Protein composition or protein quality can be measured in a number of ways. Most often you will hear the concept of bioavailability, which describes what percentage of the protein that you consume is actually absorbed into the bloodstream. Another indicator of protein quality considers how much of the protein is composed of essential amino acids, which are those your body cannot make itself and how much of the protein is composed of non essential amino acids, which are those your body can make itself. Obviously, sources that are rich in essential amino acids are of higher quality in this sense. In general protein quality ranks from animal sources to plant sources. Here's a short list of common foods ranked by their protein quality according to the concepts I just mentioned, starting with the most quality sources first.

In first place comes whey protein isolate, followed by whey protein concentrate. Then come x sources and meats, poultry and fish and seafood ranked somewhere in the middle Followed by soy protein and canola. Then you have combined plant sources like beans and rice. And last are the isolated plain sources like whole grain bread by itself or nuts by themselves. What this means is that all other things being equal, your improvements and body composition will be better if the protein is higher on the list predominate in your diet over the proteins lower on the list. But and this is a big bud, don't go out and buy buckets full of whey protein powder while consuming nothing else.

First of all, the differences between the foods are very small, accounting for only a few percentages of diocese's at the most. Second, there's nothing worse for your physical and mental health than a completely one sided diet. Even though nuts for example, aren't the highest quality source of protein. They're a great source of healthy fats and micronutrients. The same goes for other plant based proteins or fish and seafood. This also means that vegetarian athletes will see great results as long as they make sure to get their protein from a variety of plants sources to ensure they get all the essential amino acids through their diet.