“Good fats” provide the omega-3 fatty acids.
Fish oil and flaxseed oil are very good for you because they provide the omega-3 fatty acids that can substantially reduce the incidence of sudden cardiac death and may help prevent some forms of cancer, but you only need about three grams a day for the protective benefits.
Assessing the Two Versions of the Diet Dean Ornish, MD, Recommends
“Prevention” vs. “Reversal” Diet Guidelines
“Good fats” provide the omega-3 fatty acids. These can be found in high concentrations in both fish oil and flaxseed oil — 3 grams a day is all you need. The omega-3 fatty acids have many benefits. Fish oils are believed to protect blood vessel walls from the harmful effects of LDL cholesterol, including a reduction in sudden cardiac death of more than 50%-80% in some studies. Since the fish that are in omega-3 fatty acids also may be high in mercury, cholesterol, and fat, these provide the benefits of fish without the potential concerns.
Some studies suggest that flaxseed oil may promote prostate cancer growth whereas fish oil may inhibit it. These studies are not definitive but they are worrisome, so until the data are sorted out, it may be wiser to take fish oil if you’re a man.
Fish also contains omega-3 fatty acids, which have been shown to decrease blood pressure and triglyceride levels, and increase clotting time.18 Recent research has shown that fish containing omega-3 fatty acids may help reduce the risk of cardiovascular disease when eaten as part of a heart-healthy diet. Additional studies have shown that eating fish high in omega-3 fatty acids at least once a week is associated with a reduction in the risk of primary cardiac arrest.19 The types of fish containing the highest amounts of omega-3 fatty acids are herring, salmon, mackerel, sardines and swordfish. Patients should be encouraged to eat fish and shellfish at least once per week
Food and Nutrition Board, Institute of Medicine (2002). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients)