Intermittent fasting

Anyone have any references to studies that have looked at endurance athletes and intermittent fasting? I have read a lot about the benefits of intermittent fasting for “normal” adults but am interested to see if it is compatible with the nutrition requirements of endurance athletes.

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I’ve been experimenting with this, and am curious as well. I’ve found I need to fuel for rides harder than sweet spot. I normally work out in the morning, and that is also when I’m not eating. I still have a lot to figure out with this - I’ve old been doing the time restricted eating for a few months, and have been more flexible in my training during that time as well. Come early next year when I’ll be more focused on training I’d like to have a better understanding of how to mix the two.
I don’t race, and am more focused on longer, study state efforts, so I think it could work for me.

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I IF most days, not eating from around 7pm till mid day the following day. If I’m in my easy week I will train fasted but when in the tougher weeks of a build I will train after I have broken the fast.
I will usually eat something on weekends before a longer ride and or make sure I have had some quality carbs for dinner the night before.
As for studies, I’m not sure although fasting has been linked to longevity Dr Volter Longo, (spelling could be wrong) and there is a guy Tyler Tolman who does a lot with IF as well as extended fasting and juice fasting.

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I used to IF religiously during my GymRat days (6-7 years) and did a little more loosely the last year or two.

I’ve tightened things back up the last fortnight and am actually trailing 24hr fasts/OMAD the last week.

Slipping back in to the regime has been seamless for me. I did some Fat Adaption work on the bike 2 years ago and had never been (nor needed to be) a big eater in the saddle but that doesn’t undermine the need to be properly fuelled for workouts and to recover & eat well.

My last 4-5 rides of varying intensity and duration (up to 4hr aerobic) have been fully fasted without detriment.

Already cited here but Dr. Jason Fung’s ‘Fasting Guide’ would be a useful read. I’d be keen to see some more cycling specific studies with regards to fasting than LCHF per se.


awesome. I’m going to check out that guide.

It’s mostly anecdotal evidence for now when we’re talking about athletes. There’s some studies but frankly, there’s not enough data. They’re working on this question as we speak.

Prior to this, the best data we’ve had is on Ramadan protocol intermittent fasting on athletes and if you do a google scholar or pubmed search you will find plenty of articles. They mostly focus on the detriment of Ramadan fasting, which isn’t much. Some show some detriment in athletes from such a fast, others conclude that there aren’t major detriments.

Free-living participants were able to comply with 14 h of daily daytime abstinence from food and drinking for 28 d with only a minor effect on body mass index and without any effects on body composition, glucose metabolism, and cognitive function.

My hypothesis is that your mileage will vary depending on what level of athlete you are. Having a blanket recommendation for intermittent fasting may not be appropriate. I also suspect that it would be best to do it in a periodized fashion in which it is timed with your training loads of the season.

If you were my experiment, I would be measuring objective values as to how you are responding to intermittent fasting by measuring weight, body fat, glucose response, sleep analysis, heart rate variability and reports of RPE during workouts. Needless to say, FTP too. :smiley:

There are also many variations of fasting protocols eg. 3 day water only, 14hr coffee/tea ok, 14hr coffee/tea not ok and everything else under the sun.

Personally, I like having intermittent fasting as a tool in my quiver to be used when I want to lose some weight. I find it easy to implement and highly effective. Counting calories isn’t my idea of fun and this is a nice alternative.

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I have to say I have mixed feelings about IF. I read the “Obesity Code” and decided to give it a go. I’ve been on 16/8 IF for the past 7 weeks, eating to hunger but also logging all my meals using MFP to have a good control point.

I also removed all refined sugars from my diet and severely reduced alcohol intake (I basically had 1 cookie, 3 beers and 1 shot of tequila during the past 7 weeks).

I did the Dexa scan at the beginning of the experiment and I’m planning to do another one somewhere in the beginning of next year.

My findings so far:

  • 16/8 fasting is very, very easy. Took me just a few days to adjust, the first fasted 90-minute workout was downright miserable, but a week later I did not feel hunger at all - I would normally have my last meal at 8pm and would break the fast at noon the following day
  • I get more hungry after the first meal than before it, I had to significantly increase the size of my lunch (from 450-600 kcal to 800-900)
  • Eating enough during the day is a challenge, which nearly always ended up with me having a massive evening meal, accounting for 50% of daily calories.
  • My average TDE for the period was approx 2600 kcal a day, daily calorie intake varied greatly between each day with some days under 1500kcal, some days above 3500kcal.
  • I ate less on training days, way more hungry on easy/rest days
  • My HRV increased, resting HR decreased significantly (from a baseline of 46 bpm to 38 bpm)

Now the results so far:

20 September: Weight 79.1 kg, bf% dexa: 18%, bf% skinfold: 14.8%, FTP 290W
31 October: Weight 79.1kg, bf% skinfold: 14.8%, FTP 272W (not planning to do dexa for the intermediate checks)

I was honestly hoping for some improvement, looking at my net calories I did have a total of 6000kcal deficit in the 7 weeks, which quite possibly got offset by reduced metabolism. Initially the weight dropped to under 78 kg, only to creep up in the last couple of weeks back to exactly where I started. FTP drop is quite worrying too, but it’s the off season and part of it is me forgetting how to hurt on a trainer, I’m not too concerned about this. I’m now having serious thoughts about pulling the plug on my little experiment and just sticking to what I know worked for me in the past. I don’t know how else to interpret the resting HR drop as my metabolism slowing down, it’s definitely not due to any improvements in aerobic capacity and heart stroke volume, I’m just at the beginning of base phase.


I looked into it as a methodology. For weight loss, the only science I could find to support it as a methodology was that it was another way of restricting calories/ working to a calorific deficit. Which from all my research is the only scientifically backed way of losing weight - IF; Low Carb etc., help people lose weight by creating a deficit, so whatever method works for the individual is my take.

It’s been suggested it can help reduce excess skin that people have if they’d lost a lot of weight, but when I read up on that aspect, it was pretty much anecdotal. A medical doctors anecdote does not equal scientifically supported for me.

I know a few audax riders who swear by the whole fat adapted thing, but I remain to be convinced it has proper scientific backing. Obviously, that’s long, low intensity rides though.

Wow, thanks for all that info. Very interesting! I found this anecdote to be telling along with your diet and heart rate changes.

This sounds like you’re not fueling enough for your workouts.

How are you timing meals and macros with your training rides? Are you riding fasted most of the time, all the time, or not much?

With the heart rate stuff, it sounds like you’ve changed a couple of dietary things that would contribute to higher HRV and lower resting. Less alcohol, less simple carbs, IF will all contribute.

Have you tried fast carb supplementation during training? Was that IF for 7 weeks? If so that may be overkill. Some of the benefits of IF is to stimulate autophagy but once you go past that you might be compromising your training. Having enough fuel for quality workouts is usually the higher priority. The weight loss comes with a higher quality diet. Periodized IF is more like icing on the cake here.

Thanks for your reply @Minty_One. To answer your questions:

  • 2 fasted rides a week (in the morning, followed by lunch at noon), I did all the other rides in the late afternoon, 2 hours after the last meal.

  • IF for full 7 weeks indeed, I slipped a couple of times due to life commitments but in general it was super easy and I feel I could definitely do this nearly forever, I don’t miss my breakfasts.

  • I’ve consciously not done any fast carb supplementation during training, just abstained from simple carbs altogether. I was also significantly dropping my training volume at that time, so the longest intensive workouts were like 90 minutes, I did not feel carb deprived during those.

All in all, I think IF may be very helpful in some cases, but it’s pretty much a personal thing - fasting and eating to hunger seems to work less than ideally for me, as I will replenish the caloric deficit no matter what, doesn’t matter how long or short the eating window is.

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Thank you for sharing your experiences with this! I tried intermittent fasting for a couple of weeks in 2017. This was also after having read the obesity code.

I feel like my experience with the results is somewhat similar to yours. Especially during the beginning I didnt find it that hard to skip breakfast. Only sometimes I ran into issues with late night training → late night snacking/“recovery meal” → keeping 16 hours fasting window afterwards, well into the afternoon.

Like you, I also noticed that I don’t have much issue eating all the Calories in 8 hours. After working out, I would regularly be able eat a 1200-1500 Cal. lunch.
Now I’m back to splitting those between breakfast und lunch and actually doing somewhat better with hunger management, and especially regarding performance on the bike. What I still took away from the Obesitiy Code were the general insights into insulin (resistance). I try to not eat anything after 8 pm and before breakfast and also limit snacks between meals. Together with generally high diet quality this enables me to keep a deficit. I adjust this as necessary, i.e. big lunch planned at the office equals light breakfast.

Regarding the findings by Dr. Fung or the “carbohydrate-insulin model” in general: There is some controversy around it, like with all things nutrition…

Stephane Guyenet (who is the author of a very interesting nutrition book himself: The hungry brain. Strongly recommended, also looks at underlying factors like palatabilty of food and societal factors that make people overeat) wrote this article: Why the carbohydrate-insulin model of obesity is probably wrong - which does not reference Dr. Fung directly but debates a lot of the reasoning he uses in his book, like the harmful effects of carbohydrates in general and the Glycemic Index/Load.


Thank you, this is very interesting. I did not know of Stephane Guyenet before, I’m definitely going to check his article now. I guess there goes my productive work afternoon :slight_smile:.

Hrmm, with what I can gather you would’ve been an ideal candidate for losing some %bf from IM and with 7 weeks, there would’ve been results. Given all the data provided, I do think there’s something you can optimize here and that is to periodize your feeding. Rather than focus on the hours without food and eating to hunger, really let yourself get hungry and then, go past it. Usually, there is a dip to overcome but once you get to the other side, the urge to eat disappears. Generally, most of us have enough fat stores to last a few weeks to a month without food, so eating is somewhat of an option.

One of the tricks to IM and weight loss is that, for most people, it’s a way to decrease caloric load whether they’re conscious of it or not. If you are doing a complete refuel and, with the lack of progress on the %bf front, you may stand to gain by doing a tangible caloric restriction through fasting.

The periodized part of this method is on training days you only fuel right before your workout. So, for example, when I do a late afternoon workout I am abstaining from food all morning until mid afternoon, about an hour or two before the ride.

If there is anything to be gained from this, it’s this! You have trained your body to be more resilient in the face of liver glycogen depletion. Although this is not the same as muscle glycogen depletion, as I assume you are eating carbs the night before, this type of resilience is useful in fighting that mental “bonk” feeling. The trick is, on longer rides and races, you have to be extra diligent in proper fueling.

All good points! Just to clarify and correct your assumption: I currently do 2 fasted rides a week, Wednesday is a shorter (60-90 min), carb depleted ride after an intensive Tuesday workout with just protein and a salad the night before (e.g. salmon and spinach). Saturday is a longer (2-3 hrs) fasted ride with moderate carb intake the night before. I already posted in another thread on how well it worked out for me 2 seasons ago and it’s really good to see how quick is it to regain the past adaptations.

Back in 2016 the first 4 weeks were a struggle, this time it all came back after literally 1 ride. The second workout was just fasted, not depleted - I was planning to do some easy endurance but legs felt great and I ended up spending 25 minutes above threshold out of 2,5 hours of total workout.

I definitely see the added value of fasted training and will keep doing it during my base phase, but I think I will just stick to clean food and normal meal schedule on the remaining 5 days of the week. I have quantifiable results that this approach worked for me in the past (that fat oxidation curve from my topic really speaks for itself), I was just hoping that IF would make even a bigger difference but that’s not really what I’m seeing in practice (based on my own example).

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Ah, so you did go for muscle glycogen depletion too! Well it looks like you covered a lot, especially with all that data in your other post. It’s too bad that you don’t seem to be a high responder to IF. Were you trying to lose body fat with your protocol?

I’m curious , how come you were doing so many fasted rides (>90%) in 2016?

This guy should no a thing or two about fasting and nutrition on a bike.


Yes, mostly trying (and succeeding) to lose body fat.
Long story short, I had a bike crash during training and spent the subsequent months not being able to ride my bike due to a hand surgery and complications. I saw this as an opportunity to focus on weight loss, started with the Racing Weight Quick Start guide where I learned about the benefits of occasional fasted workouts. It reacted to this training pretty well and found myself not needing to fuel before my workouts and due to being indoors they were short enough not to require fueling during.
I don’t recommend this approach to anyone - this really caused me a lot of trouble when I finally could do long intense rides where carb supplementation was essential.

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Yea I saw in the other thread, it seems like the sacrifices of being more fat adapted may have sacrificed your carb absorption/utilization abilities. I saw the charts and calculations, which seem accurate but it just doesn’t add up to me. I didn’t even know that was physiologically possible to use that little fat. Sorry :frowning_face:

I really would question it. You’d expect to see some low% of fat but not 0 at the low efforts. You’ve got some power in you so you have to be well trained and to be so carb heavy, that’s nuts. If everything about those results are true, are you thinking that your low hanging fruit is to work on utilizing fat as a fuel? This would be a multi month/year experiment, but I wonder what would happen if you went keto. If your baseline is really so carb heavy, what was your lifetime diet like? I find this…fascinating…

I tried Keto [almost zero carb] for a while. Lost a lot of power and HR was much much higher thru the rides. Back to a slightly reduced carb diet with intermittent fasting now.

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Yes it’s interesting that he is following this approach. Especially as he probably has some of the best advise and coaches in the world to help him. I wonder if trainer road could get sir Dave on the podcast one day!!:thinking: