Intermittent fasting not so good? - new study suggests it isn’t

Article and paper links below - it seems that intermittent fasting may be bad for performance, although the study participants are not cyclists I would imagine muscle loss may well be a risk to cyclists as well.

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It’s never really been supported by science, bar being a method to get a calorific deficit (that some find sustainable).

There’s been some research suggesting other benefits, on things like gut health, but nothing that has been proven.



I found skipping breakfast an easy and sustainable way to drop 20 kilo. (although in the end I did add on some more weapons to my arsenal, like carb restriction on non training days)

My (strength) workout routine made sure muscle loss was minimal.


As a disclosure I only read the abstract of this article, my institution only gets me access to JAMA articles that have been printed and not the online first articles. I also only did a cursory search of the literature on the subject and am open to correction if I am wrong.

This is an interesting article and from what I can see one of the biggest human trials on the subject. This certainly suggests time restricted eating (TRE) is not as effective as some people claim. However, from a purely academic standpoint we can’t interpret this article as saying time restricted eating decreased performance. The article did find that TRE decreases muscle mass and it certainly makes sense that it would decrease performance but that is not what they studied. One article I found actually studied this exact question.

They studied middle and long distance runners split into a TRE group and control group. The study found that TRE resulted in weight loss (although they did not look at lean muscle mass). No change was seen in several endurance performance measures (O2 consumption, respiratory exchange ratio, lactate, HR). One interesting finding was decreased daily energy in the TRE group. Some limitations of this study is that it is very small, n=23. They only studied the athletes for 8 weeks so we don’t know what happens after. These were also young healthy males so we can’t expand that to the general population.

I think the JAMA article certainly gives us some insight into the effects of TRE that should be considered by endurance athletes and opens up topics for future research into this relatively new diet trend.


Interesting. Fasting and performing don’t sound like they should go together. Was the thinking that IF should be for off-season body composition changes or base to make the body use fat for fuel? Now that’s out too?

Fasting over night is enough for me. 9-10 hours or so without food or drink seems like my maximum, only achievable while I am asleep! :drooling_face:


I think most studies indicate that IF and general calorie reduction are about the same as far as weight loss goes. I can personally get behind some of the ideas of that (like cutting myself off after a certain time because I can snack forever). But I’ve seen way too many big claims on the benefits of IF, and a lot of people talking about more theoretical things (like autophagy) as if it were established fact.


Iirc the concept of this first came about as it showed a reduction on cancer markers *- women who followed a 5/2 could reduce their risk of breast cancer by about half.
Then weight loss groups etc all jumped on the bandwagon.
So not surprising that it doesn’t support endurance athletes. :joy:

I lost 50 pounds in a year. The first 30 pounds were using the 18 hour diet (cheating one day per week). The final 20 lbs were from just eating better and riding more. I have kept it off for almost 2 years now. (But I did gain 5 pounds since lockdown, haven’t we all?)


I’d never question that it works for some people for weight loss. But it is simply through calorific deficit, not the unproven other benefits IF claims. The gut health possible benefit is interesting, but far from proven at this point.

For me, I tried it as a method for weight loss, and it just wasn’t sustainable for me. I get too hangry.

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I tried fasted riding into work a few years back. I found the loss of performance quite considerable and it promoted a desire to eat more through out the day after (constant snacking), but I also found out subsequently at the time I had bowel/colon cancer so I can’t really judge. I’ve no desire though to do it again though to find out.

TLDR: IF can go along well with professional and athletic success. Guess there is no single truth to it.

I am basically doing IF (16/8) since I am 7 or 8 years old. Obviously, at the beginning absolutely unconsciously. I simply didn’t want breakfast. I kept it that way.

Back then it didn’t affect my academical and athletic endeavors. Quite the contrary actually. Over the years I was quite successful in soccer, swimming, and martial arts. Ditto for school and later university.

While I eventually stopped all that in my adult years, I have kept the 16/8 routine. Again, it had no effects on my now professional career and athletic performance.

The latter is actually getting better and better (4.5 watts per kg for instance sake). Doing a two hour sweetspot session like Wright Peak followed by a hour run is no biggie “fasted”. Obviously, it’s even less a biggie loaded up with carbs. Though it’s certainly not a necessity.

Obviously, this is just my n equals one. Though it makes me believe that those generalizations like “this is good and this is bad for performance” aren’t valid. There is much more to athletic success that nutrition. Also there is no absolute truth to nutrition. At least not to my understanding. I would say do what works best for you.


What are the effects of incorporating fasting for 1/2 workouts a week

Once a week i’ll not eat until my workout (1hr Z2) which is at about 5:30PM, are there any downsides to this?

I can see the benefits for someone trying to lose weight in a hurry but it’s not my cup of tea. I like to eat, I like to ride hard, riding hard on an empty stomach is generally a terrible idea IMO. I’ve done it before, and felt like crap the entire day after.

I’ve been curious to try it, but I don’t understand how people who have to train early in the morning like myself can swing it and still hit their intervals on empty. Not to mention not taking in anything afterwards for recovery when many experts say it’s the most efficient time for protein and glycogen synthesis. If I were able to train in the afternoon during the “feeding” time, it might make more sense.


@Charlie_Botterill I wouldn’t expect you to experience any downsides when doing one or two fasted endurance sessions per week. Quite the contrary. The team has covered this in multiple podcast episodes. Don’t ask me which though. :sweat_smile:

@SexyCoolguy Assuming you have a proper dinner the evening before, you will wake up with topped up glycogen stores. Plenty to get you through the first 30 minutes (likely much longer). This was also on the podcast. :grimacing:

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Dr Rhonda Patrick promotes fasting for apoptosis, cell death. It is another function of our bodies that cleans out the junk. My basic understanding is when cells corrupt their DNA coding they can reproduce with the faulty coding. Enough of that can lead to a cancer growth. Fasting induces apoptosis which kills off the evil cells and promotes healthy cells. Don’t ask me how it does it, I just trust she has done the research and it just works.

I’ll be adding some fasting to my winter health protocol cause I want to be a TR user at 100. If you can’t ride faster than others in your age, out live them. Is the a US National Mountain Bike Champions Jersey for over 100?

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Yeah, but what do you do for the remaining 60 minutes, eat your arm? I guess that would be technically breaking your fast.

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It seems like you guys are conflating IF, fasting, and fasted training. They are all different things.

IF is an eating window. Like you only eat in an 8 hour window. And there are tons of variations. People lose weight doing this because they are restricting the hours in which they can eat. Studies show that most people overeat by a small amount every day - like 200 calories per day. Thus, you could stave off the creep up in weight as you advance in age if you don’t overeat day in and day out by a small amount.

Fasting is simply fasting and you don’t get significant autophagy until 3 days in. I’ve read a lot about fasting and have only done a 24 hour fast myself. It’s easier than you would think. Fasting seems to have other benefits like the mentioned autophagy, gut immune cell regeneration, etc.

Fasted riding is not a make you faster thing. Usually it’s a weight loss strategy.

If you guys want to learn about carbohydrate periodization. I’d recommend you read and listen to John Hawley and James Morton. They have been on tons of podcasts and have written many papers. The protocol that sounds the most interesting is the train high, sleep low protocol. For example, do your intervals in the afternoon fully fueled but then severely restrict carbs for the rest of the night. You can still eat protein and fat.


So an interesting point from the abstract (scihub still doesn’t have a copy of this paper), but they mention the IF group was eating ad-libitum while the control was eating “3 structured meals”. What I think they mean here is the control group had their calories controlled at each meal while the IF group got to at as much as they frickin wanted, as long as they stuck to the window. I know this is a hottake, but sure sounds like the IF group significantly outperformed the control diet given calories weren’t controlled.

CICO. Nothing more, nothing less.