I apologize, I never meant to suggest drinking the sauce - being water or oil - as the omega-3s in the sauce is minuscule compared to that in the flesh.
It's not miniscule, and actually worse when packed in oil because the oil-soluble fatty acids diffuse into the oil.
But even when packed in water, or just canned+cooked in own juices on the higher end, a substantial portion of the fats and oils escape the flesh and float to the surface during cooking. Draining the can discards fatty acids, it can be a surprisingly substantial portion.
