’s too late anyway.


Hi Philip.

Assuming you are just doing it for fitness and to get faster, then you will get by most short (45mins or less) sessions without fuel. Make sure you refuel as soon as possible afterwards though.
For me, I am always fasted as I can only do training first thing in the morning. However, I have at least one bottle of home made sports drink to have during the session (salt, potassium carbonate, maltodextrin, etc.) . If it was a longer session I may eat a few dates before getting on the trainer.



I used to only ride fasted. I wasn’t in SUF at the time - was recovering from a bad knee smash and had just discovered indoor stuff as a recuperation thing.

my experience is that fasted is fine for anything in up to an hour. And then if I was going int o something hard I’d then use a single gel maybe.

During that time when I was doing that - once I was back to normal’ish - I found that I did really well fasted and only occasionally I’d use something like a gel after half an hour of there was a 20-30 minute super hard second half coming up.
Lost weight as well.

These days I have to say I’ve got myself in to gels all the time now, whether morning or evening and so on. Outside too.

I think probably too reliant on them and while I have no side effects from using them I doubt it’s a great long term fuelling strategy.


Thanks for the replies, good to see some fellow Sufferlandrians also interested in this topic.

All my sessions are also in the early morning due to life. I usually take a gel before and a carb drink during. For outdoor rides, it would be a combination of gels, carb drinks and cereal bars. I would also have a recovery drink when I’m done as well. However, for recovery rides I’ve recently been doing those fasted and just eating normally.

From what I’ve read, HIIT sessions, no matter the duration, should be done fuelled to get the most training benefit. However, Z1/Z2 rides could be beneficial to do fasted in order to aid fat adaption. This means that something like Joyride should be done fuelled, whereas Endurance+ could be done fasted, even though it’s a much longer session.

In terms of my goals, I guess from a 4DP perspective it would be improving my MAP and FTP (essentially improving my speed and endurance), but also making sure I’m able to use whatever fuel efficiently.


Also interested. I also do my M-F workouts early morning and fasted too. Its usually not an issue if under an hour and I refuel right after. Weekends I always eat first and if there is something like The Shovel or Violator on the plan, then it’s wait for two hours or I’ll need the SUF bucket.

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I’ve done fasted in the past and lots of unhealthy things around being fasted and trying to lose weight. I can’t hit any targets above Z3 if I keep doing fasted workouts. I need those carbs to hit high intensity work outs. I’ve also gone too far down the fasted workout scenario where it is not good for you. If you start smelling like ammonia or your breath smells like ammonia, your body is eating muscle for fuel and that’s when you start getting weaker. For me, fasted is only good when I have good reserves built up in my body that can be used for the workout.


I was thinking of starting a similar thread so this is timely. I’m similar to many above, 4:40am starts so always and only fasted (except when doing 4DP, because I’m an idiot). The 30s pain shakes in blender nearly killed me the other day. The comments above confirm my status as an idiot.


I find training while fasted for longer endurance sessions in the off-season (indoor or outdoor) helps keep me going in longer endurance rides in season. For the shorter rides of less than an hour it doesn’t really seem to make a difference whether fasted or not. I do try to do a gel 15mins before Full Frontal and another gel just before the brutal 20mins start. Anything I can do to feel better about doing Full Frontal.


I learnt all about fasting 3 years ago when starting a low carb diet to lose weight. I lost 3 stone in approx 9 months, in the second period of that I started cycling and learned very fast that riding fasted burns fat and a good steady rate. Since I lost all the weight until present day on low but not super low carb way of eating and doing at least one longer ride and one HIIT ride a week fasted keeps the weight off nicely. Opinion will always be divided but I have proved that for me (and all our bodies and lifestyle are different) fasted just plain and simple works.
Size small Jersey for me please


Here are a couple of studies and critiques by the author of the site:


I trained follow the “Sleep Low/Train Low” approach a couple of months (
HIT in the evening, and no carbs during or after the workout. Then, a LIT session in the morning in a fasted state.

I didn’t do it for weight loss but body composition goals and performance gains. It produced some results, but it was very hard to follow (mostly the carb-depleted evenings).

My performance on the LIT sessions did not suffer (but why should it, it was around 90 minutes and going really easy), and eating all my carbs before the HIT session in the evening made sure I was well-fuelled for that workout as well.


I actually talked about fasted riding recently on the TrainingEdge podcast. If you have some time jump to the 45min mark and give our discussion a listen.


Thanks for the links. Will definitely read through them and listen to the podcast. Good to see the coaches pouring their thoughts on this topic!

@lifeintheslow - this sounds similar to what I was looking at in terms of carbing up for HIT and fasted for LIT. Though it’s interesting you didn’t take carbs after the HIT as I thought carbs were important for muscle recovery/building after a hard session. Though I understand this is so you are more fasted for the morning LIT session.

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Exactly. The purpose of the HIT session in the evening (additionally to the training benefit itself) is to deplete your glycogen stores as much as possible. Eating fat and protein after the workout should protect your muscles and other tissues, but without carbs, your glycogen stores stay low. The next day, your body is rested, but glycogen is not replenished.

I don’t know if this strategy is sustainable (or would lead to loss of lean muscle mass in the long run regardless of consuming protein), but in the short term, I didn’t see any negative side effects.


Listened to it today. The adaptation steps make sense to me.


In this thread there seems to be a mixture of results from scientific studies and personal experiences. I will not question the research results if the studies have been conducted in a reasonable manner.
On the other hand training is a very individual thing affected by tons of circumstances and variables one single study could never account for. So for yourself there will never be a better thing than experience. Just keep in mind your own experience may not be applicable for any other individuum.
That said I cannot report of any shortcommings in doing all the hard SUF sessions in a fasted state as long as they don’t last much longer than 1 hour (besides FF - I approach it always well rested and well feeded). Actually I nearly always jump on the trainer right after getting out of bed. That is because I never know if I can fit a training session in the late afternoon and don’t like to be worried about that the whole day. I never had any issues with doing both high intensity (AC, MAP) or more FTP oriented workouts in that fasted state. In fact I made very good progression with the SUF training plans.
That said I need to add, that I tend to eat relatively late in the evening so it may very well be my glycogen stores are well filled in the morning. Summing up I would suggest to rely on the SUF training plans and when it comes to diet and fueling just try out what suits you best. That’s strictly my personal point of view. But to get started with WHAT to try out it will almost never be wrong to stick to science.