Tens of thousands of studies later, things haven’t gotten all that much clearer: We still don’t have anything close to a firm grasp of what fish oil can do and what it cannot. And lately, things have only gotten weirder.

Most experts acknowledge that fish oil does have some modest benefits in certain circumstances. Omega-3, its star nutrient, has been shown to lower levels of a fat associated with heart failure, help prevent premature births, and improve infant formulas. But these are a far cry from the game-changing promise of the early studies. That promise, over the years, has gotten lost in a tangle of theoretical possibilities, Nestle told me. Fish oil contains two distinct types of omega-3, DHA and EPA; maybe only the former is providing the benefit. Or maybe only the latter. Maybe the benefit comes only from pairing the two. Maybe neither does anything unless it’s consumed with other parts of the actual fish.

And that’s just the beginning. Maybe the benefits have less to do with fish itself and more to do with the fact that if you’re eating fish, you’re probably not also eating a hamburger or a pork chop. Maybe they have to do with your overall diet. Maybe they don’t have to do with your diet at all. Maybe it’s just that fish eaters tend to be wealthier and, not unrelatedly, healthier in the first place. Maybe it’s something else entirely.