Considered the allies and enemies of many diabetics, glucose, fructose and sucrose are important carbohydrates. Although your tongue can't quite tell the difference between these simple sugars, they each play a different role in the body. People living with diabetes should pay especially close attention to glucose, which directly affects blood sugar levels. Here's what you should know about these three common carbohydrates.

Glucose

Glucose is the most the important simple sugar in our metabolism. It is the body's preferred energy source. Your body processes most of the carbohydrates you eat into glucose, whether to be used immediately for energy or to be stored in muscle cells or the liver as glycogen for later use. Glucose is measured in milligrams per deciliters and levels within the bloodstream naturally fluctuate throughout the day and night. Blood glucose generally becomes low between meals and during exercise.

The hormone insulin is responsible for keeping blood sugar at a healthy level. Insulin converts sugar, starches and other food into energy needed for daily life. Unlike fructose, high blood concentrations of glucose trigger the release of insulin.

Type 2 diabetes

In Type 2 diabetes, the most common form of diabetes, the body either does not make enough insulin or does not use insulin properly, which doctors call insulin resistance. In the early stages of Type 2 diabetes, the pancreas produces extra insulin to compensate, but over time it isn't able to sustain the overproduction. At this point, it becomes difficult for the body to keep blood glucose at normal levels.

Type 1 diabetes

People with Type 1 diabetes produce little or no insulin. Only about 5 percent of people with diabetes have this form of the disease, which is usually associated with children and young adults.

Hypoglycemia and hyperglycemia

When glucose drops too low, the condition is called hypoglycemia ("hypo" means "low;" "glycemia" refers to the presence of glucose in the bloodstream). Blood sugar below 70 mg/dL is considered low and poses a serious health risk. On the other side of the spectrum, hyperglycemia occurs when blood sugar is too high. Anything above 200 mg/dL is considered high.

Fructose

Fructose is another carbohydrate, but it does not result in the same spikes in blood sugar or insulin as glucose consumption. This carbohydrate is a natural sugar found in many fruits, vegetables and honey. It is the sweetest of the naturally occurring caloric sweeteners. Many people think of high fructose corn syrup when they hear fructose, but HFCS actually resembles sucrose more than fructose.

Fructose differs from other sugars because it has a separate metabolic pathway and is not the preferred energy source for the brain or muscles. It is only metabolized in the liver, depending on an enzyme called fructokinase to kick-start metabolism. The biggest difference between glucose and fructose: Fructose does not cause insulin to be released or stimulate the production of leptin, an important hormone for balancing energy levels.

Sucrose

Commonly called table sugar, sucrose comes from sugar cane or sugar beets. Fruits and vegetables also naturally contain sucrose. Chemically speaking, sucrose is made from both glucose and fructose units. When the sugar is consumed, an enzyme divides sucrose into its individual sugar units of glucose and fructose. Each sugar follows its normal metabolic route.

For more on diabetes and sugar:

Sugar or Fat — What's Worse?
Can Cinnamon Regulate Blood Sugar?
When Blood Sugars Rise Overnight