Polyunsaturated fats have been shown to lower cholesterol. However, that's total cholesterol, and it typically drops at the expense of HDL. If you want to drop your total cholesterol, which is an arbitrary number, at the expense of HDL, that would be misguided. While total may drop, often your ratio of HDL:LDL and HDL:triglycerides degrade. On another note, while eating a diet high in saturated fat and low in polyunsaturated fat typically increases cholesterol, it's because you are seeing a sharp rise in protective HDL and ratios improve significantly.
Another thing you have to recognize is that there is more than one type of polyunsaturate fat. Omega 6 polyunsaturated fats found in animal products is primarily arachidonic acid - while it is pro-inflammatory, the entire healing process that the body relies on depends on inflammation. Without arachidonic acid, you cannot heal appropriately. While ruminant meat seems to be the most beneficial, that doesn't mean eating chicken is going to kill you because it has more polyunsaturated fat. It is primarily arachidonic acid.
Plant-based omega 6 polyunsaturated fat is linoleic acid. This is where the problem comes in. Soybean oil, canola oil, cottonseed oil - this is linoleic acid. It is inflammatory and not really necessary like arachidonic acid. Nuts are high in linoleic acid, but I'm not going to sit here and tell you that nuts = soybean oil. That is a ridiculous assessment. You can eat nuts, but treat them as a condiment/topping and not a dietary staple. You shouldn't be snacking on nuts every single day, but if you're tossing some on a salad or having an occasional handful, you'll be okay. If your biggest indulgence is some dark chocolate and a handful of pecans you're way ahead of the game.
Omega 3 is even dicier. Omega 3's are more unstable than omega 6's, so it's even more important to focus on quality here. Flax, hemp, chai, walnuts and other plant sources of omega 3's contain ALA-based omega 3, which is mostly useless by the human body. It has to be converted to EPA/DHA, and the processes are very inefficient, especially for men. I would recommend NOT eating flax, hemp and other omega 3's from plants. They're incredibly unstable, and please do NOT bake with them. I'm less concerned about walnuts because they're a whole food, but always, enjoy in moderation and not as a staple food.
Omega 3's from animals (like fish) is the EPA/DHA that scientists say we "need". I don't know if I believe that, but I'd much rather eat animal-based omega 3's than plant-based omega 3's.
I still don't care for a high PUFA diet. It seems to be pro-inflammatory. I refuse to take fish oil. IMO, if fish oil makes you feel better, that is a huge issue because you're so inflamed that it's actually helping. IMO, the ideal diet is a low PUFA diet. FWIW, omega 3 is "linolenic" acid, not to be confused with "linoleic" acid mentioned above, which is a plant-based omega 6.
Got all that? Me neither.
Polyunsaturated fat - Wikipedia, the free encyclopedia
α-linolenic acid (ALA) = parent omega 3, largely plant-based (18 carbons, 3 double bonds), highly unstable.
Breaks down (inefficiently) in the human body into animal-based eicosapentaenoic acid (EPA, 20 carbons and 5 double bonds) and docosahexaenoic acid (DHA, 22 carbons and 6 double bonds).
So since fish oil contains more carbons and double-bonds than flaxseed oil (ALA-based), that means fish oil is the most unstable of all! No WONDER fish goes bad so fast. Do you really want to consume this isolated oil that's been in the back of a hot truck and under bright lights on a shelf at room temperature all day? HELL NO, NOT ME! My opinion.
Linoleic acid (18 carbons, 2 double bonds) is the shortest-chained n−6 fatty acid found in plants.
That breaks down into animal-based arachidonic acid (20 carbons, 4 double bonds) in the human body.
Isn't it funny that generally foods with higher omega 6 spoil faster?
Beef can be eaten rare and can sit out on the counter for a few hours at room temp. Its PUFA is low.
Pork can be eaten medium. It has a moderate PUFA level.
Chicken has to be well-done. It has a high PUFA level for an animal.
Fish is mostly PUFA and goes bad very, very quickly.
Just remember to store all your PUFA's in the refrigerator or freezer. I refrigerate all my nuts. I don't let them sit out. Especially flax. If you have flax (for some awful reason, it tastes terrible and I see no benefit to consumption) keep it in the FREEZER and for God's sake DON'T BAKE WITH IT. That's the industrial method for making varnish.
Don't put your trust in anyone on this forum, including me. You are the key to your own success.