Thirty different plants a week

The number comes from a large gut study: people who ate more than thirty kinds of plants a week had more varied gut bacteria than people eating fewer than ten. That's an association in a survey, not a trial, and "more varied" is not yet "healthier" in a proven way. Evidence: worth trying

The brain claims you'll hear attached to it, dark berries growing new neurons and so on (whether adults grow new brain cells at all is disputed), are mostly from animal studies. Evidence: decent The honest reason to do it: it's the easiest food rule there is, it pushes you toward the foods every guideline agrees on, and it makes shopping slightly more interesting.