Good carbohydrates are high-fiber whole grains, vegetables and fruits that supply the body with a nutrient-rich, long-lasting energy source, while bad carbohydrates are low in nutrients and high in added sugars, according to the Centers for Disease Control and Prevention. Bad carbohydrates incorporate processed ingredients commonly found in refined grains, sugary beverages and "junk" food.
Carbohydrates are classified by the number of sugar compounds, or saccharides, they contain. Simple carbohydrates are sugars consisting of one or two saccharides, and complex carbohydrates are starches and fibers made up of a string of saccharides, according to Medical News Today. Sugars and starches are broken down to produce glucose and are absorbed into the bloodstream as blood sugar. Most naturally occurring sugars are digested at a manageable rate. Refined sugars are often absorbed so quickly that they cause rapid spikes in blood sugar, increasing the risk of developing serious health conditions such as diabetes.
Fiber is a plant-based nutrient that is not digested, but aids in the movement and absorption of other foods to prevent overeating and regulate blood sugar, the Mayo Clinic states. In refined foods, fiber content is often stripped away during processing, eliminating most of the food's nutritional value. In a balanced diet, carbohydrates should make up 45 to 65 percent of daily calorie intake with a heavy concentration of fiber. The CDC recommends avoiding consumption of high amounts of bad carbohydrates by checking nutrition labels for added sugars, such as fruit juice concentrate, dextrose, high-fructose corn syrup and lactose.