Heart patients do not benefit from omega-3 fats from fish and vegetable oils. However, these fatty acids seem to be good for those who also suffer from diabetes.
Kromhout and his colleagues studied the effects of omega-3 fats on cardiovascular diseases in 5000 heart patients in a 10-year long research project. These fats can be found, for example, in fish and certain vegetable oils. 'The omega-3 fatty acids had no effect on cardiovascular diseases in the patients in the study. But if these patients also had diabetes, an extra intake of omega-3 fish fatty acids seemed to lower the chances of fatal heart attacks by 50 percent. Omega-3 fatty acids also lowered the risk of severe abnormal heartbeat in these patients', reports Kromhout. 'In addition, in female heart patients who received extra doses of omega-3 fatty acids from vegetable oils, the risk of cardiovascular diseases went down by a quarter.'
The preoccupation with healthy omega-3 fats began forty years ago. Danish researchers discovered that the Inuit (or Eskimos) had ten times less probability of dying from a heart attack than the Danish people. The researchers attributed this to the diet of the Inuit, which is extremely rich in fats from fish, seals and whale blubber.
Kromhout discovered in 1985 that even a small amount of fish can offer protection from this lifestyle disease. Based on the now-famous Zutphen study - in which he studied the relation between fish and heart diseases in healthy middle-aged men from Zutphen - he concluded that the chance of getting a fatal heart attack becomes halved by eating fish once or twice a week. It was very surprising that this protection could already take effect by eating so little fish. While the Inuit eat as many as 400 grams of seafood daily, which gives 7 grams of omega-3 fats, the men in the Zutphen study received no more than 0.15 grams of the fish fats daily. 'My colleagues thought that I was practising homeopathy', laughs Kromhout. The results were affirmed by peer epidemiologists in the years after.
However, subsequent investigation was needed. A relation between fish fats and heart diseases in an epidemiological study does not necessarily point to a causal relationship. Other factors may also have played their parts. 'Fish often goes with a good glass of white wine, and we know that moderate alcohol consumption is also good for heart and vessels. So, is it the fish or the wine which brings about this protection effect?' asks the professor. 'To show that fish fats can actually prevent cardiovascular diseases, we set up the Alpha Omega Trial.'
Kromhout divided the test persons - heart patients between the ages of 60 and 80 - randomly into four groups. Each group got a margarine which tasted the same as that of the other groups but with a different composition, developed by Unilever. One group had margarine with only the omega-3 fats EPA and DHA; another had margarine with only the vegetable omega-3 fat ALA; the third group had a combination of EPA, DHA and ALA, while the control group had margarine with no omega-3 fats. Kromhout calculated that consuming the margarine with omega-3 fats spread on bread daily would be almost equal to consuming oily fish twice weekly, this being sufficient to bring on the protective effect. Neither the test persons nor the researchers knew which margarine was consumed by whom; that's called 'double blind' in jargon. 'This study is the first double blind nutrition study into the effects of omega-3 fats on cardiovascular diseases', says Kromhout. The researchers monitored the four groups for 40 months. They looked out for mortality due to heart attacks and for heart-related treatments in hospitals, such as angioplasty or a bypass operation.
Despite the amount of research work carried out into the link between omega-3 fats and cardiovascular diseases, it is still unknown how exactly fish fats can prevent these diseases. Marianne Geleijnse, epidemiologist and university senior lecturer in Human Nutrition, also the coordinator of the Alpha Omega Trial, thinks that omega-3 fats somehow prevent severe abnormal heartbeats. In order for the heart to perform well, a good conduction of electrical impulses through the heart tissues is necessary. 'We discovered that an intake of about 150 milligrams of omega-3 fatty acids daily resulted in no changes in blood cholesterol or blood clotting. The fatty acids are however quickly built into the cell membranes', says Geleijnse. 'This could have caused a better transmission of electrical impulses and fewer cases of abnormal heartbeats.' Another possibility, according to her, is a positive effect of omega-3 fats against artery clogging.
Now that the protective effects of omega-3 fats are found only in female heart patients and heart patients with diabetes, the question arises as to what consequences the Alpha Omega Trial has and whether the dietary advice from the Health Council to eat fish regularly still holds water. According to Geleijnse, the results of the study have to be viewed in relation to the test persons: heart patients who are being treated for the disease. 'It seems that the treatment of these patients in the Netherlands is so good that fish fats cannot make that any better', she explains. 'Only for those at high risk, such as heart patients who also have diabetes, can fish fats lessen sickness and fatality.' She feels that the trial cannot answer the question about the importance of fish in the diet of healthy people. Since healthy persons have a much smaller chance than heart patients of getting cardiovascular diseases, there would then have to be ten times as many people participating in such a study, say the researchers. It would then not be feasible practically and financially. But an overwhelming amount of epidemiological research has shown that fish is good for healthy persons too. Geleijnse: 'To prevent cardiovascular diseases, it is very important to have a healthy diet which includes fish once a week.'
The research is not without its share of sleepless nights. 'I was worried about many things, one of which being the financing of this project', Kromhout says, looking back. 'Also, when the number of deaths resulting from cardiovascular diseases was less than the half of what was expected, we really doubted if the study would lead to anything.' The professor feels that a major trial such as this will remain unique. Not just because it cost millions of euros, but mainly because preventive cardiology is on the rise. 'People with too high cholesterol levels and/or blood pressure - major risk factors for heart diseases - are already treated before they actually get heart problems', says Kromhout. 'A good thing, but it makes conducting research into the role of food in the cause of these diseases much tougher.'