Glucose primarily comes from the carbohydrates in your diet, although some is also produced from fat and protein. Digestive enzymes break down the nutrient, transforming it into this vital energy source. But getting glucose into your cells isn't as easy as filling up your car with gas. For that, you need another component—insulin, a hormone produced by cells in the pancreas. Insulin acts as a key, binding to special receptors, or proteins, on cell surfaces and "unlocking" the cell to let glucose in.

As with most things in your body, blood sugar levels fluctuate, always aiming for a balance. They're at the high end when you've just eaten, sending a fresh supply of glucose out; and at the low end when you're hungry. If you've felt the dizziness, irritability and headache that comes on when you haven't eaten in a while, you know the feeling of low blood sugar, also called hypoglycemia.

While everyone experiences occasional episodes of low blood sugar, the problem is particularly prevalent and serious in people with diabetes who use insulin; too much insulin can send too much glucose out of the bloodstream, leading to plummeting blood sugar levels called hypoglycemia. Left unchecked, this could lead to coma or even death.

A far more common problem today, however, is hyperglycemia, or blood sugars that are too high. It's a common problem because so many of us are overweight, and being overweight increases the risk of insulin resistance. Insulin resistance occurs when you don't have enough insulin receptors on cells, or the insulin receptors don't work properly. Maybe they're not formed right, or maybe they're just stubborn and won't let glucose into the cells. That's why they're "resistant" to insulin. Initially your pancreas just pumps out more insulin to compensate and you maintain normal blood sugar levels. Over time, however, even that fails, and blood sugar levels rise. At this point, you're considered "glucose intolerant," or pre-diabetic, with a high risk of diabetes.

Be Blood Sugar Aware

How do you know if you're heading towards problems with your blood sugar? You get tested. The most common blood sugar tests include:

• The fasting plasma glucose (FPG) test, which measures blood sugar levels after you've fasted for a specified time.
• The HgbA1C test, which measures your average blood sugar level over weeks.
• The oral glucose tolerance test (OGTT), in which you drink a sugary liquid and then blood sugar levels are tested several times to see how well glucose moves into cells.

The American Diabetes Association recommends you take the same test twice, at different times, to confirm a diagnosis.

This information was produced with the support of an educational grant from Nutrition 21.