Make it illegal to make statements that are not objectively true. E.g. you can't say that your product is "the best", you can only say specifically how it is better.
Put restrictions on advertising an idealized version of a product and then selling a lesser version. E.g. the difference between what fast food ads show versus what you get. I'm sure it would be difficult to completely fix that since it's so subjective, but we could probably get incremental improvements.
Improved health is a good one. It doesn't really mean anything.
Anyway, what I'm saying is that saying true things is what we already require. Human nature will pervert that system and follow the letter of the law; that's the literal system we have now.