NEW ORLEANS — The value of fish oil for the secondary prevention of cardiovascular-disease events was placed in some doubt with results from a diet study that involved about 200 patients.
“We saw no difference between the American Heart Association's Step II diet and the Mediterranean diet for preventing major cardiovascular events in patients following a myocardial infarction,” Dr. Katherine R. Tuttle said at the annual meeting of the American College of Cardiology.
In addition, patients who followed either of these diets had significantly fewer cardiovascular events during follow-up than did patients who had usual care and did not adhere to a formal diet, said Dr. Tuttle, director of research at the Providence Medical Research Center in Spokane, Wash.
“What was compelling was how well both diets did compared with a usual-care diet. Clearly, patients who are motivated to adhere to a diet will do substantially better” than will those who aren't, commented Dr. Paul Ridker, director of the Center for Cardiovascular Disease Prevention at Brigham and Women's Hospital in Boston.
But some experts were skeptical about whether the new results, which involved a modest number of patients, proved that a diet rich in omega-3 fatty acids from plant and fish sources was no better than the standard level of omega-3 fatty acids in the AHA Step II diet. This aspect of the study involved 50 patients who began and 45 who completed the Step II diet, and 51 patients who began and 48 who completed the Mediterranean diet.
The study had “too few patients” to make any firm conclusion about the incremental value of a diet rich in omega-3 fatty acids, said Dr. Christie M. Ballantyne, director of the Center for Cardiovascular Disease Prevention at Baylor College of Medicine, Houston.
In the 2006 revision of its diet and lifestyle recommendations the AHA stated: “Patients with documented coronary heart disease are advised to consume about 1 g of EPA [eicosapentaenoic acid] and DHA [docosahexaenoic acid] per day, preferably from oily fish, although EPA and DHA supplements could be considered in consultation with their physicians.” This AHA recommendation has been in place for several years. EPA and DHA are the major omega-3 fatty acids found in fish oil.
The Heart Institute of Spokane-Diet Intervention and Evaluation Trial (THIS-DIET) randomized 101 patients within 6 weeks of a first myocardial infarction who were willing to go on one of the study diets. Another 101 similar patients who were not willing to be assigned to a diet were followed in a usual-care control group. All three groups were similar at baseline for clinical and demographic measures. Patients in the diet group had seven individualized diet counseling sessions spaced throughout the first 2 years of the study, as well at least six group sessions a month. Patients were responsible for preparing their own foods.
The major difference between the Mediterranean and Step II diets was in the level of omega-3 fatty acids consumed. For a focus on this difference, management of patients in all three groups was structured so that patients would not lose weight during the study, an effect that would have confounded the results. The strategy worked: Patients in the study did not have significant weight loss.
The study's primary end point was the composite rate of death, nonfatal myocardial infarction, and nonfatal stroke. After a median follow-up of 46 months, the rate was identical in both diet groups, with a total of eight events in each group. In contrast, there were 40 events in the 101 patients in the control group (compared with a total of 16 among the 101 patients who began the two diet groups). The calculated odds ratio was a 67% risk reduction for patients in either diet group compared with control patients, a statistically significant difference, Dr. Tuttle said.
“We were surprised that there was no difference” between the two diets, she said in an interview. If the finding is confirmed, it would be good news for many American patients with coronary disease who don't like fish, she added. “These were mostly older, white patients in the U.S. Northwest, and a lot of them had trouble increasing their intake of fish and olive oil. They did, but they didn't like it.” Subsequent studies also need to test the hypothesis that it's the intensive intervention that's most important, and that any diet would be effective in this context, Dr. Tuttle said.