Cycling, carbs, the bonk and ketones - in that order

[horizon]

This might have been discussed at length already but if anybody has anything to say on the issue that would be very helpful. My query is triggered by this article about a new ketone drink:

https://cyclinglegends.co.uk/index.php/ ... ret-weapon

but I'm more interested in what happens at the point (if I have got this right) where the body switches from using glucose for energy to ketones. AIUI, once the body has used up its reserves of glucose, you are in "bonk" territory unless or until the ketones kick in (or you've consumed more carbs/sugar). I think cugel alluded to this in a recent post but I'm afraid I cannot find the link.

[Jdsk]

I hadn't read that article before. It's hard to make out from it what's actually known. And there's a product being marketed.

There has been some advocacy of ketosis in this forum but not recently.

The scientific paper to which they refer is probably:
"Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes"
Cox et al, 2016
https://pubmed.ncbi.nlm.nih.gov/27475046/

Jonathan

Statement of interest: I've worked in some of the laboratories mentioned in the authors' affiliations and with some of the researchers whom they cite.

[Jdsk]

... but I'm more interested in what happens at the point (if I have got this right) where the body switches from using glucose for energy to ketones. AIUI, once the body has used up its reserves of glucose, you are in "bonk" territory unless or until the ketones kick in (or you've consumed more carbs/sugar).
...

In most humans that won't be a sharp point, more a transition. I've never seen a clear explanation of what happens in real-life bonking. Many of you will have experienced rapid recovery with ingested carbohydrate. But sufferers aren't usually hypoglycaemic. And different organs preferentially use different fuels.

I may be out of date on this. It's some time since I worked in a laboratory that studies fuel selection, and even longer since I worked on exercise physiology. All updates appreciated.

Jonathan

[re_cycler]

I think this is a review of some of the more recent published articles.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9734240/
At a high level isn't bonking just glycogen depletion ?

[horizon]

At a high level isn't bonking just glycogen depletion ?

Yes, but I think the question is what happens then. Simplistically AIUI, you just need to eat a lot of carbs equal to the amount of energy you intend to/are expendng. But, again AIUI, the body can go on to use ketones (i.e. fat burning) in order to continue the exercise. This is a slower process (am I right?) and will only kick in after a while and not while you are in max heart rate.

[Cugel]

This might have been discussed at length already but if anybody has anything to say on the issue that would be very helpful. My query is triggered by this article about a new ketone drink:

https://cyclinglegends.co.uk/index.php/ ... ret-weapon

but I'm more interested in what happens at the point (if I have got this right) where the body switches from using glucose for energy to ketones. AIUI, once the body has used up its reserves of glucose, you are in "bonk" territory unless or until the ketones kick in (or you've consumed more carbs/sugar). I think cugel alluded to this in a recent post but I'm afraid I cannot find the link.

Cugel knows of the bonk only too well but the only ketone knowledge I have personally involves the smelly breath caused by it when one foolishly diets too hard. Isn't it some sort of by-product of your bod burning fat as the primary energy source, once glycogen has been sucked out of yer blud and liver by your mitochondria going like the clappers?

As J mentions, a product suddenly appearing with some sort of magic go-faster thing supposedly in it, whatever they choose to call it, is always suspect.

[Jdsk]

...
At a high level isn't bonking just glycogen depletion ?

It's connected to that, but there just aren't enough observations to show how that is connected to the effects... what's going on in muscle and brain? (Same disclaimer that I might be out of date,)

Jonathan

[Jdsk]

I think this is a review of some of the more recent published articles.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9734240/
...

And notice the reservations in the Abstract and the Key Points: there aren't consistent observations of benefit to performance or recovery.

It's also very good on the sort of research that would make a difference to what we know.

Jonathan

[re_cycler]

I think this is a review of some of the more recent published articles.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9734240/
...

And notice the reservations in the Abstract and the Key Points: there aren't consistent observations of benefit to performance or recovery.

It's also very good on the sort of research that would make a difference to what we know.

Jonathan

Very true, more research is always useful.

Edited to remove pointless comment

[horizon]

Cugel knows of the bonk only too well

My reference was to a post you made recently in which you advised someone who was enquiring about the bonk. You said (IIRC) that in time, longer distances would be possible without the bonk and that one's body would adapt (as it does indeed seem to do for people who cycle long distances).

Do you by any chance remember your post?

As J mentions, a product suddenly appearing with some sort of magic go-faster thing supposedly in it, whatever they choose to call it, is always suspect.

I agree - I think it is totally suspect as what I am referring to is a normal process that happens anyway (well, that is the question I am posing).

[Cugel]

Cugel knows of the bonk only too well

My reference was to a post you made recently in which you advised someone who was enquiring about the bonk. You said (IIRC) that in time, longer distances would be possible without the bonk and that one's body would adapt (as it does indeed seem to do for people who cycle long distances).

Do you by any chance remember your post?

As J mentions, a product suddenly appearing with some sort of magic go-faster thing supposedly in it, whatever they choose to call it, is always suspect.

I agree - I think it is totally suspect as what I am referring to is a normal process that happens anyway (well, that is the question I am posing).

My experience over decades is (as it seems to be with most cyclists doing lots of miles) that one's bodily processes seem to adapt, particularly in being able to somehow turn up whatever the mechanisms are for using body fat as an energy source. I did once get the explanation from another cyclist who did a sports science degree but I can't remember the details at all now, other than that cycling for long distances at a relatively low energy level seemed to "teach" the body to use both glycogen stores but also fat stores in a way that combined the two, rather than burning all the glycogen first before starting up the (relatively slow) fat utilisation.

Even just 5 years ago, when I was 69, a couple of years going out with the club and doing 120 - 180 miles a week at club run pace (for ex-racing ole pharts) I often found that I could do significant distances and climbing without eating - as long as I'd had the porridge or whatever before going out. I once did a 60 mile continuous ride (didn't stop with the rest at the cafe) with no bonk despite only drinking lots of water from the bidons but eating nothing during the ride. I was certainly ready for tea when I got in but only in the normal feeling-hungry way.

Some of us seem to have, perhaps genetically, better mechanisms for storing and using body fat than others. It may have something to do with the way body fat is stored. Mine goes on everywhere over my body rather than seeming to concentrate mostly around the waist. It also seems to come and go quite readily, whether through eating more/less or exercising more/less.

But when I (or anyone else) gets the bonk, one's breath does smell of what I'm told are ketones. The smell is very distinctive.

[531colin]

…..,,,,,,I've never seen a clear explanation of what happens in real-life bonking. Many of you will have experienced rapid recovery with ingested carbohydrate. But sufferers aren't usually hypoglycaemic. …….

Bonk recovery can be very quick ….., I wonder if it’s too quick for absorption of even simple carbohydrates. Could recovery be redistribution of carbohydrates from glycogen stores to muscles?
But if you aren’t hypoglycaemic why does it feel so b. awful?

…………..

My experience over decades is (as it seems to be with most cyclists doing lots of miles) that one's bodily processes seem to adapt, particularly in being able to somehow turn up whatever the mechanisms are for using body fat as an energy source. ………

Yes, I think you can “get used to” doing a lot of miles without guzzling energy gels every few miles…… and I think that implies that your muscles become “trained” to
metabolise fatty acids.
Just one more thing I can’t remember; do the different muscle fibres have different preferences for metabolising sugars or fatty acid?

[Gearoidmuar]

I'd put in a long reply but managed to delete it, so here's a precis.
The bonk is caused by a rapid drop in blood glucose, not necessarily to hypoglycaemic levels. The old advice to eat mostly carbs on the bike is wrong. Mixtures, such as cheese sandwich work much better. This I established over many years doing longdistance training.
For 10y I've not had the bonk once. I'm on a lowcarb high fat diet for that period, keeping 38lb off. I stayed on the diet because it completely cured me of depression.
I've twice done Lejog before diet and after.
On low carb you will slow down a bit as you run out of glycogen, but not much. You can prevent this by taking some good carb (plain potato etc) at the end of your breakfast.

If you don't want to do lowcarb, my advice is to not eat junk food. It increases your appetite.

[LittleGreyCat]

There are two different aspects to this:

(1) You start out using glucose as fuel, then switch dynamically to using ketones - this can be difficult to impossible for some people. You can have more initial energy but less stamina. The switch over point can be harsh.

(2) You start and remain in ketosis - that is you have been eating very low carbohydrate so that your body has to produce ketones for your basic daily energy requirements. This IMHO is a better way to operate. You have less initial energy but more stamina. You don't have the pain of transition between energy modes.

I have read that there is a point where your gut cannot take on board enough food (even gels) to replace the blood glucose being used and that is one cause of the "bonk" in riders who keep hydrated and fed. If you are already burning body fat then you don't run out of fuel.

When I'm cycling fit and eating LCHF I can cycle reasonable distances on just a cup of coffee with butter and double cream.
That is, at least 1-2 hours which for me would be 20 miles+.
Cycling companions are desperate for cake after about 1 hour.

There are references such as :
https://www.amazon.com/Art-Science-Low- ... 0983490708
https://www.amazon.com/Art-Science-Low- ... 983490716/
which are quite old now but lay out the basis of Low Carbohydrate living and exercise.

[horizon]

There are two different aspects to this:

(1) You start out using glucose as fuel, then switch dynamically to using ketones - this can be difficult to impossible for some people. You can have more initial energy but less stamina. The switch over point can be harsh.

(2) You start and remain in ketosis - that is you have been eating very low carbohydrate so that your body has to produce ketones for your basic daily energy requirements. This IMHO is a better way to operate. You have less initial energy but more stamina. You don't have the pain of transition between energy modes.

AIUI, the body uses glucose for heavy-duty, anaerobic exercise - you tear off at speed, keep up a fast pace and charge up the hills. Obviously, you then have to re-charge quite soon.

Alternatively, you set off at a moderate pace, use some glucose to get you going and then transition slowly to ketones. A sprint up the odd hill might involve a burst of glucose but then you are back in steady mode. So really this transition depends not so much on your existing diet/regime but on your approach to the riding itself - you pass seamlessly through the bonk.

I'm wondering though whether you would actually have to forego the carbs on the ride itself in order to allow the body to go into ketosis and this I presume is the harsh transition you refer to.