http://www.everydayhealth.com/diet-nutrition/101/nutrition-basics/good-carbs-bad-carbs.aspx

Good vs. Bad Carbohydrates

Carbohydrates, often referred to as “carbs,” are your body's primary energy source, and they're a crucial part of any healthy diet. Carbs should never be avoided, but it is important to understand that not all carbs are alike.
Carbohydrates can be either simple (nicknamed "bad") or complex (nicknamed "good") based on their chemical makeup and what your body does with them. Complex carbohydrates, like whole grains and legumes, 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, according to Sandra Meyerowitz, MPH, RD, a nutritionist and owner of Nutrition Works in Louisville, Ky.

The Detail on Simple Carbohydrates

Simple carbohydrates are composed of simple-to-digest, basic sugars with little real value for your body. The higher in sugar and lower in fiber, the worse the carbohydrate is for you — remember those leading indicators when trying to figure out if a carbohydrate is good or bad.
Fruits and vegetables are actually simple carbohydrates — still composed of basic sugars, although they are drastically different from other foods in the category, like cookies and cakes. The fiber in fruits and vegetables changes the way that the body processes their sugars and slows down their digestion, making them a bit more like complex carbohydrates.
The most important simple carbohydrates to limit in your diet include:
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  • Soda
  • Candy
  • Artificial syrups
  • Sugar
  • White rice, white bread, and white pasta
  • Potatoes (which are technically a complex carb, but act more like simple carbs in the body)
  • Pastries and desserts
Meyerowitz says that you can enjoy simple carbohydrates on occasion, you just don't want them to be your primary sources of carbs. And within the simple carb category, there are better choices — a baked potato, white rice, and regular pasta — than others — chips, cakes, pies, and cookies.

The Detail on Complex Carbohydrates

Complex carbohydrates are considered "good" because of the longer series of sugars that make them up and 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.
Picking complex carbohydrates over simple carbohydrates is a matter of making some simple substitutions when it comes to your meals. "Have brown rice instead of white rice, have whole-wheat pasta instead of plain white pasta," says Meyerowitz.
To know if a packaged food is made of simple or complex carbohydrates, look at the label. "Read the box so you know what exactly you're getting. If the first ingredient is whole-wheat flour or whole-oat flower, 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 being 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 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 to 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, complex carbs fall into the low glycemic index category.
It is easy to find lists of food classified by their glycemic index. You can see the difference between the glycemic index of some simple and complex carbohydrates in these examples:
  • White rice, 64
  • Brown rice, 55
  • White spaghetti, 44
  • Whole wheat spaghetti, 37
  • Corn flakes, 81
  • 100 percent bran (whole grain) cereal, 38
To take this approach one step farther, you want to look at the glycemic load of a food. The glycemic load takes into account not only its glycemic index, but also the amount of carbohydrate in the food. A food can contain carbs that have a high glycemic index, but if there is only a tiny amount of that carb in the food, it won’t really have much of an impact. An example of a food with a high glycemic index but a low glycemic load is watermelon, which of course tastes sweet, but is mostly water.
The bottom line: Just be sensible about the carbs you choose. Skip low-nutrient dessert, consider the levels of sugar and fiber in carbs, and focus on healthy whole grains, fruits, and veggies to get the energy your body needs every day.

SOURCE:
http://www.everydayhealth.com/diet-nutrition/101/nutrition-basics/good-carbs-bad-carbs.aspx