In this case, fish oil sources matter. Oxidation, polychlorinated biphenyls (PCBs) matter. You can filter for quality sources that meet the International Fish Oil Standards here: https://certifications.nutrasource.ca/certified-products?typ...
* Everyone is excited about X which improves Y
* Studies looking into X find no improvement in Y and/or some people don't notice X improve Y
* People invested in X argue that they are not timing/dosing X properly, or people do not have the right form of X
It usually descends into absurdities where you are supposed to find this rare unicorn brand that has the proper quality (for now, who knows next year!) then dose it at some exact time before bed time, but avoiding calcium or citric acid or something because that would nullify it etc etc.
Supposing the supplement even ever worked, it simply is not practically useful with such constraints. I'm not going to get a PHD in fish oil quality in order to achieve some single digit risk reduction of heart disease.
The paper pretty much says fish oil + exercise does not increase performance ("inconclusive") and some evidence for improved fat loss. Many of the studies reviewed by the paper show evidence that heart rate is lower during "submaximal" exertion.
GP links to a list of "certified" fish oil sources, so if you wanted to at minimum test for yourself, you could just pick one from the list before you pursue your fish oil PhD.
Most people experience minor if any benefit from these things. The things which really cause benefits are healthy eating and exercise in general. If you go from eating fast food and barely walking to eating whole foods and deliberately exercising 5-7 days a week, you'll almost certainly feel a major difference. What exactly caused that difference, where you crossed the line, is unclear; but it doesn't matter, IMO people should eat well and exercise reasonably anyways.
The body is a complex system. Just because our minds prefer simplicity doesn't mean our bodies will respond simply. People that are into the minutiae of nutrition and supplementation are obviously willing to do their homework to get the benefits.
"Supposing the supplement even ever worked, it simply is not practically useful with such constraints. I'm not going to get a PHD in fish oil quality in order to achieve some single digit risk reduction of heart disease."
Nobody is asking you to do anything. We live in a society where most foods are fairly processed, most supplements are bogus, most claims are BS, etc. There's an overwhelming amount of data on the benefits of Omega-3s now, and to get the benefits you need to actually take quality Omega-3s. Rancid fish oil won't give much benefit, and most fish oil is likely shit. The supplements industry isn't regulated like medicine.
I just saw an article written somewhere today that there's a pill being created so that we don't have to exercise anymore. Just buy the pill and that's good. I'm going to do that one!
You don't need a PhD, just read the amazon reviews for different brands.
"This faculty position requires a Ph D."
"I don't have that, but I read Amazon reviews for different brands."
With fish based sources, there's a lot to worry about and making sure you get from a reputable source. With algae based, there's less environmental impact and less worry about what else is getting in there, etc. This brand's been good for me: https://iwilife.com/