Your body requires blood sugar to function and you need to maintain steady levels to provide fuel for all of your bodily processes. Normal blood sugar levels range between 70 and 130mg/dl. After a meal, the blood sugar level should be higher, but no more than 180mg/dl. Sugar enters your blood stream by one of two mechanisms: through the food you eat or by breaking down the glycogen stores in your liver.
Dietary Sugar
Dietary sugar, or glucose, is also called a carbohydrate and it is present in most plant-based foods. Carbohydrates are made of chains of carbon and are classified as either simple, with a single chain of carbon molecules, or complex, with multiple carbon chains. Simple carbohydrates, such as those found in white potatoes and sweet foods such as donuts, are very similar to glucose and the body breaks them down quickly. Complex carbohydrates, such as those found in whole grains and leafy green vegetables, are more difficult to break down.
Glycogen Stores
Your body uses most of the sugar you eat for energy but stores some of it in your liver in the form of glycogen. You also store a small amount in your muscle tissue but those stores do not enter the bloodstream. Your body stores the glycogen for use when your blood sugar levels drop and you haven't eaten enough to raise your blood sugar levels.
Carbohydrate Digestion
The process of carbohydrate digestion starts in your mouth. Your saliva contains an enzyme called amylase that breaks down simple sugars, which you then absorb into the mucous membranes in your mouth and into your bloodstream. More complex carbohydrates travel to your stomach. Your body absorbs some of the carbohydrates into the bloodstream through your stomach lining and the rest travel to your small intestine where they are absorbed into your bloodstream through structures called villi.
Releasing Glycogen
Your blood sugar levels are lowest in the morning because you have gone for several hours without eating. If you do not eat right away, your body triggers the pancreas to release a chemical called glucagon. Glucagon stimulates the liver to release its glycogen and converts it to glucose in the bloodstream. Once you eat, your liver will convert some of the glucose back into glycogen. You will also tap into your glycogen stores during prolong periods of activity, such as running a marathon, if you do not replenish your blood sugar stores. This is why some athletes eat glucose-based energy supplements.
References
- "Principles of Anatomy and Physiology"; Gerard J. Tortora et al.; 2010
- Merck Manuals Online Medical Library; Carbohydrates, Proteins, and Fats; Margaret-Mary G. Wilson, M.D.; July 2008
- American Diabetes Association: Ask the Pharmacist Archive: What is Normal Non-Fasting Blood Sugar Level?
- Elmhurst College Virtual Chembook: Glycogen
