The Basic Sugar the Body Uses As an Energy Source

Your body's muscles and nerves get working energy out of your blood in the form of glucose, a simple carbohydrate that circulates bonded to a percentage of red blood cells. Glucose can come into your system ready-made, your digestive system can make it out of other carbohydrates, or it can be recovered from storage in fatty, or adipose, tissue and your liver.

Digesting Sugars

• The most common sugar in food, including what's in your sugar bowl, is sucrose. Sucrose has a more complex chemical structure than glucose, and one that your body can't use as is. You also eat fructose, another simple sugar, particularly in fruit, and lactose in dairy products. Your food mixes with digestive enzymes and other chemicals in your mouth and passes down your esophagus and into your stomach, but the enzyme that breaks down sucrose doesn't get into the mix until the sugar is in your small intestine. The enzyme breaks sucrose into glucose and fructose, which are absorbed through the intestinal wall into your blood. Lactose has its own enzyme, lactase, also in the intestinal lining, as do various other sugars.

Digesting Starch

• The other main carbohydrate you eat, starch, converts to glucose in two steps. The first step starts in your mouth, with an enzyme in saliva. Down in the stomach, more chemicals from your pancreas turn the starch into the complex sugar maltose. Another enzyme in the lining of the small intestine breaks down maltose into glucose molecules that enter your bloodstream with the rest of the sugars.

On to the Liver

• Your liver has already participated in the digestive process by making bile to join the mix when food arrives. When sugars pass through the lining of the small intestine into the bloodstream, they go to your liver, which sorts out whether systems need energy now, or whether the sugars can be stored for later use. Sugars for storage are converted into triglyceride fat molecules and may be stashed in the liver itself or shipped off through the blood to adipose tissue --- where fat cells already exist to take them in.

Getting to Work

• If you're using your muscles in a workout, dancing, or strolling down the street, the liver answers chemical signals by shipping out sugar molecules attached to red blood cells. They'll have to go through the heart first, to use the arterial system. When one of these red blood cells gets to a nerve or muscle cell that's spent its available energy, circulating insulin, secreted by the pancreas, helps make the connection so the glucose can get into the cell.

Leftovers

• If you don't have enough insulin to get your circulating glucose into your cells, or you're not using insulin effectively, you have diabetes. This means that unused glucose, still riding on red blood cells, returns through the veins and continues circulating. It may damage muscle and nerve cells and the fine blood vessels where arteries become veins. The leftover sugar molecules may get stashed as fat in your liver, or they may be filtered out of the bloodstream by your kidneys and excreted in your urine, but that's another set of fine blood vessels that aren't built to deal with glucose, which is why diabetics are prone to kidney failure.

Hypoglycemia

• Your brain is the biggest user of glucose, and if you don't have enough coming in, such as when you've been asleep for several hours, it may call on your liver to convert some of the fats it has stored into glucose. In extreme cases, such as if you've overdone physical exertion without eating enough, your liver may need to raid proteins stored in your muscles to make glucose for your brain. This condition of extremely low blood sugar and ketosis can happen to diabetics even when they have glucose circulating, because of the imbalance of insulin to get the sugar into the cells.