Excess dietary protein is converted to muscle or expended as wasted energy or it is converted to glucose which can then be stored as fat. It doesn't just rot away in your intestine. Rather than ask us for proof, why not ask your friend for some proof? While he/she is gathering it for you (not bloody likely), read Dr. Eades' Protein Power and Mark's Primal Blueprint.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Highest squat: 167.5 x 2. Current Deadlift: 190 x 3