It's nearly impossible to design a diet with a variety of whole foods that is deficient in protein. If you consume enough calories to meet your energy needs, you'll get more than enough protein. If a little protein is good, a lot is better. In developed countries, too much protein is a much bigger health threat than too little. Excess protein leads to kidney overload and mineral deficiency diseases, such as osteoporosis.
Vegetarianism is too complicated.
To get quality protein, one must carefully mix and match foods. Research has proven this unnecessary. Bananas have complete protein. Check any official food chart listing for amino acid content. Dairy products are necessary for calcium.