Protein is the buliding block of our body. Lack of protein means malnutrition. The problem with protein is that our body cannot manufactures alone the variety of amino acid types that constitute protein. Hence our body depends on protein it gets from external sopurces: the food we eat.
The foods which are richest in protein include all kinds of meat, chicken, fish and cheese – in short foods that come from the animal kingdom. In developed countries there is no problem making sure the population eats enough meet or fish.