Training & Nutrition - Insulin

I read that exercise that depletes muscle glycogen lowers insulin levels by allowing blood sugar to be stored into "empty" muscles, reducing the need for insulin to lower sugar levels. This is also part of the reason exercise is a crucial part of losing weight.

Also, insulin has been shown to constrict blood vessels, increasing the risk of heart attack and stroke.

Something else to worry about--I'm running out of room on my list.... :(

Insulin levels are naturally fairly constant in your bloodstream, if you are a healthly individual and not a type-1 diabetic. Exercise does a couple of things: (1) it increases your body's sensitivity to the insulin in your bloodstream, making the glycogenic pathway more efficient and (2) activates a secondary glycogenic pathway directly to your muscles. It doesn't actually increase the amount of insulin in your bloodstream.

On the other hand, by artificially increasing the level of insulin in your system, you can, in theory, increase the level of energy delivered to your muscles, hence the interest in insulin among pro racing dopers. The problem with that is that this can also cause your pancreas to shut down -- "gee, there's already too much insulin here, I'm not needed" -- which can turn a healthy person into a type-1 diabetic.

It can also create heart problems. This is somthing that type-1 diabetics [those who must inject insulin] have to worry about. It is not something that normal, healthy and active individuals who do not inject insulin have to worry about.

The article I read, by Dr. Gabe Mirkin ( www.drmirkin.com ) stated, "Regular exercise may help to prevent heart attacks by lowering insulin levels. When you eat, blood sugar levels rise and the higher they rise, the more insulin is released by your pancreas. You need insulin to keep blood sugar levels from rising too high, but it constricts arteries to cause heart attacks. Exercise uses up muscle sugar called glycogen so that when you eat, blood sugar goes into empty muscles. This keeps blood sugar levels from rising too high and bringing out extra insulin."

This article seems to be intended to promote exercise among sedentary people, for whom too much insulin could be a problem.

As I remember Biology class, Glycogen is a chemical agreggate of blood sugars (sort of, really a new chemical) created by the liver when there is excess sugar in the blood. This is stored in the liver - only in the liver.
There is no Glycogen in cells or blood vessels.

When you exercise, the liver reconverts the Glycogen to sugar and releases into the blood stream to the muscles to create ATP to 'run' the muscles.

When the liver exceeds its gycogen stores, it converts the glycogen to fat, and stores this in fat tissue.

When you exercise, first blood sugar is used - this requires no extra energy.
Then glyocogen is converted - this requires energy and makes you feel a bit shagged out.
To lose weight, you need to go to the next stage - 'burning fat'. This uses more energy, creates more heat and also creates a nitrogen overload - so you feel like absolute sh**.
This is why losing weight is so hard.

John, I would have to disagree about your statement that cells do not have any stored glycogen.

Glycogen is resident in muscle tissue and is available in limited quantities for "anaerobic" activity, such as sprinting. Restoring glycogen to the muscles is a key part of post ride muscle recovery.

Some quotes from Bicycling Medicine, by Arnie Baker, M.D.

"Moreover, the body's insulin response to sugar load during exercise is effectively turned off by the body's secretion of catecholamines (adrenaline and related compounds)."

"Insulin allows bloodstream sugars to be stored in the liver, muscles, and other areas as glycogen, or to be transported to adipose tissue and stored as fat."

"Without insulin, glucose stays in the bloodstream, and glycogen in [the] tissues is not made."