For the last 12 years, the answer has been “Mediterranean.” But a new study challenges that conclusion.
By the way, “diet” in this blog post refers to “a habitual way of eating” rather than a weight-loss program.
Researchers at The Heart Institute of Spokane (Washington) set out to compare the effects of a Mediterranean-style diet and a conventional “heart-healthy” low-fat diet in people who had suffered a heart attack within the last six months. To test whether diet intervention per se had any effect, a “usual-care” group of patients (101 participants) was also studied.
Dietary intervention participants were randomized to either:
- A low-fat diet (American Heart Association Step II) (50 participants). Main goals were to reduce cholesterol intake to under 200 mg/day and saturated fat to under 7% of total calories, or
- A Mediterranean-style diet (51 participants) with the same cholesterol and saturated fat goals, plus an increased intake of omega-3 fatty acids (to over 0.75% of calories) and monounsaturated fats (to 20-25% of calories). Emphasis was on consumption of cold-water fish 3-5 times per week, and on oils from olives, soybeans, and canola.
Both diets encouraged intake of fresh fruits and vegetables – at least 5 servings a day – and whole grains. Loss of excess weight was not a goal.
Diet intervention participants were given two individual counseling sessions with a dietitian within the first month, with additional sessions at months 3, 6, 12, 18, and 24. Participants also attended six group sessions. Three-day food diaries were examined periodically to assess compliance with dietary recommendations. Various lipids and omega-3 fatty acids were measured in plasma. I assume that judicious wine consumption was at least mentioned as part of the Mediterranean diet, but actual intake was not reported.
The “usual-care” group, also known as controls, “received dietary advice from medical center dietitians. American Heart Association Step II guidelines were presented as a nutrition class or video and written materials.” Just one presentation, apparently.
All participants were followed on average for almost four years. “The primary outcome [emphasis added] was a composite of end points including all-cause and cardiac deaths, myocardial infarction, hospital admission for heart failure, unstable angina, or stroke.” Obviously, you want to avoid these primary outcome end points.
- Avoidance of the primary outcome end points was the same in both the low-fat and Mediterranean diet groups. Each intervention group had eight primary outcome end points.
- Forty of the 101 people in the usual care group suffered one or more of the primary outcome end points. Only 16 of the 101 dietary intervention patients suffered one or more of the primary outcome end points. Compared to the usual care group, the dietary intervention patients were only one-third as likely to suffer cardiac death, death from any cause, heart attack, hospital admission for heart failure, unstabe angina, or stroke. This is a significant difference.
- Goals for cholesterol, saturated fat, and omega-3 intake were achieved, or nearly so, in the dietary intervention groups.
- Neither diet intervention group lost weight.
- After two years, there were no differences between low-fat and Mediterranean groups in terms of HDL cholesterol, LDL cholesterol, triglycerides, and fasting glucose.
- Among the diabetics (10 in each intervention group), there were no differences in fasting glucose.
- The drop-out rate was low.
In the researchers’ words:
[This study] demonstrates that low-fat and Mediterranean-style diets can be similarly effective strategies for therapeutic lifestyle change, particularly when applied with equal intensity of intervention.
[This study] highlights the importance of heart-healthy diets in patients who have recently had [heart attacks]. The 2 intervention groups had relatively low intakes of cholesterol and saturated fat, but only Mediterranean-style diet partipants increased omega-3 fat consumption. Because neither cardiovascular events nor risk factors differed between interventions , [this study] does not substantiate claims that increased omega-3 fat intake, predominantly from eating fish, adds benefit beyond a diet emphasizing reduced cholesterol and saturated fat.
The authors admit that the small number of participants is a weakness of their study.
They also cite another study, Medi-RIVAGE, that tends to support their findings. Yet the Medi-RIVAGE “data predicted a 9% reduction in cardiovascular disease risk with the low-fat diet and a 15% reduction with this particular Mediterranean diet.” According to the Medi-RIVAGE study abstract, “After a 3-mo intervention, both diets [low-fat and Mediterranean] significantly reduced cardiovascular disease risk factors to an overall comparable extent.”
The seeming equality of the low-fat and Mediterranean diets is a surprise to me. I would have predicted superiority of the Mediterranean diet. Alcohol and nut consumption have been associated with improved cardiovascular outcomes in several observational studies. I wonder if these two intervention groups had the same or different consumption of alcohol and nuts.
But these researchers may be on to something here. That is, low-fat and Mediterranean diets – with intensive dietary instruction – are equally good diet interventions for preventing future cardiac events in people who have had a recent heart attack. Dr. Dean Ornish’s vegetarian program might also stack up well against these two diets and “usual care.”
Before I abandon my preference for the Mediterranean diet in prevention of cardiac disease, I’d like to see the findings of this study confirmed by a larger one. In addition to cardiovascular benefits, the Mediterranean diet is associated with:
- longer life span
- reduced incidence of cancer
- reduced incidence of dementia
- reduced incidence of chronic obstructive pulmonary disease
- improved control of asthma
- prevention of type 2 diabetes mellitus
No diet other than the Mediterranean can legitimately claim all these benefits. And it tastes good.
Steve Parker, M.D.
Tuttle, Katherine R., et al. Comparison of Low-Fat Versus Mediterranean-Style Dietary Intervention After First Myocardial Infarction (from The Heart Institute of Spokane Diet Intervention and Evaluation Trial). American Journal of Cardiology, 101 (2008): 1,532-1,531.
Vincent-Baudry, Stephanie, et al. The Medi-RIVAGE study: reduction of cardiovascular disease risk factors after a 3-mo intervention with a Mediterranean-type diet or a low-fat diet. American Journal of Clinical Nutrition, 82 (2005): 964-971.