Fish oil, whether in the form of dietary supplement capsules or from eating fatty fish, does not lower cholesterol. In the April 2002 issue of "Circulation," Roberto Marchioli, M.D., reported that for 11,323 subjects, with half getting 1,000 mg per day of fish oil omega-3 fatty acids daily, neither total cholesterol nor LDL-cholesterol (the "bad" cholesterol) went down in the treated group over the course of the 42-week study. The cholesterol-lowering misunderstanding is common, because it is widely accepted that fish oil prevents heart disease, and for most people, cholesterol is synonymous with heart disease. Fish oil, does however, reduce the risk of heart disease by 20 to 30 percent.
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High levels of cholesterol in the blood are a known risk factor for heart disease. Every day, we consume about 300 milligrams (mg) of cholesterol from foods and make about twice that much in our liver. And, every day, our bodies use up about 900mg. If this unbalances on the plus side, blood levels increase and cholesterol gets deposited in artery walls. Prescription "statin" drugs inhibit cholesterol synthesis. The other means of lowering cholesterol is to absorb less from foods, either by eating less or co-consuming foods that block absorption. Examples of absorption inhibitors include oats, barley and phytosterol-containing margarine. The two approaches can be combined.
How Fish Oil Works
The proposed mechanisms for how fish oil reduces the risk of heart disease include a combination of anti-inflammatory activity, preventing irregularities in heartbeat, i.e., arrhythmias, preventing formation of blood clots in narrowed arteries and relaxing artery walls. Reviews by H.C. Bucher in the March 2002 issue of the "American Journal of Nutrition" and C. Wang in the July 2006 issue of "American Journal of Clinical Nutrition" state that eating fish or taking fish oil capsules on a regular basis reduces the risk of fatal heart attacks by 20 to 30 percent.
The active parts of fish oil are the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). One function for EPA and DHA is as precursors for anti-inflammatory prostaglandins. Another is to increase the flexibility of cell membranes. Fish oil also lowers blood triglycerides--another heart disease risk factor--but only when omega-3 intake is on the order of 2g to 4g per day. Plants products, such as flax seed oil and chia oil, contain a different type of omega-3 fatty acid--alpha-linolenic acid (ALA). This omega-3 fatty acid needs to be converted to EPA or DHA to have health benefits. The conversion process is inefficient.
FDA-Approved Health Claims
In September 2004, the U.S. Food and Drug Administration (FDA) approved a Qualified Health Claim for some of the omega-3 fatty acids. The language allowed for a food or dietary supplement label intending to use this claim says that supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease. The label has to say how much EPA and DHA there is per serving. Note that the claim does not apply to alpha-linolenic acid (ALA), as human tests with ALA have not been convincing.
The American Heart Association (AHA) recommends eating fish, preferably fatty fish, such a salmon, twice a week. The AHA goes on to state that an alternative, especially for people with diagnosed heart disease, is to consume about one gram of EPA and DHA per day from food, plus supplements. The supplement facts label on fish oil supplements states how much EPA and DHA they contain.