Carbohydrates are starches and sugars obtained from food. After a meal, carbohydrates are broken down into smaller molecules as food travels through your digestive tract. Complex carbohydrates (found in starchy foods, such as pasta and potatoes) are long strings of sugar that require more digestion than simple sugars (such as sucrose in candy or table sugar).
Digestion begins in the mouth. There, a salivary enzyme called amylase breaks down carbohydrates into smaller molecules that pass through the esophagus and stomach and into the small intestine. Other enzymes from the pancreas and the intestine split the partially digested carbohydrates into simple sugar molecules small enough to be absorbed across the intestinal wall.
The absorbed glucose and other simple sugars then travel to the liver via the portal vein. Once there, glucose is released into the bloodstream based on how much your body needs for energy. Some of the unused glucose is stored in the liver and muscle tissue as glycogen for future energy needs and the rest is stored as triglycerides in adipose (fatty) tissue.
After the carbohydrates enter the bloodstream as glucose, the glucose triggers islet cells in the pancreas to release insulin. The insulin, in turn, allows glucose to move from the bloodstream into the cells in your body, where it is used for energy.
If you have type 1 diabetes, your pancreas produces little or no insulin, and instead of entering the cells, glucose remains in the bloodstream where it cannot be used for energy. If you have type 2 diabetes, your pancreas produces and releases insulin, but the cells are not sensitive enough to it and insufficient glucose enters the cells. The glucose that remains in the bloodstream signals the pancreas to produce even more insulin. Eventually, however, the pancreas is unable to produce enough insulin to overcome the cells' reduced responsiveness to insulin and treatment is needed.