Saturday, October 30, 2010

Metabolism Part 2: Exercise and Metabolism

This is Part II in a series about the science of metabolism. I am not an exercise scientist or registered dietitian, I am merely a biochemist with an interest in the way our bodies work. Consult your doctor before starting any crazy diet or exercise plans based on my posts!

If you've been reading my blog, you know I like to exercise. I like to run, bike, swim, lift, and generally be active in my life.

It makes me happy and balanced. It also allows me to eat and experience a wide variety of foods. The way my body uses food and turns it into energy is called metabolism. If you missed the basics, you can find them here.

So, I've been trying to think of how to tell you about the ways exercise effects your metabolism, and I think I want to highlight the ways exercise effects specific parts of you, and then talk about how they go together.

These parts are:

1) Your Brain
2) Your Muscles
3) Your Gastrointestinal Tract
4) Your Future!
(That one's for you, nearly cousin-in-law!)

When we talked about carbohydrates, we learned that glucose is the only fuel your BRAIN can use and that glucose is stored in your liver (~10%) and muscles (~1%).

Your MUSCLES also prefer to use glucose, and while other sugars (like fructose and galactose) can be converted to glucose or directly into energy, it isn't done efficiently while exercising. So, when you run out of MUSCLE glucose (which occurs rather quickly - 10 minutes during intense exercise!) your body starts mobilizing glucose from your liver.

Glucose from your liver circulates in your blood and fuels your BRAIN and your MUSCLES. But, if you don't keep fueling yourself, you can't efficiently convert fats or proteins into glucose while exercising, so you will 'hit the wall'. 'Hitting the wall' happens after 60-90 minutes of intense exercise and it signals an empty tank. You don't have enough glucose circulating in your blood to fuel your brain. If you don't fuel yourself, you can black out.

You can, over time, increase your glucose stores mildly,

A question I often get at this point is how people who are panicking or running for their lives can keep going without enough fuel. Adrenaline is a signalling chemical that does amazing things for your body. It takes away mental blocks on abilities and gives you the feeling that you can do anything. Adrenaline allows you to run through the 'yellow light' of 'hitting the wall' and keep going until you hit the 'red light' of absolutely empty. It does this by signalling to your body to increase blood flow and clearance, which increases nutrient and oxygen transport to your muscles. It also is a neurotransmitter, which means it signals in your brain

Do you get an upset stomach when you exercise?  Hey, it happens to everyone. When you are vigorously exercising, your body is more interested in fueling your BRAIN and your MUSCLES than digesting. It is also trying to suck all of the water, electrolytes, and glucose out of your intestines, and you become very sensitive to dehydration during this process. As a result, GASTROINTESTINAL problems often occur.

STOMACH cramps can occur when you've had too much to eat before you exercise, or when you eat too complex of foods. If your body is having difficultly digesting, such as with fiber and lots of protein, you may get stomach cramps. Simple carbohydrates are the best way to fuel your body immediately prior or during exercise.

Some people can eat whole foods during exercise - fruits, crackers, etc. I can't. I have a very sensitive STOMACH. For me, I have to have simple sugars, primarily glucose, to fuel long exercise sessions. I prefer gatorade or gu gels, which are easily absorbed once they hit my GASTROINTESTINAL (i.e. stomach and intestinal) tract.

You may have giggled when I said exercise effects your future, but it does. Exercise has been linked to a longer and healthier life. Making time for a small amount of exercise, even 30 minutes 3-4 days per week has been shown to have immense health benefits. Get moving! It'll be good for you, your family, and your FUTURE!

I need to get going now. Sorry for the very wordy post. I wanted to put links in, but the internet is timing out. So, if you want a reputable source for anything I've posted today, please let me know. Leave a comment with the statement you'd like cited and I'll get you something immediately.

Happy Halloween! 

1 comment: