There was no scientific basis for providing these vegetables to babies in a form that they would accept, but it was a profitable practice that was compatible with the social pressure against prolonged breast feeding.

Various leaves contain antimetabolic substances that prevent the assimilation of the nutrients, and only very specifically adapted digestive systems (or technologies) can overcome those toxic effects.

Plant toxins are known to be specific for animal tissues; for example, a toxin will inhibit the action of an enzyme from an animal, but a plant enzyme that catalyzes the same reaction won’t be affected.

Plant defensive chemicals can have beneficial uses as drugs. Plants are important sources for chemicals used in chemotherapy of cancer, with the purpose of stopping cell division.