Fast carbohydrates are simple carbohydrates that are rapidly digested by the body and usually have little nutritional value. Slow carbohydrates have more complex structures, are usually high in fiber and nutritional content, and take longer for the body to digest, according to SFGate.
The glycemic index is a common way to describe the digestibility of carbohydrates. The index is determined for a carbohydrate source by measuring how fast it causes blood sugar to rise, reports SFGate. Fast carbohydrates have a higher score on the glycemic index, as they cause a rapid rise in blood sugar. Lower scores on the glycemic index describe a slower digesting carbohydrate.
Slow carbohydrates are usually recommended for their health benefits over fast carbohydrates. Overconsumption of fast carbohydrates can result in obesity, insulin resistance, diabetes, high blood pressure and cholesterol, and depression, reports SFGate.
Slow carbohydrates are characterized by their lack of processing, low levels of sugar, and high fiber content, adds SFGate. Common slow carbohydrates include oat bran, rolled or steel cut oats, most fruits and non-starch vegetables, stone ground whole wheat or pumpernickel breads, and barley. In addition, meats, nuts, eggs and seeds are low-glycemic foods, although not carbohydrate sources.
Fast carbohydrates are usually highly processed foods with added sugar and a low fiber content. Most baked goods, frozen foods and packaged foods are fast carbohydrates. Any food containing refined sugar or flour, such as white bread, crackers, or candy, is classified as a fast carbohydrate, according to SFGate.