I just ran across this article. I haven't really checked the science behind it, but what they are saying is that women with broader hips have fat stores of omega 3 fatty acids in their thighs and butts. Belly fat apparently is lower in omega 3's. The brain is built mostly of lipids. This article says that during child development, the brain of the fetus is built from the reserves of omega 3's that the mother has in her thighs. It says that a skinny pregnant woman can supplement omega 3 fatty acids, but that your body prefers to use stored lipids for building baby brains.