What I learned in my parasitology class is the following. Areas with famine, which are generally developing (third world) nations. They, besides having famine, generally have poor sanitation, poor disease control, basically poor everything that you would take for granted in the U.S.
The big bellies are parasites living in their gut. Many parasites inhabit different parts of the intestine. The big bellies are due to worm types of parasites, they get huge! They sit in the intestines and consume (i.e., parasitize) the (little) food that the people do eat. A bad thing about that is that the parasites can consume certain vitamins that the people need, so the people have to eat more to be able to get the vitamins or whatnot, and by doing so they further feed the parasites.
Parasites are *bad* things!