"There's only one hard and fast rule in running: sometimes you have to run one hard and fast."








Tuesday, February 5, 2008

Sugar Seminar

I want to talk about long runs, but find I have to talk about sugars first.

Glucose, Fructose

There are onlt two sugars you need to know about, glucose and fructose. Table sugar (cane sugar, sucrose) gets converted in your body into one of each. Honey is slightly more than half fructose, the rest glucose. Most fruits contain just fructose (hence the name), the exceptions being dates, figs, canteloupe and watermelon. Starches are long chains of glucose; if the starches aren't digestible they're called fiber. Maltodextrin, found in many preparations for runners, is the simplest starch, made of three glucose units.

Glucose gets absorbed into the bloodstream very quickly. The glucose from starches takes a little longer (potato and corn starch almost immediately). What isn't needed by the body at once is converted to the storage starch glycogen and, when the body decides it has enough glycogen, what's left over is made into fat.

Fructose gets absorbed much more slowly and only 5% gets converted into glycogen under the best of conditions, so fat cells are adapted to using it when available.


Red blood cells use only glucose for fuel and the brain, under non-starvation or diabetic situations, uses only glucose. This is why the body needs to store glycogen in the liver (and to an extent, the kidneys). Muscles can use a number of different fuels, but store glycogen for anaerobic conditions. If there is no sugar available for the brain, the body starts breaking down proteins, which can be converted to a small degree into fuel.

What can go wrong

Eating a lot of carbohydrates quickly causes the blood sugar level to rise quickly. This leads to a large amount of insulin to be released to get the sugar level back to normal. This can then lead to too much sugar being removed from the blood for a while. This is an insulin reaction, or "sugar crash," which is very serious in diabetics and a major nuisance to runners, causing overwhelming tiredness. Visual disturbances, drunken behaviour and mood changes are common.

Muscles can be depleted of their glycogen. This is "hitting the wall." Once this happens in a run, there's no turning back the clock (though, if it happens to me in a 100 miler or 24 hour run, I'd be tempted to down every carb I can find and wait two hours, to see if it helps).

The liver can be depleted of it's glycogen, which is called "bonking." The physical characteristics are like the insulin reaction, but can be reversed by consuming sugars. Bicyclists are prone to this and not hitting the wall; apparently, it's a matter of bicycling using mostly large muscle groups whereas running uses a lot of little muscles for balancing and those run out of glycogen first.

Depletion runs

The reason this is important is that one can manipulate the amount of glycogen stored in the body and hence, run longer. This is done through carboloading (which I won't go innto here) and by intentionally running until one's muscles are depleted. Muscles that are regularly depleted of glycogen adapt by storing more.

5 comments:

Anonymous said...

You wrote:
This is an insulin reaction, or "sugar crash," which is very serious in diabetics and a major nuisance to runners,
I get this sometimes- actually I used to get it more and had a really hard time trying to figure out for a while what was happening. I felt like I was dying from hunger- there was no running through this feeling at all. I know now that it is from eating too much simple sugar stuff not from eating too little. It was horrible.
You metnioned on previous post that you had a diabetic reation even though you are not diabetic. Is this what you had happen? I really wouldn't think that because I thought this was only for pre-diabetics (like I am)who do not have insulin that works very well due to years of abuse.
Karen G

kurt decker said...

Yea I hate the "crash" feeling. I find the Hammer products works great since they are so anti-sugar.

phillip said...

Thank you for these teachings, Dr. 'Professor' Steve.
I'm applying for my 1 college credit right now for taking your course.
Maybe instructions like this will help me finish your Fab 5 Fifties Ultra Series runs . . . then I can bonk later, privately, in my car.
Phillip Gary Smith

SteveQ said...

Karen, I did say I had that sugar crash - my next training post will say I bonked pretty bad one day as well. What happened was that I put off running, waiting for the temperature to rise and got hungry. I wolfed down a lot of food just before running, which diverted blood supply from working muscles to digestion (problem 1). As my body was trying to lower the blood glucose level with insulin, exercising lowered the level even more (problem 2). There's a history of diabetes in my family, so I worry a bit. In my case, I think training has made me a little hypersensitive to sugar levels, rather than insensitive.

From some of the e-mails I've gotten, I should point out that I'm not anti-fructose. It's used as fuel and helps keep blood sugar levels even. It just isn't good for making glycogen.

Kurt, I never cared for Hammer products, though many swear by them. I make my own and am still tweaking recipes. I will say Hammer beats some of the other stuff out there. There's one replacement drink that both tastes bad and has nothing useful in it.

Phillip, have you read Karnaze's book, where he describes puking all over the company car after a race?

northwoods bryan said...

"...have you read Karnaze's book, where he describes puking all over the company car after a race?"

That part was hilarious. Still-recognizable cantaloupe chunks, I believe he mentioned.

"I wolfed down a lot of food just before running, which diverted blood supply from working muscles to digestion..."

I remember you mentioning this idea for training to eat on the run for a long ultra, but to do it in the freezing cold. I decided to try out your suggestion one night in December, when it was below zero, and I ate two big bowls of white chili and three sweet potato rolls and then immediately went out and ran six miles. I don't know if it helped train my ability to deploy blood to my legs and stomach at the same time, but it did cause a repeated sensation of almost puking up some of the chili.

This was a really interesting post though -- my maternal grandfather died at 52 from complications from adult-onset (i.e. type II) diabetes. It's too bad they didn't know then what we know now.