Wednesday, September 13, 2017

What Happens When We Fast?

When we fast (sleep for 8 hours), our body needs to continue supplying fuel to our cells. Glycogen in our liver is broken down into glucose and triglycerides in our adipose tissue are broken down into fatty acids. Both derivatives are released into our blood to flow into our cells. Once inside our cells, they are broken down to Acetyl CoA and enter the Krebs cycle to be converted into energy. 

After several hours of fasting, our liver glycogen is depleted and our blood glucose begins to drop. Our brains and nerves prefer energy in the form of glucose, but our red blood cells absolutely depend on it. Normally, restocking our glucose is not a problem since our hunger hormone, ghrelin, has already been released from our stomach to stimulate our appetite.

But, what happens if we don't eat breakfast right away? Cotisol is responsible for maintaining blood glucose levels by breaking down fat and muscle. Glucose for our blood is dervied from the glycerol portion of our triglycerides and our amino acids from our muscles. Fuel for our cells comes from the fatty acids of our triglycerides as well as the amino acids from our muscles. This is all fine for a little while, but if the fast continues for too long, our body starts to convert Acetyl CoA fragments (acquired from fatty acids) into keytones to provide the glucose needed. 

Sometimes ketone bodies have an acid group attached, and If we have too many of those floating around, our blood pH drops. The acidity denatures proteins, leaving them unable to function. This is bad news because our muscles start shrinking and our metabolism slows. We know we are at this point in a fasted state because we emit an odor similar to nail polish.

Though it's probably best to fast only when we sleep, it can be done safely for a short period of time to jump start a weight loss program or simply regain control of our eating. Having the knowledge about how the process works will help us preserve our muscle mass.

After intermittent fasting and an 8-mile hike (waiting for my pasta w/ Fish of the Day)

Whitney | Rolfes. "Understanding Nutrition." Cengage Learning 2011.
Talbott, Shawn. "The Cortisol Connection." Hunter House, Inc. 2007.

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