Protein Sources

Protein is necessary for health. We need protein for growth (especially important for children, teens, and pregnant women), tissue repair, immune function, making essential hormones and enzymes, and preserving lean muscle mass

According to the Dietary Reference Intakes published by the USDA, 10% - 35% of calories should come from protein.

I have realized recently that many people get too much protein in their diet or they hardly get any at all.  Few get the recommended amount. 

Too much protein isn't good because it causes your kidneys to work harder to metabolize it.  If you increase your calories and your protein, it will be stored as fat.  If you keep your calories the same and increase your protein, you will probably be cutting carbohydrates too low and start feeling crummy. 

Eating too little protein can lead to thinning hair, general weakness, muscle soreness, nonhealing wounds, headache, nausea, and fainting.  By not eating very much protein, you will also become hungry sooner, leading to weight gain from eating more calories trying to fill up.

Protein is found in meats, poultry, fish, meat substitutes, cheese, milk, nuts, legumes, and in smaller amounts in starchy foods and vegetables.  Eat these foods throughout your day to stay satisfied and energized.  A balanced diet is the goal.

References:

http://www.iom.edu/Global/News%20Announcements/~/media/C5CD2DD7840544979A549EC47E56A02B.ashx