But then, there is the nebulous world of dietary supplements. Not considered a drug, dietary supplements are governed by a different set of rules from conventional food (as per the US Food and Drug Administration). As worded, the manufacturer is responsible for the safety of a supplement, and the FDA can only act after it has reached the market. Culturally, the general populace embrace supplementation as a kind of nutritional talisman to head off dietary misbehavior - parent make their kids take multivitamins, students voluntarily quaff high caffeine products to stay awake, and athletes consume expensive products with dubious scientific reproducibility, and backed only by anecdotal testimony. Supplements are taken voluntarily as food, to treat a potential illness - and is a multi billion dollar business the world over.
The objectionable thing with supplementation is how rife the practice is with pseudoscience (cherry picking of evidence, scientific obfuscation, dubious credibility), but the subject of predictive nutrition is a complex one. Take, for example, the common body building supplement L-carnitine. It's a non-essential amino acid already found in meat, and as such, is thought to be generally safe to megadose with. But that doesn't take into account what our gut bacteria does to it. Bacteria convert L-carnitine to a compound known as TMAO, which is biochemically linked to the progression of artherosclerosis. You can buy pills of the stuff as health food, pop them without medical supervision, maybe get bigger (?) - but we have reproducible scientific evidence that you are actually feeding your gut bacteria with L-carnitine - and they're pooping out stuff that can promote heart disease.
In general, in the modern world of food, choice is abundant, and using supplements as a crutch is a bad idea, and not a substitute for smart selection of a range of food sources to promote a healthy lifestyle.