A few years ago, i started using cod-liver oil. I believe that the boost i felt, at that time, came from the pre-formed vitamin A in it, though i had been convinced by various writers that its omega-3 was a good balance for any excess omega-6 that i was getting elsewhere in my diet. I'm not so sure about that latter part, now.
I decided to discontinue the CLO, as i am concentrating on eating liver more often ... and my husband bought a large lot of grass-finished ground beef which comes with a better o-3 ratio. Almost immediately i started seeing better energy and fatigue-resistance.
Ray Peat would be nodding his head. ALL polyunsaturated fats have shortcomings -- on this we both agree. And despite backpedaling by some "obesity experts," there IS convincing data that PUFAs inhibit thyroid uptake by cells ... not least my own subjective experience. Cuz who cares what experts say if your body tells you they're wrong?
I have a LOT of ambivalence about Peat's ideas. Some of his writings reflect my nutritional experiences, and some of it seems a bit too far "out there" to be thoroughly believable. Certainly, his opinion of gelatin/glycine APPEARS to be completely on-target ... but when it comes to his point-of-view about sugar? No.
Over the last five years i've tried a lot of things that other people have reported worked for them -- some worked for me too, and others did not. It really amazes me how much difference there can be between two comparatively similar people, and how much similarity between very different ones. Well, of course microbiology IS microbiology for us all, even though it's affected by our histories of infections and deficiencies, and directed (in the theatrical sense) by our genomes. Starting from a paleo template, we can suggest possible solutions to people having health problems that are strongly influenced by lifestyle, but there doesn't seem to be any such thing as a never-fail answer ... despite SOME things being an always-fail situation -- like the ADA diet!
It just looks like the vitamins A and D don't make up for the downside of CLO -- its polyunsaturated oils. So i'm bidding adieu to a supplement i thought i'd always use. Cod-liver oil IS a good product for some people in some situations, but i don't think it's optimal for ME, when compared to weekly liver and plenty of grassfed beef/lamb.