Are proteins a main fuel for cells?
They are a fuel for cells, but THE main fuel for cells is carbohydrates.
Not really. Their main function is in structural support for the cell. Carbohydrates are the main source of energy for the cell. Fats are the main storage material for the cell. A well rounded diet should contain 60 % carbs, 10% protein and 30 % fat. If the body does not get enough carbs it will tap into the fat storage, if there is no fat then the muscles are target next. At this point the person is in serious trouble and will eventually starve to death.
