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don't skip your breakfast!


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Sources of Blood Glucose.

The first line of defense against a fall in blood glucose is the liver's glycogen reserve.  This polysaccharide can be rapidly split into glucose units which are then transported to the blood.  Indeed, this is the only major function of liver glycogen.  It is not utilized by the liver to support its own requirements for energy. 


Look at the curve to the left.  This gives an picture of the normal fluctuations in liver glycogen levels throughout the day.  (Note that the curve starts and ends at 8:00 AM). 


Liver glycogen levels fall dramatically during the night.  We wake up with little or no glycogen reserves.  The day should begin with a breakfast that includes carbohydrates. The glucose from these replaces the glycogen that is used while we sleep.  Liver glycogen falls thereafter, supporting blood glucose levels during the morning's activities.  A new increase in hepatic glycogen follows lunch, and a major climb is seen after a "good dinner" and an evening snack.  Then comes the long dark night and glycogen levels fall once more to rather low levels.




What if you do not "listen to Mom" and skip breakfast?  Well, your blood glucose will probably be just as stable as after a good meal, but the mechanism for this will be quite different.  Instead of a hormone balance dominated by insulin and synthetic processes, skipping breakfast forces the body to call forward the stress hormones glucagon, adrenaline and growth hormone.    These rearrange metabolism such that lactate and amino acids are converted by the liver to glucose, so-called gluconeogenesis.  We see that gluconeogenesis is quite active after about 10-12 hours after the last meal.  This may be a useful solution to keep blood sugar stable, but the stress hormone response does not lead to an ideal  setting for learning or contemplative work. 

Gluconeogenesis can provide enough glucose for moderate energy utilization for some weeks, using amino acids derived from muscles as substrate.





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