The way I read it, Americans are substituting what used to be known as "good protein" with sugary junk. And it shows.
Yes, it's possible for a population's long term health to suffer due to what might be called excess nutrition, but these studies are called into question when they start teasing out what kind of nutrition is supplied...in general, height at maturity can represent a genetic maximum, based on the amounts of nutrients available. If it's in the form of protein and other nutrient dense foods, the higher average height is a result of good nutrition. If it is as a result of higher calories, but not nutrition, the body uses it to create height, but with a lower overall health profile.