Can you intermittent fast while training for cycling/endurance sports?

Say you had a heavy week training then are away on a weekend break, are you able to fast during the break away if you felt like it? Or would that trash your recovery too much? I’m thinking nothing too hardcore, just breakfast to breakfast maybe.

Also, calories technically break a fast, but how detrimental to the fasting process would it be if you had a coffee during the fast that wasn’t black - ie had milk or a little sugar in it. I saw something that said under 50 calories is fine. Sounds like a suspiciously round and convenient looking number to me.

Why would you do that for such short period? Are you afraid of gaining weight during your break?

I believe it would put your recovery in check. I would not fast but watch out for the calories and nutrients of what I eat instead.

Sure you can but it depends on how heavy the training week was and if you are used to fasting. During the off sesson I do 24h fasting once per week and normally train 10 hour weeks and that works well for me. On fasting days I just do easy endurance, typically 1h bike + 1h swim or 2 x 40 min runs. Closer to race season I go by feel and skip fasting on heavy weeks when I feel I need to and on race weeks.

Regarding milk or sugar in the coffee I would personally avoid it. Try with a teaspoon of coconut oil instead if you need something in the coffee. See

1 Like

I’m interested in how it feels when you’ve fasted for a while. I was away a couple weekends back and hadn’t eaten in ages and felt clear and sharp mentally. Like a lot of noise had been removed. I’m wondering if this is something particular to being on low carb or fasted or something similar.

Do you get anything like that out of fasting?

I listened to a podcast by Rhonda Patrick and it seemed that ANY calories would break your fast. The context was in relation to a specific biological process called autophagy.

1 Like

Yes but according to Mark Sisson there’s a difference if you’re adding fat e.g. coconut oil or butter:

Technically, it breaks the fast. You’re ingesting calories (depending on how much fat you add, it could be a significant number of calories), and calories break the fast. But pure fat has little to no effect on insulin, blood glucose, or any of the other measurements that indicate a “broken fast.”

He also mentions that it shouldn’t affect autophagy.

1 Like

Just based off my own experience with intermittent fasting I have doubts that you’d see any real benefits of IF over such a short period of time. I’ve only been cycling for about a year and felt like I needed to drop weight to make me faster on the bike. IF made sense to me because I’ve always worked out fasted anyway. It worked for me but as my fitness has increased I’m not sure that IF is best to continue because I feel like there’s only so much work you can do with no fuel in the tank.

1 Like

Honestly, fasting for over that short period of time (1-2 days) will do very little in terms of what IF does. Technically fasting in the way you are describing isn’t really even IF, it’s just a 24 hour fast.

I’m an experienced IF’er, mostly on a 17/7 cycle and do it pretty much all year, except peak summer riding/running and the holidays. I also eat lower carbs on days I am not on the bike or running and add in more carbs loading into big days on the bike. Overall I’m pretty loose with what I eat during my eating window but always choose whole natural foods, but the occasional treat does come in.

I also have done multiple 24-72 hour fasts (not IF). But those experiences are very different. Especially if you have never fasted for a significant period of time.

With a short fast, that you are describing, it will be hard. You’ll struggle with hunger and energy. However you probably will noticed improved mental focus and sleep. Whenever I’ve done fasting I always get both, even the first few times I’ve done it. Physically and training wise I can see almost no benefits, beyond maybe a reset for your system.

Read about and pay attention to what you break your fast with. I get massive digestive issues if I break my fast with pure fat. I’ve found bone broth to be the best, for fasting and IF, especially one with apple cider vinegar in it. I usually wait 30-60mins after bone broth before I have a meal.

But… If you are coming off a heavy week of training… I’f not fast at all. I’d focus on sleep, rest and proper nutrition. Eating clean and whole food will give you far more benefit into the next week of training.

1 Like

A short fast in some ways is not a great idea and you may feel like crap. Usually when I do it I start to feel like crap between 30-36 hours in. I get headaches, a lot of mucus and drained along with general muscle fatigue… After around 36 -40 hours everything seems to clear up and i feel great.

Breakfast to breakfast would be fine but I would suggest lunch to lunch. Your body really does not need anything to get going in the morning. It’s programmed to survive so everything kicks in.

if your having coffee then either add heavy cream to it or coconut oil or mct oil. Don’t add sugar it will just mess with you. Id you must add some stevia or erythritol or something like that.

Best of luck.

1 Like

Just out of personal experience, I felt really good incorporating (often can’t help it & just happens… you know, life!) couple fasted days during the week… not back to back. Provided that you continue to eat well throughout the rest of the week. Digestion gets a recovery day and ‘unpuffed’ after. And also some of my best sleeps!

I’m not so much a believer in lengthy fasts, mainly because I experienced digestive issues last year and want to keep the good/balanced gut bacteria I’ve got now, and not “starve” them. Had some slow weight loss as a result too, bonus! This is over months tho, and have an active hospitality job. I haven’t done this much at all this year, but haven’t gained those kilos back either.

At the end of the day, it’s a matter of trying it out. See how you feel days after. If tired, recognise and don’t dwell on it. Again, if your eating well and refuelling on the other days it’ll get you through the fasted rides. That’s if it works for you!

A coffee or a small bar isn’t an end all, be all of a fast. It might be just enough to keep you going about your day, or becoming useless at work haha. Heck, probably takes more calories to digest it haha.

1 Like

Oh. Yes you can intermittent fast while training. I rode 1000 miles doing IF over 8 days and ate less than 250 calories a day in 1 meal per day although I did not eat at least one day. I also fasted 3 days before I started the ride if I remember correctly.

I burnt about 25000 calories from riding not including my bmr and consumed about 2000 calories total on the trip. Some of my fasts were under 24 hours and some were over as I usually ate at a subway depending mainly on weather as I was dodging some rain and hail storms. One storm hit me so hard I ended up in the ditch because of the hail lol. My meal on the days I ate was a tuna salad from subway with the tuna and a lot of veggies with salt and pepper. No dressing or sauce on it. I may have had shredded cheddar on it but do not remember.

But this is not for everybody. I have one very skinny friend that If I dont remind him to take a gel or something every 45 minutes he will bonk to the point of being ill or pass out if we let it get to far out of hand.

Its all experimentation. I’m Fat. I think I could ride across the continent on electrolyte tablets, vitamins and water. I just need a sponsor to try it lol.


Same as others have said I had no issue with aerobic work and even anaerobic. However sweet spot and vo2 were brutal and eat on those days for sure now. But if fasted training followed by a cold shower helped me drop over 100 lbs in less than a year

1 Like

Way to go!!! That is incredible!

1 Like

I do this quite a bit. Not totally convinced of some of the purported benefits of IF, but find it an easy way to manage calorie intake on rest and easy days, generally feel sharper and better for it, and haven’t seen any downsides so that’s good enough for me. If there are additional benefits like increased fat burning then that’s a bonus.

As others have said, I wouldn’t do breakfast to breakfast though, the first few hours of the day are the easiest to get through. I normally end up on something like a 17/7, will have a prompt lunch at 12ish then a light meal at 7ish so I’m not going to bed hungry. Have incorporated IF into recovery days on fairly big training weeks (6-700TSS) with no problems as long as I’m taking on the right nutrition to fuel and recover from higher intensity sessions.

1 Like

i used to do a bit of IF and would regularly fast for 24 hours once a week or try and maintain an 16/8 fasting window.

One question i always had was that i have always been told to eat straight after a workout and regularly train in the morning so could not incorporate IF properly. How long do you guys wait to eat after working out and has there been any consequences to this?

1 Like

i’d first ask “what are the main goals of the fasting” for you…then decide if you can accomplish those without fasting.

I do have athletes that IF but you really need to dial it in so you don’t wreck recovery or hamper an upcoming workout


Bringing this topic up again because I’ve been on the journey for a while now. I do an 18/6 IF schedule, I often do my TR workouts in the early AM, fasted, then eat at lunch. Sure a lot of the studies on endurance athletes, fueling for recovery, etc are valuable. But this could also be aimed professional athletes, with a lot on the line, not professional amateurs who ride in the AM then go to their desk job. I fall in the latter category, sure I want to win local races, but at long as I fuel for the events then all is good. So in short, I don’t “replenish my glycogen stores” after workouts, and I do my workouts fasted, sure it doesn’t always feel great, but from a getting lean as possible perspective it’s awesome.

For a stage race or a series of A races I will fuel regularly, no IF. I should also add that on weekends I change my IF timetable, starting Saturday AM I eat from 6AM - 2PM to fuel for the longer and harder outdoor bunch rides or “C/B” races. Then on Sunday, after 2PM, I fast all the way until Monday at 12PM. It’s been a great program thus far, and will only change if I cannot lose another kg (getting close to that already) and/or my performance falls due to bonking/fueling.