Carbohydrates, along with proteins and fats, are one of the three main food nutrients. They are the sugars and starches in foods that provide the main fuel for the body’s energy needs. They are also the substances that most affect a person’s glucose (blood sugar) levels. 

People with diabetes either cannot properly use or cannot produce insulin, a body hormone that prevents glucose levels from going too high or low. As a result, diabetic individuals must pay close attention to the amount and type of carbohydrates they consume as a way of keeping glucose in check.

About 90 percent of the carbohydrates a person consumes show up in the blood as glucose within two hours of being digested. Eating too many carbohydrates can cause hyperglycemia, but not eating enough can cause hypoglycemia or trigger ketosis, a potentially troublesome state for diabetic patients in which the body burns fats instead of glucose for energy.

There are two primary kinds of carbohydrates:

• Complex carbohydrates (starches). These include grain products, potatoes and vegetables that provide essential nutrition in the form of vitamins, minerals and fiber.
  
  
• Simple carbohydrates (sugars). These are found in fruit, milk products and sweets. Some simple carbohydrates – including fruits, milk and yogurt – contain valuable vitamins and minerals important to health. Other simple carbohydrates provide calories but little or no nutritional value. They can lead to undesired weight gain and obesity, a major risk factor for diabetes.

Different types of carbohydrates break down into glucose at various rates. Some peak rapidly and cause glucose levels to surge, and others are slower acting and cause a more gradual rise in blood glucose levels. A measurement system known as the glycemic index can help people with diabetes understand how various foods affect glucose levels. Methods including diabetic food exchange and carb counting can help patients track their consumption of carbohydrates.