The main function of carbohydrates is to provide energy for the body. There are two types of carbohydrates – complex and simple. Complex carbohydrates are found in vegetables, whole grain bread and cereals, whereas simple carbohydrates are found in table sugar, honey, milk, white flour and fruits.

Complex carbohydrates are made up of a chemical structure with three or more sugars that link together to form a chain, while simple has one or two sugars. Due to their complex nature, they take longer to digest and do not raise blood sugar levels as quickly as the sugars in simple carbohydrates. Additionally, complex carbohydrates have more nutritional value as they are rich in fiber, vitamins and minerals.

References:

http://www.fitday.com/fitness-articles/nutrition/carbs/simple-vs-complex-carbohydrates.html

http://www.nlm.nih.gov/medlineplus/ency/article/002469.htm