Carbohydrates are an important part of a healthy diet, but there's much discussion about “good” and “bad” carbohydrates. So how do you know which is which? The answer is both simple — and complex.

Carbohydrates, often referred to as just “carbs,” are your body's primary energy source, and are a crucial part of any healthy diet. They should never be avoided, but it is important to understand that not all carbs are alike.

Breaking It Down

The three main kinds of carbohydrates are sugars, starches, and fiber. They're called “simple” or “complex” based on their chemical makeup and what your body does with them, but since many foods contain one or more types of carbohydrates, it can still be tricky to understand what’s healthy for you and what’s not.

Simple carbohydrates are composed of easy-to-digest, basic sugars, which can be an important source of energy. Some of these sugars are naturally occurring, in fruits and in milk, while refined or processed sugars are often added to candies, baked goods, and soda. When trying to figure out if a source of carbohydrates is good or bad, remember this: The higher in sugar it is, and the lower in fiber, vitamins, and minerals, the worse the food is for you.

Complex carbohydrates, found in whole grains, legumes, and starchy vegetables, contain longer chains of sugar molecules; these usually take more time for the body to break down and use. This, in turn, provides you with a more even amount of energy, says Sandra Meyerowitz, MPH, RD, nutritionist and owner of Nutrition Works in Louisville, Kentucky.

The Details on Simple Carbohydrates

Simple carbohydrates aren’t necessarily good or bad — it depends on the food you’re getting them from. For instance, fruits and vegetables are excellent sources of essential vitamins and minerals necessary for good health, and naturally contain simple carbohydrates composed of basic sugars. But fruits and vegetables are drastically different from other foods in the “simple” carbohydrate category, like cookies and cakes with added refined sugars. The fiber in fruits and vegetables changes the way the body processes their sugars and slows down their digestion, making them a bit more like complex carbohydrates.

Simple carbohydrates to limit in your diet include those found in:

  • Soda
  • Candy
  • Cookies
  • Pastries and desserts
  • Sweetened beverages, such as lemonade or iced tea
  • Energy drinks
  • Ice cream

Meyerowitz says that you can enjoy simple carbohydrates on occasion, you just don't want them to be your primary sources of carbs.

The Details on Complex Carbohydrates

Complex carbohydrates are considered "good" because of the longer series of sugars that make them up, which take the body more time to break down. They generally have a lower glycemic load, which means that you will get lower amounts of sugars released at a more consistent rate — instead of peaks and valleys — to keep you going throughout the day.

Foods with complex carbohydrates also typically have more vitamins, fiber, and minerals than foods containing more simple ones. Whole grains, for instance, provide more nutrients than processed grains.

It’s important to scan ingredient labels for foods like breads and pastas, looking for whole grains and fewer sources of added sugar. "Read the box so you know what exactly you're getting. If the first ingredient is whole-wheat flour or whole-oat flour, it's likely going to be a complex carbohydrate,” says Meyerowitz. "And if there's fiber there, it's probably more complex in nature."

The Glycemic Load Factor

Describing carbs as either simple or complex is one way to classify them, but nutritionists and dietitians now use another concept to guide people in making decisions about the carbs they choose to eat.

The glycemic index (GI) of a food basically tells you how quickly and how high your blood sugar will rise after eating the carbohydrate contained in that food, as compared with eating pure sugar. Lower glycemic index foods are healthier for your body, and you will tend to feel full longer after eating them. Most, but not all, foods containing complex carbs fall into the low glycemic index category. It is easy to find lists of food classified by their glycemic index.

To take this approach one step further, you want to look at the glycemic load (GL) of a food. The glycemic load factors into account both glycemic index and how much carbohydrate is in the food. To determine glycemic load, you multiply a food's glycemic index number by the amount of carbohydrate the food contains per serving, and divide by 100. A low GL is 10 or less; medium is 11 to 19; and 20 or greater is considered high. For instance, a plain bagel has a GI of 72 and GL of 25, while whole-wheat bread has a GI of 69 and GL of 9.

Even if a food contains carbs that have a high glycemic index number, if the amount of carbohydrate is low then it won’t have as much of an impact. A good example is watermelon, which has a GI of 80 but a GL of only 5. It tastes sweet, but it’s mostly water.

The bottom line: Just be sensible about the carbs you choose. Skip low-nutrient desserts, consider the levels of sugar and fiber, and focus on healthy whole grains, fruits, and veggies to get the energy your body needs every day.