Regarding the IQ part of the equation... It's pretty well known that poor nutrition will affect brain development. Some malnourished kids grow up smart and short, some grow up normal sized but with significantly lower intelligence, with all sorts of variances in between. You can't take the general truth (poor nutrition stunts growth) and apply it to an individual because everyone grows differently even with similar environmental conditions, but in general you're going to have a population with reduced capabilities across the board if they don't get enough of the right food when growing up.
My father in law is about 5 ft 4 inches, but all of his kids are well above average height, with one son over 6 ft. They're also all well above average for IQ. The difference between the father and the kids was nutrition growing up. My father in law grew up in a war zone during WWII, so his diet for years as a child was extremely protein limited. When he got to the US he made damn sure his kids got enough protein and the results really speak for themselves. They're as smart as their dad, but significantly taller and better physically developed. What makes this somewhat sad is that the difference may be as small as getting the equivalent of one egg per day, and there are still lots of places where one egg a week is considered a luxury. The people in those places are, as a group, going to be at a disadvantage.
Again, the generalizations can't be specifically applied to any one person because of natural variances. But on aggregate it's going to be true that a population with poor childhood nutrition is probably going to be stunted in one way or another. Anyone who has travelled much in third world countries sees this instantly. Almost everyone is *small* compared to us and it's surprising at first because those same people's relatives in the US are often "normal" size. You can sometimes even tell who comes from a rich family vs. who made their own fortune. The ones with a rich family are often strong and tall, the ones who made their own fortune are short and slightly overweight. The difference is due to when they started eating better food than everyone else. Again, this is a generality and may not be used to explain any one individual, because of natural variances...
Don't shoot the messenger, I've been to places where this is a real thing and saw it with my own eyes.