Fitness: Do protein supplements build muscle or fat?

Supplementing a tough lifting workout with a protein shake is common practice at the gym. Based on the premise that weight training breaks down the muscle and protein helps build it back up, these popular products promise to maximize the muscle-building effects of a good workout.
Containing a mix of high-quality proteins, amino acids, electrolytes and carbohydrates, most protein supplements come in powder form and are mixed with water or milk. Sold at gyms, pharmacies, grocery stores, online and