Answer: Simply put, your body uses more carbohydrate for energy in a day than it uses protein to build muscle. Carbohydrates are pure energy foods that you continually use to keep your body alive and in motion. Protein is used primarily to maintain structures that already exist, hence very little is needed unless you are putting on pounds of muscle daily. Keep in mind that out of the 456 grams of weight in one pound of muscle, there are only about 120 grams of pure protein. The rest of the weight is fluid, glycogen and triglyceride. The only reason protein intake would be higher than carbohydrate is during severe and prolonged dieting.
Competitive or professional body builders have to achieve extremely low levels of body fat before a competition. To do this, calorie intake is continually lowered while exercise—including cardio respiratory, weight training and posing—is increased. (Competitive levels of body fat are generally unhealthy and impossible to maintain for prolonged periods.)
During negative energy balance (which is when one burns more calories than they consume) en route to competition-level body fat, protein requirements may dramatically increase.
Each component of this regime may have additive effects on protein requirements. Adaptations related to self-preservation, such as a higher hunger drive, reduced T3 and other hormonal levels (lowering metabolic rate slightly and increasing LBM loss) are probably highly active during this period, forcing a continued reduction in food intake to achieve the goal. However, to prevent the loss of existing muscle, protein intake cannot be lowered. In fact, protein intake may have to be increased in the final few weeks before competition.
During this period, the body is torn between the use of food components for energy expenditure and the support of muscle tissue. The athlete is forcing the body to achieve abnormally low levels of body fat for competition. When overall energy intake is significantly less than energy expenditure, the hormonal environment leads to the breakdown of muscle protein to be used for energy. When carbohydrate availability is limited, this effect is even more pronounced. Thus, it can be quite a challenge to balance these drastic measures with an appropriate mix of protein and carbohydrate intake. This illustrates the importance of using dietary supplements to prevent or reduce the loss of lean body mass while pursuing very low body fat levels.