The nutritive value of proteins is determined by the composition of essential amino acids. From the nutritional point of view, proteins are classified into three categories.

1. Complete proteins: These proteins have all the ten essential amino acids in the proportion required by the human body to promote good growth. Examples are egg albumin and milk casein.
2. Partially incomplete proteins: These proteins, which lack one or more essential amino acids, help in moderate growth. Examples are wheat and rice proteins (Lys and Thr)
3. Incomplete proteins: These proteins are called incomplete proteins as they do not have any of the essential amino acids. Hence, they are not involved in growth. Examples are gelatin (lacks Trp) and Zein (lacks Lys).