A gain in body fat occurs from consuming a greater energy (calorie) intake than the body utilizes. It is a person’s habitual daily calorie intake overall rather than the consumption of a particular macronutrient (carbohydrate, protein or fat), that determines any alteration in body weight.
More to your point, usually, it’s the frequent consumption of foods that contain a lot of energy, whether it be in the form of sugars, fats or a combination of both, that underlies gains in body fat.
Of all the macro-nutrients, carbohydrates (complex and simple sugars) have the most profound impact on blood sugar and therefore, blood insulin levels. Insulin controls your ability to burn fat. This is why the carbohydrate choices you make each day can make or break your fat loss efforts during exercise training.
Carbohydrate (both simple and complex) is the fuel that powers intense exercise training, better knowledge about carbohydrate selection will enhance your performance in the gym as well as your efforts to shed fat. The key to a lean physique is knowing exactly what type of carbohydrates to eat and when to eat them.
As carb selection is so important, I’ve devoted an entire series of articles to this topic. In these articles, I’ve mapped out exactly the type of carbohydrates a bodybuilder needs to eat and when. Take a look at The Right Carbs for Building Muscle and Carbohydrtae Timing – How to Time Your Carbohydrate Intake For Maximum Muscle-Growth, Maximum Fat-Loss, and Maximum Workout Performance.