MUM was right. One should have fish at every meal. About 40 years ago, the Inuit of Greenland were found to have markedly fewer fatal heart attacks than the Caucasians residing in nearby Denmark. Despite having a diet that included little in the way of fruit, vegetables and complex carbohydrates, the Inuit consistently had lower blood levels of cholesterol and triglycerides. Raised blood levels of these two types of fats cause coronary or heart arteries to harden and become blocked (atherosclerosis), which results in heart attacks.
A string of classic studies then identified the factor that protected the Inuit from heart attacks: namely, omega-3 fatty acids found in large amounts in fish. The Inuit diet is rich in whale, seal and fish. The two important omega-3s are called EPA and DHA, or eicosapentaenoic acid and docosahexaenoic acid, respectively. Both EPA and DHA must be obtained from food as they cannot be made in the body from other fatty acids. The best source of omega-3s is fatty fish.
Another group of people who also eat a lot of fish are the Japanese. While their omega-3 intake is only a quarter that of the Inuit, it is still 8 to 15 times that found in a Western diet. Since World War II, the Japanese diet has taken on a Westernised flavour. Still, coronary heart disease rates in Japan have remained under half of those found in the United States.
Dr Akira Sekikawa of the Shiga University of Medical Science and his co-workers set out to compare male Japanese living in Japan with male Japanese-Americans living in Honolulu and white Americans living in continental US. They found that the blood levels of omega-3s in the first group were 45 per cent higher than the second group, and 80 per cent greater than the third group.
The lower levels were found to be related to structural factors that indicate atherosclerosis. These included calcium deposits in the coronary arteries, as seen on X-rays, and increased thickness of artery walls, as seen on ultrasound. The researchers concluded that a very high intake of fish oil omega-3s can prevent atherosclerosis from developing. That is, eating lots of fish – or taking lots of fish oil omega-3 supplements – can help to prevent heart attacks.
Conversely, the intake of omega-3s among Norwegians is similar to that of the Japanese. However, the former also have a very high fat intake typical of meat-rich Western diets. Atherosclerosis is much more prevalent among Norwegians than among Japanese. What all this suggests is that while omega-3s can protect the heart, they can do so only if one’s diet is not abounding in saturated fats found in red meats.
But why would omega-3s – mere fatty acids – matter so much? Once thought to be just an inefficient source of energy the body uses when starved, fatty acids are now known to be very active molecules. They can act at the gene level to regulate protein synthesis. They can also act on signals at the cell level.
Since 2002, many of their beneficial effects in many different scenarios have been traced to resolvins and protectins, two substances made from omega-3s that have anti-inflammatory properties. Working in these and other ways, omega-3s can prevent heart attacks, a finding that has been confirmed in clinical trials. Huge clinical studies have shown that the increased intake of EPA alone or of EPA and DHA together will reduce the risk of coronary heart disease.
A 2002 study called the GISSI-Prevenzione trial showed that omega-3s reduced deaths from coronary heart disease by 30 per cent among Italian patients. A 2007 study showed that the use of EPA in Japanese heart patients reduced major coronary events such as heart attacks and sudden death by 19 per cent.
Interestingly, among Japanese in general, the risk of strokes is higher than the risk of coronary heart disease. This study also found that among people with a history of stroke, EPA cut their risk of a second stroke from 10.5 per cent to 6.8 per cent. The American Heart Association (AHA) recommends that healthy people eat a variety of (preferably fatty) fish at least twice a week. Fatty fish such as salmon, mackerel, herring and tuna are the best sources of EPA and DHA. Otherwise, one should take supplements of 400 to 500 mg of EPA plus DHA daily.
For those who already have coronary heart disease, the AHA recommends daily supplements of 1,000 mg of EPA plus DHA. Some patients may even need two to four grams of EPA plus DHA daily. However, such high doses could cause excessive bleeding in susceptible people. Use these mega doses only if your doctor prescribes them for you. If your ticker is still good, however, better to start eating lots of fish.