What makes bitter melon bitter?

Sugar is the basic food that gives energy to humans. We feel it sweet because that is the mapping that our brain has given to it since it is the basic food giving us energy. Bitter melon has phyto nutrients and other compounds that can drastically reduce our sugar levels because of that reason our brain has given it the mapping of bitter taste.

All the tastes we feel for different food are just mapping signals given by our brain according to our body requirements, that is the reason even water tastes sweet and good when you are very thirsty.