I take it to mean "get most of your nutrition from plant-based sources". Some meat, dairy, etc. are ok if you want, but most of what you eat should be plant-based food. Apart from grains, its hard to eat too much plant based food - whether measured in mass or calories.

Sheesh... it's not that hard to understand. There is more to healthy eating than quantities and exercise.

And besides that consumables that aren't labelled dangerous by the USDA or FDA (I don't know how they factor into this discussion - not everyone lives in the US, and I see them mentioned in the article) can still be dangerous to an individual if you have a certain condition. Easy example: nut allergies. Others: Celiac disease, diabetes. etc.

And, eating nothing but something that might even be considered healthy can also be fatal if you don't supplement it, no matter how moderate your intake.

The GRAS (Generally Recognized as Safe) category is a wide open door, though.