Digestive Process

As we approach the time of year when you begin to build up mileage and or speed, the potential for the dreaded bonk, knock or whatever else you want to call it increases.  It can happen to anyone, even the best; ask Indurain or Armstrong, and it can most definitely happen to you.  It's something you have to experience at least the once.  Once you have, you'll make sure it never happens again. 

When the bonk hits it feels as though someone's just flicked the power switch to your body and mind.  It can be prevented so easily it's laughable.  Eat before you're hungry and drink before you're thirsty.  Read this factsheet to get an appreciation of what happens to your body when you eat, and why the previous sentence is so important.

8:00 am
We've woken up and already done most of the things necessary to prepare for our winter morning club run.  The night before we checked our tyres for cuts, brakes for operation and run through the gears lubing the chain for good measure.  We've done our drinks bottles, prepared our clothing stacking the pockets with energy bars and placed our clean, washed gloves and socks on the radiator; you can't see Museew doing it but it feels nice in the morning.  We've been the toilet (washed our hands!), cleaned our Oakleys and if you're Ian Hamon had a fag.

One of the most important things we can now do in preparation for our ride is to get a decent breakfast.  A bowl of cereal (preferably porridge due to its low glycemic index and preferably made with water), maybe some honey on toast and if it's cold out a cup of tea or coffee.  Although you may pay the price for this later on as we traverse the cold, windswept, toilet-less wasteland that is the north of the Island. 

One last check of the tyres, emergency toilet visit and we're ready to leave at 8:40 for the 9:00 am club run with plenty of time for a decent warm up and a leg stretch.

It's at this time that the 9:00 am club run leaves so you're warm up has been lost as everyone stands around in the cold waiting for the late comers to arrive.  They arrive late because they don't like waiting in the cold for ten minutes!  How ironic is that?

It's an hour into the ride and time to eat is running out.  Your breakfast should have taken care of the first hour and is being processed as we speak.  To ensure adequate energy supplies for later in the ride you slowly chew your energy bar.

As you chew the bar your teeth mash the bar to a pulp and the saliva in your mouth helps turns it to a dark pulpy, mushy gloop.  Your saliva's enzymes have already started to work on and break down the bar's complex carbohydrates before you've even swallowed it.

Once swallowed the bar is forced down your throat by muscle contractions that block your airways.  So you don't need me to tell you don't eat on a hill or when the chase is on.  Yet loads of people eat at the foot of a hill hoping the food will work quickly enough to get them up it.  Sadly it doesn't work like that. 

Once in the stomach the bar stimulates the production and release of acids and further enzymes to chemically break down the food.  The stomach produces three to four pints of fluid per day for this process.  Your stomach enzymes can only breakdown fats and proteins so the carbohydrates, processed elsewhere, are moved along and ignored. 

The process of exercise requires the body to use as many resources available to it that are not needed to maintain survival.  Digestion at this point is not deemed critical to survival so food is held in the stomach and digestion slows from its normal speed until resources become available. 

The stomach as we've seen, is flooded with fluids.  Each gram of carbohydrate requires three grams of water to process.  Water is now heading to your stomach which will cause dehydration and possible cramps if you don't drink enough fluids during your ride.   When digestion does occur the stomach goes into mild contractions to mix thoroughly it's gloopy, acidy, fluidy contents. 

By now the contents of the stomach are thoroughly mixed and will soon begin to separate out.  Fats rise to the top and carbs sink to the bottom.  The bottom of your stomach that is!

The mush has now almost been turned to liquid.  Yet even in this state it will not be ready for processing for a further quarter of an hour.  It's now possible to see the importance of energy drinks.  They bypass the early phases of munching and mixing and release their nutrients almost immediately on consumption.  Energy drinks moved on to the small intestine nearly twenty minutes ago.

Your body can run on its stored glycogen for around 90 minutes.  If you haven't eaten at all you are now well into the danger zone and could well blow at any minute.  For those that have eaten, the stomach, not a moment too soon, opens and begins to slowly pass its contents to the duodenum.  The pancreas adds enzymes to allow the digestion of carbs, and proteins while the gall bladder throws in some bile to help digest the fat.  It's been forty minutes since you first ate.

By now the carbs are beginning to be broken down in to glucose to be absorbed by the liver.  The proteins are beginning to take their form of amino acids and the fat starts to become fatty acids.  The body's absorption of these disparate nutrients can now begin.

The mush is heading for the small intestine, the first third of which concentrates on absorbing glucose for the liver.  Once the glucose reaches the liver it is used to manufacturer glycogen.  The glycogen is  stored in the liver itself and when needed transported to the muscles for immediate use or further storage.  Amino acids, fatty acids, vitamins and minerals go straight from the small intestine to the bloodstream.

The remnants of the bar are still in the small intestine, although most of its energy resources have now been used.

The training ride is almost over.  All of the bars glucose has been absorbed and most of the proteins partially processed.  Fat digestion and absorption has hardly begun.

The ride is over and now the "glycogen window of opportunity" is fully open.  Carbohydrates are the important food and should be eaten while the body is most receptive to them.  The energy bar is still being processed.  The protein de-constructed amino acids are just reaching the liver where they recombine to form plasma proteins and enter the blood stream.  The excess protein is metabolised for energy (a little too late) or turned to fat and stored for later use.

The remains of the bar now leave the small intestine and head for the large intestine.  Almost 90% of its nutrients have been stripped and it's on its way to its natural conclusion.  The large intestine reclaims the fluid used to aid digestion and returns it to whence it came. 

The Message
Eat early, eat little and eat often if you want to have a successful ride; and don't forget to drink.  Don't wait until you are hungry before you eat and don't wait until you are thirsty before you drink.  By then it's too late.  Your body can ride for around 90 minutes before its tanks start to run dry and it takes nearly 30 minutes to process what you've eaten.  So if you haven't eaten within the first hour it could be a long, slow, lonely ride home.