The main problem in south-Asia regarding food shortage are undernourished children. One big reason is the low social standing of women. Therefore young mothers often are uneducated and not able to raise their children properly.
Most sub-Saharan countries suffer from a dramatic infant mortality rate and a high rate of people who are unable to meet their calorie demand.
The main reasons are bad governance, military conflicts, political instability and a high rate of HIV-infected people.