There are many nutrients and foods currently being studied for their possible beneficial effects on the cardiovascular system. If you have read my previous article (here) you will already be aware that garlic shows excellent cardioprotective effects. However, perhaps the most extensively studied and most beneficial nutrients for heart health known to date are fish oils. As a result of the numerous positive studies, many healthcare professionals and regulatory bodies are currently recommending increased dietary intakes of fatty fish. Fatty fish include salmon, mackerel, tuna, sardines and pilchards, fish which store fatty acids in their flesh. These fish are beneficial because fish oil contains two important long chain fatty acids called docosahexaenoic acid (DHA, C22:6 (n-3)) and eicosapentaenoic acid (EPA, C20:5 (n-3)), which belong to the omega-3 family of fats. Both EPA and DHA are synthesised by plankton, and are then subsequently incorporated via the food chain into fish. When we eat the fish, we also eat their concentrated omega-3 fats.
Fish oils appear to have a multifaceted beneficial effect on human cardiovascular physiology. Most significantly, they appear to be able to prevent dangerous arrhythmias which can be a cause of heart attacks. Similar to the sulfur components of garlic, EPA and DHA may also have beneficial anti-thrombotic effects by decreasing levels of thromboxane A2, a short lived hormone that stimulates platelet aggregation and vasoconstriction. A thrombus is a blood clot inside blood vessels, and these can be dangerous if they get trapped in the small vessels of the heart and brain, leading to a heart attack or stroke, respectively. Omega 3 fish oils may also stimulate nitric oxide levels in the endothelium, leading to a relaxation of the vessels and a decrease in blood pressure. Fats in fish also appear to be able to retard the growth of atherosclerosis by inhibiting both cellular growth factors and the migration of monocytes, two processes necessary for the formation of plaques. And if that was not enough fish oils may also be able to lower risk factors for heart disease, for example by reducing triglyceride levels and inhibiting apolipoprotein B production.
High intakes of fatty fish therefore appears to be particularly cardioprotective, and these effects have been extensively researched. Studies looking at the beneficial effects of omega-3 fatty acids have used both fish and fish oil supplements. It appears from this research that there is a an equivalence between the benefits from supplements and from fish. For example, a study published in the American Journal of Clinical Nutrition in 2007 compared the consumption of omega-3 fats from fish with that of fish oil capsules. The study found that EPA and DHA from fatty fish or fish oil capsules were equally good at raising blood lipid levels of the omega-3 fats1. Based on this evidence, it should not matter if the omega-3 oils come from either fish or fish oil supplements. However, other evidence suggests that eating fatty fish might not be a such good idea because of the levels of pollution contained within some bodies of water. Just as fish can accumulate the oils from plankton, they can also concentrate the pollution and contaminants contained within their structures. This can lead to the development of contaminated fish.
Contaminated fish can contain dangerous levels of carcinogens in the form of PCBs and dioxins as well as the chemicals dieldrin and toxaphene. These chemicals can build up in people who consume fish on a regular basis. Eating oily fish might not therefore be the best way to get the beneficial effects of omega-3 fats. For example, a study published in the Journal of Nutrition in 2005 demonstrated that the benefits of eating farmed fish is outweighed by the damaging effects of the carcinogenic chemicals it contains2. These researchers found that wild salmon have significantly lower levels of contamination than farmed salmon, but that neither farmed nor wild salmon can be consumed at rates that provide the recommended levels of DHA or EPA while maintaining acceptable level of carcinogen risk. Because capsules are available that have had the dangerous contaminants removed, it seems prudent to stick to supplementation with capsules and to avoid fish altogether unless you know it is safe. The benefits of fish oils can therefore still be obtained without the need to consume contaminated fish.
While vegetarians cannot consume fish oils, they do not have to miss out on the healing properties of essential fats. Omega-3 fats are also present in flax seeds and consuming the oil has been show to elevate levels of beneficial omega-3 levels in the body in a similar way to fish oils. For example, a paper published in the American Journal of Clinical Nutrition in 2008 demonstrated that the consumption of the oil derived from flax seeds for 12 weeks was sufficient to elevate erythrocyte levels of DHA and EPA, which compared favourably to a fish oil supplement taken by other subjects3. The subjects took 2.4 g (4 capsules) of flax oil with each capsule providing 598.3 mg of alpha linolenic acid (ALA, C18:3 (n-3)), which is converted in the body to EPA and DHA. Obviously because flax is not contaminated with carcinogens, non-vegetarians could also choose flax oil in order to raise their blood levels of omega-3 oils. However, whole flax seeds must be milled to break open the protective seed coat to allow digestion.
RdB
