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

Thursday, June 17, 2010

Running, biochemistry and homebrew supplies #1

It's been too long since I've written anything practical! I'm going to try to explain how the runner's body uses different sugars and then in a following post, the different types of sweeteners and sugars one can buy and what they contain. Parts of this will be very technical, but I'll try to minimize them. [They'll be bracketed like this.]

Exercise energetics in a nutshell: Resting muscles burn fat; burning fat requires oxygen. Exercising muscles prefer to burn sugar to burning fat and, when contracting faster than you can supply them with oxygen, burn only sugar. Running a lot of long slow miles burns fat (and this is often the only reason a person will run), but unless one ingests fewer calories than are burned, the fat gets replaced. Training by running at a faster pace causes the body to adapt by becoming more efficient and thus burning more fat and less sugar at a given pace. Training at an exhaustingly fast pace causes the body to adapt by storing more sugar and by shifting some of the energetic needs of the muscles to the liver.


The body has an absolute requirement for this sugar; your red blood cells can use nothing else and your brain has to have it as well. If you don't have any in your system, your body will make it out of whatever is available. It's the basic currency of sugars in the human body. A typical 2000 calorie diet will contain about 200 grams of glucose.

If you ingest a large amount of glucose, the sugar will have three different fates. First, whatever immediate energy needs the body has will be taken care of by burning this sugar. Second, some of it will be stored in the form of glycogen in muscles and liver for future use. Third, whatever is left over will be turned into fat; this fat can not be turned back into sugar, so one needs to keep supplying the body with a source of glucose.


The same typical 2000 calorie diet will contain about 100 grams of the sugar fructose. This sugar is utilized differently than glucose. Muscles do not have the required machinery to use fructose for energy, so it has to be used elsewhere or converted into glucose elsewhere before the muscles can use it.

In the liver (under normal conditions), fructose cannot be easily turned into glucose. [It gets converted to fructose-1-phosphate, then to glyceraldehyde and dihydroxyacetone phosphate. The glyceraldehyde gets phosphorylated and can then recombine with the dihydroxyacetone phosphate to form fructose 1,6 bisphosphate, which can in turn become: fructose-6-phosphate, glucose-6-phosphate, glucose-1-phosphate, UDP-glucose, then glycogen. Whew!] Instead, it gets broken into smaller parts and used for energy. These smaller parts can be exported to muscle cells for use there.

The majority of fructose ends up going directly to fat cells, which cannot make glucose or glycogen out of it, either. It is used to make more fat (that's what fat cells do). This fat can then be exported and used by muscles, if needed.

Minor sugars

There are dozens of different sugars, but most occur in very tiny quantities. There are two that occur in large enough quantities to warrant mention: galactose and ribose. These sugars are available in forms one can buy, so it's worth looking to see if there's a biochemical "shortcut" one can exploit for energy needs.

Galactose can be converted into glucose in the liver and then get exported or turned into glycogen. The only dietary source of this sugar comes from the breakdown of another sugar, lactose, found in milk. Adults have a widely varying amount of the enzyme used for breaking lactose into galactose and glucose; that which cannot be broken down goes into the intestine, where bacteria feed off of it (causing gas) or it gets excreted (often as diarrhea).

Ribose is used as part of DNA in every cell, so it's everywhere, but in very small quantities, compared to glucose and fructose. The amount of ribose one ingests is negligible, though it has recently become available as a dietary supplement, so it is theoretically possible one could use it for energy. If one were to ingest a large amount of ribose, the body has a system (the pentose phosphate shunt) that allows it to be used. It's very complicated.

[ Under aerobic situations, 3 ribose-5-phosphates become 2 fructose-6-phosphates and 2 glyceraldehyde-3-phosphates. Then, 4 fructose-6-phosphates plus 2 glyceraldehyde-3-phosphates plus water become 5 glucose-6-phosphates and one free phosphate. Then glucose-6-phosphate plus 2 NADP plus water become ribose-5-phosphate, 2 NADPH, 2 hydrogen atoms and carbon dioxide. The sum total of these reactions is glucose becoming carbon dioxide.

Under anaerobic conditions, ribose becomes ribose-5-phosphate, which becomes fructose-6-phosphate and glyceraldehyde-3-phosphate. Fructose -6-phosphate becomes fructose 1,6-bisphosphate, which then splits into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. Dihydroxyacetone phosphate becomes glyceraldehyde 3-phosphate. All this glyceraldehyde 3-phosphate gets turned into pyruvate, which can be used by muscles to make lactate, which then gets shuttled back to the liver, which can reuse it to make more glucose.]
Not that you needed to know that! Trust me, there will be useful information forthcoming.


joyRuN said...

Was this to avoid posting a pic of your canker sore?

All I wanted to know was: run slow, burn fat. Got it!

Glaven Q. Heisenberg said...

What you say here is true for most runners.

But my body? It turns everything I ingest into penis cells.

This is why people always say, "Glaven's a Big Dick!" (I assume "Glaven's" is short for "Glaven has".)

I applaud you for not letting joyRuN know that because if she did how could she ever be happy with her little "run slow, burn fat" quote-unquote "knowledge"?

Pfffttt! Talk about a lousy second prize! Let her go on thinking it's First Prize!

RBR said...

...which can be used by muscles to make lactate, which then gets shuttled back to the liver, which can reuse it to make more glucose.

Ok, do not laugh at me. I am not Sea Legs Girl or you, just a lowly high school teacher, but I have a couple of questions. (Boy, are you going to be sorry you brought his up)

In my understanding, only about 20% of the lactate produced ends up this way as triggered by increased ATP levels (and other gluconeogenic stimulators like cAMP cascade, epinephrine,etc..) The remaining 80% of the lactate is oxidized by type 1 skeletal muscle cells and cardiac cells (and I am sure some others to a lesser extent. I can not find my Stryer text to save my damn life)

My question pertains to this 80% that ends up metabolized for energy and exogenous versus endogenous lactate.

1. Is this only pertinent to type 1 skeletal muscle cells and cardiac tissue? Meaning, do other cells types release all produced lactate to the bloodstream to be taken up by type 1 skeletal muscle cells (I also hear there is evidence that these cells may also have gluconegenic capabilities, thoughts?) and cardiac cells?

2. Mitochondrial lactate dehydrogenase is found in relatively high concentration in skeletal and cardiac cells, but is it absent in other cell types?

3. Is it only mitochondrial LDH that can convert lactate to pyruvate?

I know this is not where you are going with all this, and feel free to tell me to buzz off.

Glaven Q. Heisenberg said...

I have an answer for RBR!



SteveQ said...

@RBR - Geez, I get sloppy for a second [yeah, G. "sloppy seconds"] and you jump all over it. I'm going to need some time to answer those questions, Ms. Smartypants.