First and foremost, you have to remember that restaurants are businesses and they have to stay in business. And though everyone thinks they want grass fed beef, most people actually prefer the taste of corn fed - it is less dry, more marbled, and less gamey, not to mention much less expensive than grass fed.
For the sake of argument and illustration I will presume that certain articles of ordinary diet, however beneficial in youth, are prejudicial in advanced life, like beans to a horse, whose common ordinary food is hay and corn.