adverts don’t really tell you what it is they’re meant to do
They don’t because they can’t. All the supposed health benefits associated with ‘friendly bacteria’, and antioxidants and other guff are disseminated by paid patsies in the press. Thats because if you have a totally unproven point to make you can write about it at will as ‘news’ or ‘fact’ but you can’t make unfounded claims on labels or adverts.
So you place adverts in the media that make hazy claims about how you can overcome a general sense ‘blah’ and non-specific ‘hurumph’ with a product, or use even more vague claims like “excellent source of antioxidants” without saying what antioxidant might do.
Then you get the press to talk about specific, but un-demonstrated, benefits of your product in the column inches around the advert, or in the ‘news’ between the adbreaks.
So if an advert or a label doesn’t make a very specific claim then the product doesn’t really do anything measurable at all.
The only exception is cosmetics, where you seem to be at liberty to make any claim about a product on the basis that if a cosmetic could actually achieve any active effect, it wouldn’t be a cosmetic but a pharmacutical.