Loading, Bonking, Hi-Lo GI, the Wacky World of Carbs….

In any endurance sport, getting the right nutrition before and during is very important.  Depending on how hard you are pushing, there may only be a few hours worth of available energy stored as glycogen, so it is important to adopt approaches to maintain that available energy.  Glycogen is a complex form of glucose (essentially a polymer) that is stored in two main places in the body, the liver and in muscles.  There are a couple of approaches people adopt to help:

(1) Traditionally athletes have ‘carbo loaded’ in the days prior to an endurance event, to try and maximise the amount of stored glycogen in the body, and thus delay the onset of glycogen depletion.  Vast amounts of pasta are consumed.  It’s not something I have ever consciously tried to do, though I did eat quite a lot of flapjacks before last year’s Dart 10K 🙂

(2) Consuming carbs during the event.  The endurance swimmer’s method of choice for decades has been Maxim, which is basically a carbohydrate solution chugged every half an hour or so.  The carbs in Maxim (other carbohydrate drink products are available, but tend to be more or less the same) are present as maltodextrin, another glucose polymer.  A little aside for those who like chemistry:  maltodextrin is produced by the partial hydrolysis of corn or wheat starch, and comprises glucose units strung together end to end to make chains of up to 20 sugars long.  Glycogen also comprises glucose units strung together end to end, but in addition has the occasional branch, making it a more complex structure.  Both molecules serve the same purpose though,  acting as available sources of glucose to fuel the muscles, and importantly the brain.  I actually use the carb drink from SIS, for no better reason than the fact that it is sold in Tescos, and Maxim is not.  I also add Ribena for flavour.



Hitting the Wall

If you deplete the available glycogen, and cannot replace it quick enough with what you eat and drink, then bad things happen.  Physical exhaustion ensues, and your brain, which runs off glucose exclusively, goes to pot.  Hitting the wall is also known somewhat quaintly (and amusingly for Brits) as ‘bonking’.  What happens when you hit the wall?  Is all lost?  Well not necessarily.  The body can actually run off more than one sort of fuel, indeed routinely turning over a certain proportion of its stored reserves of fat and protein. But when the glycogen is exhausted, and the body is required to use those sorts of reserves to the exclusion of glycogen, then things become, well harder.  It should be remembered though that the provision of energy from feed before and during the event, and glycogen and other reserves stored in the body, is one big equilibrium.  It is an equilibrium that the body, under normal circumstances, is exquisitely good at maintaining.  Only when the system is put under a significant stress, 10 hours in to a marathon swim in cold water being one of them, do things typically go awry.

Keto Adaptation

Some endurance athletes employ a strategy to deal with hitting the wall called keto adaptation.  They cut carbs out of their diet completely or almost completely, following a protein and fat only regime.  The theory is that the body becomes used to metabolising those two energy sources preferentially, and also becomes more efficient at mobilising stored reserves of those energy sources.  Now most people, and definitely most cold water marathon swimmers, have fairly ample reserves of fat to draw upon, and becoming more efficient in mobilising those reserves should, in theory, avoid the situation where the wall is hit, and a slow and painful transition has to be endured.

A Diet Free of Carbs

So how easy is it in practice to maintain a diet low, or free, of carbs while maintaining a training regime commensurate with getting across a major channel in cold water?  This, I think, is the crux.  In the run-up to a major channel swim, the athlete will be spending many many hours, swimming in cold-to-cool water, using up massive amounts of energy.  There are the calories required to propel the athlete through the water, and the calories required to keep the athlete warm.  These need to be replenished, otherwise the athlete is likely to become more lean, as fat reserves are used up, and the valuable ‘bioprene’ that keeps him warm in the Channel will diminish.  I know of at least one swimmer who has suffered from this.

Alternative Sources of Carbs

Maxim, or one of the many equivalents (Maxi, Perpetuum, SIS etc etc) is the staple food of many marathon swimmers.  Loneswimmer has described it as ‘rocket fuel for swimmers’.  Can’t say I’ve ever felt that rocket-propelled myself, but there’s always hope.  The maltodextrin it contains is fairly rapidly processed in the gut to glucose that the muscles and other organs are craving.  There are places to go if you want carbs that are more slowly assimilated by the body, and later in the transit of food through the gut.

Low-GI Foods

GI, or glycaemic index, foods are those that are slowly processed by the body to sugar (glyc – glycosides i.e. sugars, haem -blood).  The lower the GI index, the slower the sugars it contains appear in the bloodstream, the higher the index, the faster the sugars appear in the blood.  Examples of GI indices in foods are:

HIGH:  White bread, white rice, potatoes, simple sugars, maltodextrin, glucose

MEDIUM:  Ice cream, banana, pitta bread, basmati rice, raisins, sucrose

LOW:  Beans, seeds, most vegetables, most sweet fruit, AND….. fructose

The sugars in this list make interesting reading.  White table sugar, aka sucrose, is actually medium GI, somewhat counter-intuitively.  And fructose (fruit sugar), a major component of high fructose corn syrup (HFCS), is actually low GI!  What’s that all about?  Even more surprising is that HFCS is used in many energy drinks in the US.  Why are the manufacturers using something that is slow to absorb is an interesting question.  I think the answer is twofold: firstly HFCS is cheap, secondly, it is about half and half fructose and…… glucose, which is high GI.

You might imagine that packing away a decent quantity of lower GI carbs in your feed might be a good idea, so that they are released slowly over a longer period of time.  I guess this is OK so long as there are not side effects. There is at least one manufacturer who markets just such a solution, known as superstarch from UCAN.  Superstarch is basically a more complex form of sugar polymer, in essence a low GI product, that releases glucose more slowly.  It is based on HMS, hydrothermally modified starch from corn.

Here are the marketing claims on the company’s website


They also conveniently provide a link to a journal article looking at the levels of (amongst other things) glucose and insulin in the blood of competitive cyclists over a 3 hour period of cycling at sub-maximal effort (measured as 70% of VO2peak).  One group were given maltodextrin feed, and the other Superstarch.  The trial was blinded, in that they didn’t know what they were getting, and a crossover study, in that they were invited to come back a week later and repeat, but this time they got the feed they DIDN’T get the first time.

Maltodextrin (open circles, HMS (closed circles)

Maltodextrin (open circles, HMS (closed circles)

Sure enough, you see a spike in glucose for maltodextrin in the first half hour after ingestion and the commencement of exercise.  This is accompanied by a spike in insulin that follows a similar profile.  No such spikes are observed for Superstarch.  ‘So far so good’, I hear you cry!  Well yes, I suppose.  I always ask myself at these moments the following question: ‘So what?’.  Why does this matter?  The line that UCAN offer is that insulin spikes harm the body’s ability to metabolise fat.  Maybe, but this effect only appears to be transient; for the remainder of the exercise period, both insulin and glucose map closely, before rising again once exercise ceases, and the glucose is no longer being consumed by the muscles.

Another proposed benefit I have heard is that the product allows you to feed less often.  Maybe again, maybe not.  The carb load you get from a gram of one will be very close to that you get from a gram of the other.  I can’t see that any magic happens to get round that fundamental, even if the profile of how that carb finds its way into your blood as useful glucose is modestly different.

Finally on this study, there is little discussion on the ‘So What’.  What is mentioned, however, is that there was no significant difference in performance after the monitoring period finished. “Upon completing the 150-min cycling bout, cyclists performed a time trial at 100% VO2peak to fatigue. Paired-samples t tests revealed that there was no difference between the HMS and MAL trials.”

I guess if people want to give this a try they can.  I know some distance swimmers who are doing precisely that, and one of them swears by it.  The unfortunate thing about Superstarch is that it doesn’t dissolve in the nice way the maltodextrin does, and has a fairly unpleasant mouthfeel.  It’s also not cheap.

Controlled experiments are always very difficult to conduct when it is just you as the subject of your own individual trial.  Confounding factors around performance, and the difficulty in obtaining objective data, cloud our ability to form judgements on what works best.  But at the end of the day, finding out what is best for us, while stress testing ourselves on long swims is the only way we have of coming up with the best thing for us.  I know that towards the end of my six hour Windermere swim in August, I was feeling a little peaky with all of the ribena-flavoured maltodextrin I chugged all of the way up the lake.  So I will make it less strong next time, or maybe drink less, or maybe both.

NOTE – I have no relationship, commercial or otherwise, with any vendors of products discussed today.

Not Getting Any Warmer Then?

Last night saw me back in the chilly waters of the Cam once again.

Helen, Bojan and I had a rematch with the river, and sure enough, there was only one winner again.

The water felt strangely ‘OK’ as I splash-dived into the dark river, only the glow of the city in the distance to light the entry.  The ‘OK-ness’ soon gave way to the cold, then the burn, then the general numbness as the extremities lost contact with the core.

We made it up past the aptly-named Deadman’s corner, where the Superfast Helen caught us up and kept going for a bit, while we turned back for home.

God it was cold as we got out back at the Riverbank.  Sure enough, it was a little colder than the Sunday night, with the water at 7.6C (45.7F), but still feeling lovely, rewarding, exhilarating, the slow, black, sloe-black creeping, fenny water.

(Apologies Dylan – for bastardising your masterpiece)

The Blooding of a Noob

I have a colleague Bojan at work who has been getting in to his swimming over the last 6 months, working his way up to 4 km pool swims, and improving his speed and technique, following a very similar path to the one I trod before him.

I had offered to take him to the river earlier on in the year, but he opted to concentrate on the pool work.  It was to my surprise, therefore, when he asked if he could come with me to the river last night for his first dip in the Cam.  I explained that it wasn’t especially warm now we are half way through November, but he was undaunted.  Scared yes, but undaunted, no.

Helen G and I discussed our approach, and agreed that we should be cautious in how we introduced a complete noob to sub 10C water, especially at night.  It is one thing if you work your way down gradually from higher temperatures, but another altogether if you go straight for ‘quite cold’ water.  I started swimming in the Cam in late summer when the water was still up at 17, and it has crept down since.

We agreed that Bojan would go in first, followed by me, with Helen remaining on the bank still in warm clothing.  We would swim upstream a short way, and back, a couple of times, and get out after < 10 minutes, to avoid an unpleasant rewarming.  Only once we were out and getting dressed would Helen go in for her own dip.

Bojan was a trooper.  I wanted him to go in first, to avoid the scenario where I got in, and then he ummed and aahed over his entry, leaving me to get nicely cold in the water.  There was no such issue though.  He went confidently down the steps up to his waist, then collapsed backwards into the inky water.  There was some very minor grunting and gritting of teeth while he got used to the feeling of the cold water, then I dived in and joined him.  We swam a little head up breaststroke for a while, before I asked him to do 4 strokes head in front crawl.  Then we did a little longer, then a little longer still.  I guess we went 50 m upstream, and he was feeling fine.  Despite that we opted to swim back to where we had got in.  While he was feeling OK, we didn’t want to risk him becoming ‘not OK’ a fair distance away from our exit point.  After getting back, we repeated the up and downstream routine, then got out up the steps of the Riverbank Club.

Back to the shed for a quick change and rewarm.  Rerwarming was OK last night, as we couldn’t have been in more than 10 minutes.  Helen took this photo before going in for her dip.

Post-Cam Glow

Post-Cam Glow

Note the big smiles.  It really was lovely last night: the river was fairly high after recent rain, but mirror smooth and velvety on the skin.  It had also not dropped in temperature as much as I had expected, holding up at 8.5C, but feeling warmer than the Ouse had at 8.7C a few days earlier.

Bojan didn’t even shiver, the sod.  You will see from the photo that he is a giant of a man, and has a good deal of natural core insulation.  He will be swimming the Channel one day, you mark my words.  I wonder how many Serbians have preceded him?  Answers on a postcard please…….

It’s November For Goodness Sake

I had never swum in properly cold water until recently.  The coldest I had ever experienced before this autumn was 13.3C in Jesus Green Lido in May this year.

Swims at a lower temperature have steadily become more the norm: 11C in the Cam on a couple of occasions, 12C in the Sea at Sandycove, 13C in Boston.

I was full of trepidation approaching the River Great Ouse at Coneygeare, St Neots on Sunday.  I had been away for a week in San Diego, enjoying some beautiful swimming in the Pacific at a balmy 16C,  so was concerned that no cold swimming for 10 days was not going to be enough to maintain any form of acclimatisation.

River Gt Ouse at Coneygeare

River Gt Ouse at Coneygeare

I met the Helens (Gibbs and Liddle) and Julie at 1 PM.  There was a distinct lack of enthusiasm from me and Julie, but the Helens jollied us along, and soon enough we were on the riverbank in togs, with the river in reasonable flow.

Passing dog walkers had asked incredulously what it was we were planning on doing.  ‘Swimming’ was the reply.  ‘Where?’, they rejoindered.  ‘In the river’.

In we got, in our different ways.  My favoured option is always the dive.  There is that short, delicious, period while airborne when you are still warm, but know you are about to become very cold.

Very cold was the truth.  The feeling wasn’t much different on splashdown, but the feeling on my skin as I swam upstream WAS different.  It was bordering on the painful, and the ice-cream headache persisted longer than I was used to.

After a 15 minute or so dip, I emerged tangerine-pink onto the riverbank with the others, and raced to the car to get dried off and changed before the shivers set in.  Once the layers were all on, I went back to the bank to check on the thermometer Helen (G) had dangled in the river.  8.7C!  Wow – over 2C lower than my previous low.

Roast dinner at a local pub was good though.

Back in the river Cam this week on Wednesday.  I have no idea what the temperature will be, but with the air temperature getting down close to freezing almost every night at the moment, I don’t imagine it will be  warmer than 8.7……

Good Morning Cove!

In San Diego with work this week.  Flew out of the UK on Monday afternoon, and after 11 hours in the air, found myself in the hotel at 7 PM.  A quick dinner with my boss who is also in town, and early to bed, for there was swimming to do in the morning……

I had already arranged to meet with Dan Simonelli for a 6 AM start time.  we splashed into the fairly calm waters of the cove, which felt gorgeous after the frigid water of the Cam which was the last open water I had been in.  The water was hovering around 61F today.  We did a lap of the Cove to Shores to Cove, before meeting Jim Fitzpatrick for another lap.  Jim is a great swimmer, and a bit of a legend, Triple Crown, and the first person to swim from Catalina to Orange County.

There was not a cloud in the sky today. As we swam the first lap, we watched the sun rise over the hills.  As we swam the second lap, the sun climbed the sky, and felt increasingly warm and comforting on the shoulders.  The third mile today was one of the most enjoyable I have experienced, with the three of us gliding through the gorgeous water seemingly effortlessly.  I was nicely warmed up by this point, and was totally digging the conditions and the companionship of 2 fine swimmers.

All in all, a wonderful start to the day: about 4 miles in the warm embrace of the Pacific Ocean.

I am hoping to come back in the New Year for a 6 hour swim with Dan.  I  hope to do my 6 hour channel qualifier.  Dan is registered for SCAR (40 miles over 4 days and 4 swims), so a cheeky 6 hours will do him no harm as well.