What Are Slow Carbs & Fast Carbs?

Carbohydrates are categorized as "slow" or "fast", depending on how quickly they raise blood sugar levels. Carbohydrates are absorbed into the bloodstream as glucose, or sugar. As glucose levels rise, insulin is released to convert the excess glucose into energy. The glycemic index indicates how quickly a food will raise blood sugar. Slow carbs are low on the glycemic index, and fast carbs are high on it.

Slow Carbs

Eggs and dairy products are part of a slow-carb diet.

Slow carbs are absorbed and converted into glucose at a steady rate. They raise blood sugar levels slowly, which helps regulate hunger and cravings. Slow carbs also allow blood sugar levels to remain normal, allowing for regulated energy supplies. Slow carbs come from foods that are low on the glycemic index, such as oatmeal, whole grains, beans, brown rice and lentils. Many slow carbs are also good sources of fiber and protein.

Fast Carbs

Fast carbs contain fewer nutrients than slow carbs.

Because fast carbohydrates are converted into glucose quickly, they cause a sudden burst of energy because of high insulin levels. The faster a carb is absorbed as glucose and converted into energy, the faster that energy is exhausted and needs to be replaced. Therefore, fast carbs cause blood sugar levels to spike then crash, which leads to hunger and cravings. Fast carbs can be found in pasta, white breads, fruits, white rice and potatoes.

Glycemic Index

The glycemic index was developed to assign numbers to foods based on their sugar content. Glucose is assigned the number 100, and all other foods' sugar contents reflect their glycemic index relative to glucose. Foods with a high glucose content, such as doughnuts, have a glycemic index of 70 or more. Foods with a low glucose content, such as whole grains or some fruits (which contain fructose, a different sugar), have glycemic indices of 55 or less.

Guidelines

Choose whole-grain bread instead of white bread.

Eating whole-grain foods and foods low on the glycemic index will help regulate blood sugar levels. During exercise, it might be beneficial to consume a small amount of high-glycemic food for a quick energy boost. Fruit is a healthy source of high-glycemic carbohydrates. Vegetables low on the glycemic index should be eaten daily, as they help stabilize blood sugar levels.