Ditto, individual and genetic factors that can influence whether any particular diet is optimal.
Also, it's difficult to extrapolate anything about diet and health from the pool of former/retired athletes, because many former athletes tend to over indulge to make up for years of sacrifice.
And it's difficult to say whether those years of sacrifice to be competitive strengthened or weakened their bodies for the long haul.
Offhand I can think of two Tour de France champions who gained quite a bit of weight in retirement, a few who stayed relatively fit and trim, and two who died of cancer (Anquetil at 53; Fignon at 40) despite seeming to be reasonably fit and trim for their retirement ages. It's been awhile since I checked the lists of ages and deaths of grand tour champions but overall I got the impression that there was no difference between them, in retirement, and the average guy the same age.
Same with professional boxers, the other sport I've kept up with for decades. Many over indulge, drink too much booze, eat too much, and reckless living plagues many athletes whose sports exposed them to chronic brain damage. Others inexplicably lived long lives, minds still sound.
Genetic luck of the draw seems to be the most significant factor.