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On Omega-3 On Omega-3 Fatty Acids and the Heart


bulletRapid protective effect of alpha-linolenic acid in 
heart-attack survivors shown by survival curves
bulletMarked reduction in myocardial infarction and 
no sudden deaths in experimental group during 
trial of Mediterranean diet
Five years after being assigned to a diet rich in alpha-linolenic acid (ALA) (a "Mediterranean" diet), survivors of a first myocardial infarction manifested a markedly reduced rate of recurrence of myocardial infarction, other cardiac events, and overall mortality (de Lorgeril et al, 1994).  A reduction in coronary events and cardiac deaths of close to 70% was achieved in this trial without a reduction of serum cholesterol, triglycerides, or an increase in high-density lipoprotein (HDL) compared to controls, in contrast to previous unsuccessful dietary secondary-prevention trials.  A difference between this and previous secondary-prevention trials is the level of ALA provided the treatment group; in this study, the concentration of ALA was increased by 68% and that of linolenic acid reduced by 7% in the experimental group.  


After randomization patients in the experimental group (n=302) were advised to adopt a Mediterranean-type diet consisting of more bread, more root and green vegetables, more fish, less meat (beef, lamb, and pork to be replaced by poultry), no day without fruit, and butter and cream to be replaced with supplied margarine.   Similar to olive oil, the margarine had 15% saturated fatty acids and 48% oleic acid but 5.4% 18:1 trans fats; it also was slightly higher in linoleic acid (16.4 versus 8.6%) and higher still in ALA (4.8 versus 0.6%) than other margarines.  

To avoid influencing the behavior of controls, control patients (n=303) received no dietary advice and were not evaluated as to food intake for the first 4 years of the trial. At the 52-week evaluation of plasma fatty acids the experimental group showed significantly higher levels of oleic (p less than 0.001), alpha-linolenic (p less than 0.001), and eicosapentaenoic (p less than 0.001) acids and lower levels of stearic (p less than 0.001), linoleic (0.002), and arachidonic (p=0.005) acids.  Control subjects experienced 20 deaths (8 sudden deaths) and treatment subjects 8 deaths (no sudden deaths); the probability of survival by the product-limit method (Kaplan Meier) was 0.82 in the control group and 0.955 in the experimental group (p=0.02), with a risk ratio of 0.30 (p=0.02).  The risk ratio of cardiac death was 0.24 (0.07 to 0.85, p=0.02).   Survival differed significantly in favor of treated subjects (p less than 0.003).  

Of course, as with any study involving humans we must wonder at how strictly the subjects complied with the diets they were provided, as well as how often and to what extent subjects in the "diet" group might have sneaked a quick cream puff now and then, thus doing strange things to the results.  That is why results of dietary experiments involving animals whose every morsel is regulated can be so much more reliable.  But it is always to some extent risky to generalize from animal results to human.  The study discussed above has in its favor the length of time it ran and the number of subjects enrolled.   In addition, all subjects had experienced at least one heart attack, and that history might have disposed subjects in the "diet" group toward compliance.  

de Lorgeril M, Renaud S, Mamelle N et al:  Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease.  Lancet 1994; 343(8911):1454-1459.