I watched the Van Tulleken twin doctors last night. They were with an Arctic group of people that lived on walrus and whale blubber.
Their blood lipids were very good, except for one chap. It turned out he liked convenience foods of cake and tinned American hot dogs.
The twins had a ten day test where one ate the seafood blubber, one ate processed carbohydrate junk. The HDL to total cholesterol ratio of the blubber diet improved by 30%, whereas the junk diet showed a 30% detriment. They were amazed because consensus is that diet has little effect on cholesterol.