What Are Fast & Slow Carbohydrates?

Fast and slow, when referencing carbohydrates, refers to the speed at which carbs get digested and converted to blood sugar. This is important for many reasons. For example, slowly and rapidly digested carbohydrates have different effects on how your insulin responds. That has ramifications for your appetite and weight, as well as your body's control over blood lipids, like triglycerides. Broadly speaking, slow carbohydrates are more desirable for good health.

Cast of Carbohydrates

Carbohydrates are officially categorized as simple and complex. The basic building block of all carbs is the simple sugar molecule, which combines carbon, hydrogen and oxygen. Simple carbs are relatively simple chains of sugar molecules, while complex carbohydrates are more intricate spiraled, coiled and branched sugar molecules --- and there are a lot more of them than in simple carbohydrates.

Fast Carbohydrates

When you digest carbohydrates, they get broken back down into simpler sugars in your digestive tract and turned into blood glucose, which provides energy for your cells. Because of their chemical makeup, simpler carbs are easier to break down so they digest "fast" and are quickly absorbed for the purpose of creating blood sugar and energy. Examples of quick-burning carbs include refined grain products, like white bread, corn flakes, candies, and other highly processed foods, along with honey and also some fruits.

Slow Carbohydrates

Complex carbs, because of their complicated and nuanced chemical structure, tend to take somewhat longer to break down into blood sugar. They are said to be slow carbohydrates for that reason. Examples of complex carbs include whole-grain products; beans, lentils and peas; sweet potatoes; bran; brown rice, bulgur and barley; and whole oats.

Why Carb Speed Is Important

When your body creates blood sugar from carbohydrates, your pancreas secretes a hormone called insulin. The job of insulin is to shuttle blood sugar into your cells, but insulin is a dynamic substance with a host of other functions you need to be mindful of. So, each time you eat fast carbs, you are potentially spiking your blood sugar and sending your insulin levels on virtual roller coaster ride. David Ludwig, a pediatric endocrinologist, told Harvard Medical School's "Focus" newsletter that rapid changes in blood sugar set insulin off to make your body store more fat. It increases your hunger and the constant back-and-forth of blood sugar can tax your pancreas. This sets the stage for insulin resistance and diabetes.

Which Carbs to Eat

The Dietary Guidelines for Americans 2010 recommends that most healthy people eat between 45 percent and 65 percent of their daily calories as carbohydrates, preferably from complex carbohydrate sources, as these come with a healthy mix of vitamins and minerals. In a pinch, fast carbs from sources like grapes and other sweet, juicy fruits provide a quick dose of energy that keep your body humming. Natural, unprocessed fast carbs also provide important nutrients. Too often, however, Americans consume fast-burning carbs in the form of refined flour products, like pizza, pastries and desserts and sugary drinks. In addition to provoking weight gain and abdominal fat, they can also cause intense cravings because they lack healthy nutrients and they can promote a buildup of triglycerides, which can start you on a path toward fatty liver and heart disease.