The brains of newly born children require 87% of their metabolic energy to grow and develop normally. In five-year-olds, the figure is 44%, and even in adults -- where the brain is only 2% of the body's weight -- the figure is still 23% to 27%.
Obviously, any competition for the energy required for a young brain's development would seriously hinder that development. We know that the brains of malnourished children don't develop normally. Now we also know that parasites and harmful pathogens compete for the body's energy, as well. Some feed on the host's tissue directly, or actually hijack its molecular machinery to reproduce. Other parasites that live in the gut stop their host from absorbing food.
The inescapable conclusion is that this "perfect storm" of hunger, poor nutrition and persistent disease combines to produce low IQ in children in developing countries -- with devastating results.