The Latin verb nutrire, to feed, suckle, or nourish, produced the noun nutritio, from which English borrowed nutrition through French in the fifteenth and sixteenth centuries. The same root traveled a parallel path through Old French norice to give English nurse and nourish, which is why a hospital nurse and a nutrition label share an ancestor. Later coinages filled out the family: nutrient for the nourishing substance itself, and malnutrition, a nineteenth-century term for nourishment gone wrong.
In Italian and Spanish the root stayed closer to the verb: nutro is the first-person singular present of nutrire and nutrir respectively, so the bare word means 'I nourish.' Modern brand builders keep returning to the root because it compresses a promise of health into a few letters, which is why nutri- and nutro- prefixes appear on pet foods, supplements, and apps worldwide. Onutro fits that pattern, though with no archived content, the original intent behind this particular spelling remains unknown.