How fast do we metabolise?

[Sweep]

I never gobble any sort of energy bars. They are just sugary junk food. If you eat a decent breakfast, lunch and evening meal you shouldnt need these things unless you are some sort sort of racer. I have learned that its mental attitude, correct gears and appropriate pace that helps you on hills.

Al

I know where you are coming from al but it is vital to avoid the bonk. You should always have some sugar of some sort with you I think on a long hard ride - otherwise you have to rely on my sort of luck - once bonked on a verge and was lucky enough, looking heavenwards, to find an array of blackberries in the hedge. Lay there for 10 minutes plucking them and trying to look cool. I have been known to carry 3 bags of Lidl wine gums. Not health food I agree but much appreciated/needed.

[Psamathe]

I never gobble any sort of energy bars. They are just sugary junk food. If you eat a decent breakfast, lunch and evening meal you shouldnt need these things unless you are some sort sort of racer. I have learned that its mental attitude, correct gears and appropriate pace that helps you on hills.

Al

I know where you are coming from al but it is vital to avoid the bonk. You should always have some sugar of some sort with you I think on a long hard ride - otherwise you have to rely on my sort of luck - once bonked on a verge and was lucky enough, looking heavenwards, to find an array of blackberries in the hedge. Lay there for 10 minutes plucking them and trying to look cool. I have been known to carry 3 bags of Lidl wine gums. Not health food I agree but much appreciated/needed.

So, a bit off topic (mods please do split to a separate thread if appropriate), avoiding bonk one thing but what do people do once "bonked"? And what sort of warning do you get you are approaching the bonk?

Ian

[NATURAL ANKLING]

Hi,

Not sure I agree, Vorpal. I don’t know how it works biologically, but sugar starts kicking in long before 20 minutes in my case.

Probably right according to piece of research, which shows glucose level raised well above baseline at 15 minutes after a meal.

https://watermark.silverchair.com/97.pd ... lYvh-An0ty

I was always led to believe that glucose goes into blood through stomach?

[Mike Sales]

So, a bit off topic (mods please do split to a separate thread if appropriate), avoiding bonk one thing but what do people do once "bonked"? And what sort of warning do you get you are approaching the bonk?

Ian

The warning is rapidly increasing weakness, and when I first bonked, on an icy day, an inability to keep warm.
The only remedy is getting outside of food. Rapidly accessible items like sugars work well I have found, and work rapidly.
On that first occasion I left my bike with my companion, and flagged down a car for a lift to the nearest caff. This was in the Yorkshire Dales and the driver understood my problem, being a cyclist. By the time I had eaten and realised I had no money, my friend had walked there with both bikes and money.

[Sweep]

As above, once bonked, get some sugar in me quickly.

It's only happened to me a couple of times and not for a long while, basically because, forewarned, on a long ride I regularly snack - homemade cycle snack (mix of fast and slow release stuff) and, yes, those Lidl wine gums.

First signs of impending bonk as I recall were maybe more than expected sweating, certain slowness in reacting to things (hence it can be dangerous) and, as I looked at the speedo, the clear realisation that I was going far slower than I should be on a fairly flat road. I suppose the fact that I had to look at an electronic device to really be "told" that something was up shows how befuddled my mind was becoming. At that point you need to get off the bike for all sorts of reasons.

Another sign according to a doc who used to come on a lot of my rides is folk getting angry, unreasonable, argumentative. He reckoned that the reason there was often a lot of trouble in A&E of a saturday night was not primarily because of alcohol but because of low blood sugar. This topic came up discussing, after the event, a particularly tough ride of mine he'd been on (subsequently billed as "the hell of ......." so that folk couldn't say they weren't warned) where I as the ride leader had a fair amount of aggresion thrown at me in the latter stages - before the entire field abandoned it

maybe you should get round to that ride with me al - if the bonk approaches I promise to dangle a wine gum in front of you.

all the best

[cotswolds]

Probably the minutes rest and the psychological boost of knowing something is in the system.
Question do you really NEED the snicker bar or only THINK you need it?

TBH I would be ill if I had something inside my stomach that close to starting a big climb.

A friend used to have this theory; When heading for the bonk stopping and eating makes you feel immediately better, 1. obviously psychological. 2. He thought that eating something triggered the brain/body to know there was some re-fuelling on it's way so the body could release the last bit of reserves of stored glycogen into the system... so your body got a short term boost while the replacement food was digested and absorbed.

Can't find a link now, but I remember a piece of research that supports your friend's theory. After an initial exercise period, athletes were given a sugary drink which they took into their mouths then spat out. They then measured something (I think it was blood sugar, but it might have been performance) and the figures were better than for athletes who hadn't taken the sugary drink into their mouths. The explanation was that body always has reserves, and will release them if it knows they can be replenished. So you don't actually need to eat the snickers bar, just chew it then spit it out.

[Samuel D]

Probably right according to piece of research, which shows glucose level raised well above baseline at 15 minutes after a meal.

https://watermark.silverchair.com/97.pd ... lYvh-An0ty

Unfortunately I can’t get that link to work.

After an initial exercise period, athletes were given a sugary drink which they took into their mouths then spat out. They then measured something (I think it was blood sugar, but it might have been performance) and the figures were better than for athletes who hadn't taken the sugary drink into their mouths. The explanation was that body always has reserves, and will release them if it knows they can be replenished. So you don't actually need to eat the snickers bar, just chew it then spit it out.

An alternative explanation is that some glucose entered the bloodstream almost immediately via the salivary glands in the mouth. I believe I have felt this happen with caffeine.

[Tangled Metal]

Isn't digestion just a chemical reaction in your gut breaking down the food into smaller chemicals that can pass into your bloodstream to get used by your body? If it's a chemical reaction there will be tastes if reaction that could be estimated / calculated / predicted. Either way you can't get around the laws of thermodynamics and physics to get a better breakdown of chemical chains (as in foods) into chains that hi through your stomach membrane to the blood.

If these reaction rates are slower than you need for sugars to get broken down and absorbed into your bloodstream then you need to consider what effect you are attributing to absorption of the sugars. Could it really be your body releasing last reserves under the signals that more is coming?

Personally I believe there's a placebo effect going on after consuming foods. I don't believe you get an instant inrush of sugars. It's psychological.

[Vorpal]

So, a bit off topic (mods please do split to a separate thread if appropriate), avoiding bonk one thing but what do people do once "bonked"? And what sort of warning do you get you are approaching the bonk?

Ian

I've had the bonk a few times. I had it once when pregnant, and I seem to be a bit susceptible to it since.
Warning signs for me are when I feel light-headed and/or sapped of energy. It just gets a bit harder to get up hills and that sort thing. I also sometimes have sudden cravings (not normal for me) for sweet things or fruit. I'm much more likely to suffer from it if I haven't had enough sleep.

Once I feel it coming on, I have to stop and eat. It's best if I can eat a proper meal. It might be a packed lunch of sandwiches and that sort thing, if I have it with. A cafe lunch, if I don't have a packed lunch. Otherwise, on a ride long enough to induce the bonk, I usually have something in case of an emergency. A packet of sports drink mix, a spare banana, or some flapjacks, etc.

I don't like sports drinks, and I don't usually drink them, but that seems to be the quickest, most effective way to get a bit of emergency energy in me. Carrying pre-measured, powdered mix in an airtight packet is a good way to keep an emergency stash. I would say that it takes me at least 15 minutes to feel the effects, more like 20 minutes most of the time. And that's really just enough to get me home (short distance), to the next town, or a cafe or something. I really do need proper food to recover enough to do any distance.

The worse it gets before I eat a proper meal, the longer it takes me to recover.

Once I've got the bonk, I can hardly turn the pedals; my top speed isn't much above a walking pace. I can keep going for a bit, but I don't do it unless I absolutely have to. I guess there would come a point where I just wouldn't be able to go anymore, and I'd have to call Mr. V or a taxi, or something. A club mate once pushed me the better part of two miles to the cafe. Once I've got the bonk, I can't really go again, until I've sat down and eaten a proper meal.

I've never tried going more than about 15 miles or so in the aftermath of suffering the bonk, but I can do that much, at least, after I have rested and eaten.

I can generally prevent it by getting enough sleep, eating well, and stopping to eat and rest when I start to feel the signs.

[Mick F]

Only once for me.
Lesson learnt.

LEJOG and Back in 2006, and after turning south at JOG, the heatwave that had started in the south of England and followed me north - but behind me - finally caught me up - or did I catch it up?

As I left Helmsdale and headed for Inverness, I was boiling hot. Loadsa water and stopped for refills. After Inverness I was still too hot and after Pitlochry also. I made it to Edinburgh worn out.

Following day, was a short-ish ride to Carlisle, but I was still worn out. As I approached the town, I took a wrong turn, went down a hill realising I'd gone wrong and would have to climb back up it. I was all in and absolutely knackered, dithering and weak and could hardly see straight. I saw a big tree and shade and almost collapsed under it. I phoned home in tears. Nowt Mrs Mick F could do back in Cornwall, but I needed to speak to someone.

I had a molton bar of chokky in my saddle bag, and squeezed the melted stuff into my mouth and within a minute or two, felt almost human and phoned home again to say I was back in the land of the living.

I was starving hungry and was aware there was a chippy nearby, so turned round, headed up the hill, and scoffed steak pie and chips.

Wow!

[531colin]

I think the answer is probably......."Its complicated.........."
Also its half a lifetime since I thought about some of this, so its almost certainly more complicated now than it was when I thought I knew a bit about it.
As already said, there are 2 basic substrates which can be metabolised by muscle. Fatty acids can be utilised for low-level activity. For anything very energetic you need carbohydrate metabolism.
Unless you are starving**, everybody carries enough fat for a couple of days metabolism. I think there are 2 limits on the rate of energy production which you can get from fat, that's the limited rate of metabolism in muscle, and the limited rate of "mobilisation" of fat from reserves, although it can be speeded up a bit by getting your metabolism adapted to metabolising fat.
Carbohydrate is stored as glycogen in muscle and liver, but the stored amount is limited.
Muscle has 2 ways of metabolising carbohydrate; aerobically until the rate exceeds the oxygen supplied by the blood, at this point (some) metabolism switches to anaerobic, which is "incomplete" in that it leaves behind lactate which can subsequently be metabolised aerobically when the energy demand reduces so the blood supply can keep up.
Gluconeogenesis is a process whereby the liver synthesises "sugar" to replace that used up.
Some features of "the bonk" are due to the effect of low blood sugar on the brain. (disorientation, nausea)

In the sixties, we used to recognise 2 conditions; "hunger knock" and "bonk". The difference between these two is as clear as the difference between a muscle twinge and cramp.
For hunger knock, a brief stop for a chocolate bar (or whatever) will get you to the nearest café; bonk will have you sat on the verge wishing the earth would swallow you up. It is very unpleasant.
I guess hunger knock and bonk are different stages in using up reserves of metabolite, but I would hesitate to say that either equated to any particular stage above. If I had to guess, I would say that maintaining blood sugar levels so the brain functions properly is a pretty high priority for your body (there is an evolutionary advantage in keeping your brain functioning). When you are bonking your blood sugar has dropped, so I guess you have used up both muscle and liver glycogen, and your energy demand exceeds what can be provided by fat metabolism and gluconeogenesis.


**Its a little-known fact that the Temperance movement caused energy malnutrition in labourers..... low wages meant a diet low in meat (and therefore high-energy animal fat) they needed the extra carbohydrate in (small) beer to make up their energy requirements.

[Mick F]

Excellent post there Colin.
Excellent.

[Vorpal]

Excellent post there Colin.
Excellent.

I agree. The only thing that I will add is that I think effects can be somewhat different for different people. The bonk for me, feels more like the aftermath of the flu. I mean if you've had a proper flu (i.e. been sick in most possible ways for a week), in the day or two afterwards, when you have started to feel a bit better, but you're as weak as a baby? That's what it's like for me. I don't feel sick, though I get grumpy/irritable, and I usually feel light-headed, as well. So, I can kind of function, for a bit. I've never tested it to see how long; I don't think I'd want to.

And I'm pretty sure that for me, hunger knock is the first stage in using up reserves, and the bonk is rather further down the scale. I guess what I've learned to recognise as a 'warning' is the hunger knock.

[Norman H]

Just to add to what Colin and others have written. I've no idea how quickly energy becomes available after consuming food. In theory glucose is likely to be the most rapidly available sugar for energy production. Firstly because it's a monosaccharide and is able to pass directly through the gut wall but secondly because, as Colin says, it's the fuel of choice for the metabolic pathways that lead to energy production.

Other monosaccharides like fructose and galactose will pass equally rapidly into the bloodstream but will require additional enzyme catalysed reactions before being metabolised for energy. All other carbohydrates will in addition have to undergo some degree of digestion in the gut before they can pass into the blood stream.

That said, the enzymic reactions that catalyse the digestion of complex carbohydrates to simple sugars are very efficient, and for practical purposes I doubt that the differences are significant.

[RickH]

Some, but I don't know how much, sugar can be absorbed directly in the mouth. A recognised initial treatment for a hypo episode in diabetics is to rub something sweet, such as jam, onto their gums.