I would just like to comment on the "most proteins - hamburger, cheese and eggs" statement...
I don't think anyone who was seriously considering their health would think of a hamburger as a protein portion. Cheese IS high in fat, and relatively low in protein and also would never be considered a protein portion by bodybuilders/athletes. While eggs are high in fat, it is good fat and you can get eggs that have lots of healthy Omega 3s in. However, the protein in the eggs is found in the egg white, which has very little fat.
So "most proteins" ie, fish, chicken, cottage cheese, egg whites, lean pork, lean steak are actually low in fat, and higher in protein than say, a hamburger
While I agree that muscles grow by being used - acutally by being torn. The protein helps repair these micro tears in the muscles. This new tissue that is used to repair the muscles is built using ... duh duh duh... protein.
Extra protein will ONLY be converted into fat if you are taking in MORE CALORIES THAN YOU USE. If someone uses 2000kcals a day, but eats 1800kcals of protein they will not put on fat. They might have other health issues due to lack of vitamins and minerals and essential fatty acids, but the protein won't be converted to fat! Even if you do take in more calories than you use, out of the macronutrients (protein, fat and carbs) fat is the nutrient that is most easily stored as fat, then the carbs are stored then protein. The body finds it very hard to metabolise protein and to store it as fat.
Meg's study looks increadibly interesting and is from a reputable source. Read the article in full, it's very interesting.
Oh and another lovely reputable source on more of the science behind protein is "Sports Nutrition" by Anita Bean. She explains it so much more eloquently than I ever could!