So what I'd really like to know is what happens with
cereal / vegetarian / vegan diet
plus cheap, easily available multivitamin
and mineral supplement pills
Maybe that's most of what's needed? The article does mention supplements, but only piecemeal.Of course, people still need protein. You won't get that from a cheap vitamin pill, and it's tricky to do right with a vegan diet. Fortunately I live in the USA and beef is relatively cheap. "Beef. It's what's for dinner".
BTW I have vague recall of Northern vs Southern diets in the US Civil War. The claim was that this played an important part in the health and strength of the soldiers. The Union soldiers had more beef and wheat in their diets. The Confederate soldiers had more pork and corn. The Union won.