Cool, so malnourishment throughout life will only account for at most a 30% decline. Or is that "inherited" because it's environmental, but determined by parents?
The assumption is your environment is pretty similar to everyone else's environment, which means you don't die of hunger or get boiled in acid.
But you raise a very important point, and you're right: as far as I'm aware, latest evidence says that being malnourished as a child does significantly impact intelligence as it does height (stunting). Though I believe the last piece of work I read on it claimed the effect was smaller than previously believed. That was ~2 years ago.
For any given trait X, the question about how much it is "inherited/genetic" or "environmental" is a commonly used shorthand, even amongst professionals, but it can be subtly misleading. All traits are 100% inherited, and all traits are 100% environmental. What do I mean by this? How is the ability to speak Russian genetic? How is the colour of your hair environmental?
Well, put it this way: is the difference between a human child brought up in a Russian family and their pet dog who has lived with them for the same time genetic or environmental? And what is the difference between a pair of identical twins, one of whom bleached their hair with peroxide–genetic or environmental?
The above are of course exaggerations, but they're just obvious examples. The correct way of phrasing the question is this: given a population A, what percentage of the variability of trait X is inherited and what percentage is environmental? Given the population of mammals, is the ability to speak Russian mainly genetic? Yes. Given a pair of identical twins, is any difference in their hair colour environmental? Also yes.
So, to the question as to how much of a decline in intelligence can be accounted to malnourishment throughout life (and how much to other environmental factors, genetics, etc.) we need to specify what population we're talking about. I'd be willing to bet that:
1- the variability in intelligence due to malnourishment in the population of middle-to-upper class children is negligible,
2- the variability in intelligence due to malnourishment in the entire child population of a developed country is detectable,
3- ...and the variability in intelligence in the due to malnourishment in the worldwide child population is significantly higher.
