It means that you should eat more complex carbohydrates like cereals and grains in order to keep your body from breaking down protein for energy. Eating excessive protein, like most Americans do, is bad for your kidneys, liver, bones, cardiovascular system, and promotes vitamin and mineral deficiencies. It causes dehydration and is linked to osteoporosis, hypertension, and some forms of cancer. Too much protein is a bad thing. Proteins have nitrogen in them and their breakdown in the liver creates ammonia.
Ammonia is toxic.
It is a poison to every cell in your body, especially your brain cells. So you pee it out. This is partly the point in going pee, to save your body from ammonia. Excessive protein intake can also make your blood acidic. To resist this change your body forces water out of your blood and pulls calcium from your bones into it.