Beef and Tofu and Beans, Oh My!

Proteins are mad up of molecules called amino acids, which are the "building blocks" of your body's cells.
They are key to the growth of muscle tissue. Unknown to many, however, is the fact that high - protein foods empty from the stomach very slowly, making you feel fuller and burning more calories to digest than carbs or fats.
Protein also has a gentler effect on blood sugar, so you avoid the blood-sugar spikes and crashes caused by many carbs.
Essential amino acids are those that the body cannot synthesize and, therefore, must come from food sources. Although there are varying estimates, most experts say that between 0.2-0.8 grams of protein per bodyweight per day is sufficient. Heavy training and bodybuilding may require higher intake( I get about 1.0-1.5g/lb./day)
Most sources find that more than 20-30g per meal is not readily absorbed at one time. Spread your intake throughout the day.
Finally, fish, eggs, lean meat, whey, and dairy are the best sources. Soy, nuts, and beans are other excellent sources to mix in on a regular basis.
Of course, always check with a doctor or nutritionist to help you determine your specific intake.