[scottrogers]

On a 5 hr bike ride your body is going to go into a similar state as intermittent fasting with all your glycogen being burned off. Similar to fasting this frees up energy and allows the garbage in your system to be burned off.

[michaelcampbell]

I do a ~24 hour fast weekly, and a LOT of sites go into this "burning off garbage" or "toxin cleaning" rhetoric which always puts me in "bullshit warning" mode. Is there actual science behind these claims?

[hazeii]

The 'detox' side of it is very likely garbage (but a great way to sell); on the other hand, 5-hour bike rides without fuel will deplete your glycogen stores and there'll come a point where the differnce becomes obvious (see 'bonk-training').

A 24-hour fast is different; your body will burn fat at sufficient rate to avoid glycogen depletion (it's pretty simple; the harder you exercise the less energy comes from fat and more from 'carbs').

From a weight-less perspective though all that matters is calories out exceed calories in - it's quite possible though that fasts end up making you less hungry than hard exercise does.

Long-distance cyclists don't worry about any of this though - the approach is actually pretty simple:-

Press food to face.

Suck.

Repeat.

Edit: formatting.

[_0w8t]

In one of his articles Ray Cronise gave some numbers that even with light jogging or even fast walking for fuel body uses carbohydrates exclusively. So cardio exercises are a bad way to loose weight. They made people hungry. And as people eat all the fat from the food is stored as body fat and may not be burned until the next exercise.

[hazeii]

That's pretty much it; although at higher intensities the calories per unit time is higher, the higher the intensity the more comes from short-term stores (glycogen) than from long-term (fat).

The numbers suggest 60 to 70 per cent of max heartrate (which is pretty easy) is the sweet spot for general fitness and fat burning (i.e. weight loss). For improved endurance, spend a lot of time in that zone; for improved performance spend shorter periods (well) above it.

[jryan49]

The only thing I've read that doesn't completely fire off my "bullshit warning mode" is something like "fasting can enable stem cells, and have immune system destroy old cells" like explained here: https://www.telegraph.co.uk/science/2016/03/12/fasting-for-t...

Still seems a little too "high level" to actually believe though. In any case, I still do IF by skipping breakfast, mostly because I'm lazy, and after fasting for so many years hunger doesn't really bother me that much.

[RBerenguel]

Fat tissue is a collector of some kinds of toxins (don't remember exactly which now) and some heavy metals (heh). Going into fat burning actually releases these into your system (which should be bad, though)

[Pete_D]

Are you thinking of https://en.wikipedia.org/wiki/Persistent_organic_pollutant ?

[RBerenguel]

Yup that was it, thanks!

[Pete_D]

These kinds of claims when made about fasting are IME usually talking about autophagy. https://www.niddk.nih.gov/news/archive/2013/working-out-heal... is the least shady synopsis I could find. That mainly talks about exercise - for fasting, people seem to be most interested in the mTOR pathway. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3266408/figure/...

I'm not qualified to judge the literature as a whole, and it appears to be an open question whether this can be translated to actionable advice, but we're not in complete bullshit territory here.

[RobertRoberts]

Years ago I attended a health seminar where the presenter stated that the digestive system uses lots of energy to digest food. He (and other authors I've read) suggested the idea that generally speaking, when your body doesn't have to spend energy digesting it can do other things better. (ie, detox would fit in with this) Though I can't say I understand how or why this would work, it's seems a reasonable assumption.

[_0w8t]

I read some Russian articles about research carried out about 40 years ago about the most efficient way to survive on limited food if one gets lost in wild nature. Their conclusion was that one should not ration food. One should just eat normally until one runs out of food and then fast until normal amount of food is available. And fast here means literally zero calories. One should not eat berries, mushrooms etc. Those triggers digestion that spend more energy that will be extracted from snacks.

[dominotw]

> garbage in your system

What precisely is this?

[rimliu]

Garbage statement. Your body is not an incinerator. Kidneys and liver take care of the garbage.

[OldSchoolJohnny]

Lymphatic system, which operates during movement.

[nradov]

Most athletes doing long bike rides consume carbohydrate supplements such as sports drinks or energy bars. Otherwise unless you're going at a really slow pace you'll "bonk" after a few hours and be physically unable to continue.