Fasted(but not glycogen depleted) morning commute, how soon to replenish for afternoon ride?

So I have a 1+ hour commute and I’ve been using IF to lose weight and getting fat adaption over the last year+. I got to the point of 4 hour rides without any food and regularly do SST or Z2 for the morning ride, followed by either Z2 in the afternoon or a hard interval session. Haven’t been able to find an answer for timing after if someone is doing two a days. Closest is this thread Continuing fast post fasted ride

Generally I try to get a 16+hour fast in so even though I get to work around 10am, I try to push back lunch until noon-1pm. I usually leave around 5-6pm so I think there is enough time to reload glycogen stores but I’m wondering if I should eat my lunch earlier and/or have a snack/recovery drink right away and cut my fast short by 2-3 hours. I know that the morning ride is generally not glycogen depleted to start and likely won’t completely deplete my stores after but I’m wondering if extending the fast in a low glycogen state will improve fat adaption gains, and how do I balance that with replenishing for the afternoon ride that is higher intensity.

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the science now says though that fasting only creates weight loss due to caloric restriction, not necessarily more fat burning. Have you considered eating high carb and low carb based on the rigors of your cycling the next day?

Good job on the fasting! First of all I would avoid high carbs like someone just mentioned, this will spike your insulin and effect your fat adaption / autophagy. It sounds like it’s already working quite well for you, so as long as you’re doing at least 16 hours then keep it going. There’s no harm in going 18-20 hours and then maybe having an electrolyte right before your commute home.

Edit: I think the above comment might have meant to say high fat / low carb, which I highly recommend. It’s worked very well for me and there’s a ton of evidence based research out there on this subject now.

No I think he means to periodize high carbs prior to interval sessions. I know I can’t go 18-20, ie no food before the afternoon ride if its going to involve any intensity or I’ll bonk hard. If no glycogen replenishment occurs between the rides I can’t reload enough through gluconeogenesis even being more fat adapted

The weight loss is due to calorie restriction(CICO) yes, but the increased fat utilization on the bike is an added side benefit that I know is coming from the IF. I’ve been cycling for ~10 years and could never go over 3 hours without food prior to starting the IF.

I’d agree with periodizing carbs. Would you agree with the carb intake schedule in this post?


Been doing regular 36 hr fasts and lower intensity rides on those days (not eating until the following day). At the end of some of those rides I do sense the body is getting low on reserves. If the following day has a high intensity workout it seems to take the whole day to replenish store enough to take on Vo2 max intervals. So it really depends on how far you run down the stores.


I think it’s pretty extraordinary how adaptable the body is though. A few years ago I would have considered 12 hours a good fast, but now after being fat adapted I’m able to comfortably go 18-22 hours every day with one 36 hour fast a week. Something that has helped me get through workouts is some added sodium and I’ll maybe have two black coffee’s throughout the day.

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yea the extended fasts aren’t really an issue, during the winter when I was riding a lot less I could extend them out, but last year I dug myself into a hole, trying to lose weight while building with the 2X/day sessions with IF. So trying to find the right balance this year

Only N=1

As I progress though ssb2 and build I sense the need to cut back on the IF and/or time it very carefully

I can’t fully refuel quickly for a VO2 max workout after completely emptying the tank. It seems to take over a day of normal eating to tackle that sort of workout effectively. Or very late the same day at a real push.

If you do any sort of fast on the same day - you are just killing the effectiveness and reducing the benefit of the high intensity workout.

That’s been my experience too if I completely empty the tank, but generally I don’t think that is the case. I usually burn between 450-650 calories on the commute in the morning as measured by a PM. Mostly I try to limit the effort to sub Z3 if not Z2 so 30-50% of the calories come from fat. What I’m really trying to figure out going into this summer is if the additional gains from the increased fasting after partial depletion are more benefical than the additional time to reload glycogen stores that weren’t that empty

Trying to do both fast and any intensive exercise in close proximity seems counterproductive. It takes a fair while to refuel. So it all depends on how much of the tank you empty. Extending the (partial) fast after a ride will just lower the glycogen stores further making it more difficult to refuel quickly. AFAIU you are not doing it long enough for any significant long term fat adaption so it only serves to mess up the refuelling for any higher intensity workout. So personally I’d not do any fasting on a x2 day unless they were both low intensity and then I wouldn’t bother with any significant carb refuelling anyway.

It seems there are lots of ways to approach fat burning

  1. Lower the glycogen stores for an extended time, low carb consumption ie. fat adapt your body
  2. Do lower intensity work and burn it as a % of the fat/glycogen mix - with or without fasting
  3. Do HIIT boost your metabolism and potential fat burning
  4. IF and ensure ride intensity matches the IF regime to maximise fat burning after glycogen depletion
  5. General Calorie restriction

Fat adaption really does seem to be a different thing all together - teaching the body to run on a different fuel and takes weeks of continuous low glycogen. And (AFAICS) it is just for real endurance devotees.

I could be wrong - but I feel you only become partially fat adapted on IF, i.e. you become less dependent on carbs and possibly make more of the carb boost when ingested and it may be the case that you burn a greater % of fat than you would without IF.

I’ve tried to be more fat adapted - I lost weight, got used to running on mainly protein and fat (improved endurance fuelling) - but just couldn’t do the intensive stuff on the trainer or outside. Hills of any significant kind were truly horrible and higher intensity workouts just made me want to stop cycling altogether.

Conversely with IF I get the weight control, ability to still do a range of exercise intensities - but no great sense that you can ride any further without regular carb fuelling. 50 miles is the longest morning ride I’ve done on a cup of black coffee and I don’t need to go any further that often - so why go through the torture of a low carb regime with all its limitations. If I was doing regular centuries or a significantly long distance ride it might be a different preparation story.


But why would you go 3 hours without food? What the point of that restriction?

Plenty of people have reported fat adaption without exercise using a 16:8 IF regime and my N=1 from last year would agree with that. Its not necessarily for any performance benefit but I like the nutritional flexibility for long rides so I don’t have to pack as much food and/or make stops. I can ride a century on 1 bottle of mix, a gel and a clifbar which before would require 2-3x the food. I do agree I’m playing with fire a bit with the 2x days and potentially limiting the quality of intervals. I stop the fasting in sept generally when CX season starts because my races are in the morning and I want to be fueled for those.

I’m not on the low carb train either, I’m trying to figure out the nutritional periodization to try to balance both similar to the ideas from

Because the literature shows generally a minimum of 16 hours of fasting is required for the adaptions to begin

So you weren’t taking about a three hour bike ride? That makes more sense. Doing a three hour bike ride without food not so much.

Sorry I think I/we may be mixing up points. I do 1-1.5 hour rides fasted 4/5 times per week, then I continue the fast for 3 hours off the bike. Thats the part I’m asking about.

Through this fasted riding I was able to work up to being able to do fasted rides for 3+ hours. The idea being that going into the ride fasted jumpstarts the glycogen depletion that is one of the main purposes of long slow distance rides do that you can get some of the benefits of 5+ hour rides during base training from shorter 2-3 hour rides if you do them fasted instead. The major adaption I’m after is being more fat adapted so a larger proportion of my energy is coming from fat at lower intensities. This helps with nutritional flexibility on the bike and being able to carry less food, and also helps with weight management on and off the bike having a larger contribution from fat even while sitting at my desk. Seems to help with cravings etc, i hardly ever get ravenous anymore whereas before I started IF I’d constantly be hungry throughout the day with my long 2 way commute+ other rides.

Last summer I did a week of IF where I was riding 6-11 hours a day. I had fasted for 3 days before I started the first day when I rode 11 hours without eating and then that night had an apple and 3 pieces of cheese. Next day I got caught in a storm at night and stopped at a subway and had a tuna salad (no bread, in a bowl) as I was staying dry in their restaurant and felt guilty not eating (about 300) calories. Next day the same salad at night and the day after that nothing to eat.
In total I rode for 56 hours in 9 days or 6.22 hours a day. I burned about 47000 calories and took in well under 4000 total. I felt great the whole time and actually forced myself to eat when I did. I rode just over 1000 miles I think.

Its amazing what the human body can do when it is adapted.

Ha ha ha what? I’m going to go with no on that one.

Besides doing 233 watts average for 56 hours over 9 days, that is just so impossible it’s beyond unbelievable. You’d lose 6 kg of fat over those 9 days alone…

I… I’m… lost for words…

I lost 10 pounds. I never said it was smart. Looks like I averaged estimated 244 the first 11 hour day but by the end I was averaging 202. But I don’t have a power meter.

Also when I started the ride I was over 200 lbs with a lot of storage.

A buddy and I did cypress hills last year on fat bikes. About 80 km of incredibly hilly terrain. He ate every 1.5 hours and bonked out hour 6 to the point that he almost passed out. We stopped rested and then rode 2 more hours. I had not eaten for a few days and did not eat that day of riding and was perfectly fine. Difference is I was fat adapted with more than enough meat on my frame. My buddy has i would guess has under 8% body fat. The next day on the way back I forced him to eat every 45 minutes. Had an alarm set and everything.