(It's not clear to me that malnourishment leads to multiple modes, rather than just decreasing the mean while probably increasing the variance, because I think damage due to malnourishment is linear, and it's probably the case that many different levels of severity of malnourishment are roughly equally well represented.)

Not everyone's malnourished, though - a significant number of people are into diminishing returns, nutrition wise. It's very nonlinear in the sense that as long as there's adequate nutrition, it plate-outs - access to more nutrition does not improve anything.