1 in 5 children are obese, and may die before their parents, what does that mean for the population?

I was watching a documentary on American obesity, and we have the highest obese population on the planet, and 1 in 5 are considered obese, and estimated to die before their parents. This will be the first population in recorded history that is projected to die before their parents.

If this number is climbing, and this generation is basically a genetic dead end, with parents being too old to keep having children. Won't this create a huge gap in the time-line of humanity? Say in 40 years, won't the population of America, and perhaps the developed world, plummet drastically?