Carbohydrates are one of the main macronutrients that provide the body with energy (4 calories per gram). Though fat and protein can also be a source of energy for the body, carbs are the body's main source without which, peak performance will be unattainable.
All carbohydrates are made up of sugar molecules. The characteristics of the carbohydrate depends on how many sugar molecules are linked together. Carbs can be split up into two main categories: simple and complex.
Simple vs. Complex Carbs
The more sugar molecules a carbohydrate contains, the more 'complex' it becomes. Inversely, the less sugar molecules, the 'simpler' it is. The complexity of a carbohydrate impacts the digestion and absorption time which in turn dictates how the body reacts to it.
Simple carbs are usually a few sugar molecules linked together. Because simple carbs are small, they are digested and absorbed very quickly. This property makes them great to take before, during and after a workout because they'll give you a quick boost of energy.
Complex carbs can contain hundreds or even thousands of sugar molecules which takes the body a lot longer to digest and absorb. This makes them a bad option before, during or after a workout because they won't give you the energy you need right away. They are however a great option for the rest of the day. Replacing simple with complex carbs will help you: avoid sugar crashes, improve your body fat composition and even lose weight.
Because simple carbs are digested very quickly, your body receives a huge amount of energy in a short period of time. If you don't burn that energy off quickly, it will be store those excess calories as fat for later use. You should minimize your intake of simple carbs throughout the day with the exception of working out.
Complex carbs are digested slower and will give you a more stable energy release meaning you won't have to burn as much energy to prevent fat storage. You should replace your intake of simple with complex carbs throughout the day.
Simple carbs are found in sugary foods including but not limited to sodas, fruit juices, white bread, doughnuts, muffins, cookies and other pastries. Complex carbs can be found in 100% whole wheat bread/pasta, brown rice, vegetables, legumes and beans.
Low Carb Diets
Low carbohydrate diets have become popular in the last few years in part because they seem to help you lose weight. The reason that low carb diets "work" is because they cause you to eat less. When you take in less calories, you will lose weight. Simply losing weight however, doesn't necessarily mean you're getting healthier. There are good and bad ways to lose weight and low carb diets are generally unhealthy. A better option is cutting bad calories such as trans/saturated fats and simple carbs.
The Bottom Line
Carbohydrates are the body's main source of energy and as such, can't be cut out of the diet. Foods containing complex carbs are also rich in nutrients such as vitamins, minerals, fiber and antioxidants without which the body can't function properly. Carbs are an essential part of a healthy lifestyle regardless of your weight goals.