By Andrew M. Seaman (Reuters Health) – Diets high in protein from any source – animals or plants – may help keep muscles big and strong as people age, according to a new study. People with higher overall protein intake had higher muscle mass and stronger quadriceps, the muscle in front of the thigh, said lead author Kelsey Mangano of the University of Massachusetts in Lowell. Protein is known to protect bone density, muscle mass and strength, but it’s been unclear whether the protein must come from specific food sources, the researchers write in The American Journal of Clinical Nutrition.