A Closer Look at Recent Study on the Mediterranean Diet

R. James Barnard, Ph.D. UCLA Distinguished Professor Emeritus, Department of Integrative Biology and PhysiologyRonald Scheib, M.D. Medical Director, Pritikin Longevity Center
Kimberly Gomer, M.S., R.D.

Media excitement over a recent study on the Mediterranean diet may have led some to believe that olive oil and nuts will save them from heart disease. Here’s a closer look at the study by doctors and dietitians at UCLA and the Pritikin Longevity Center.

We’ll start by talking about what’s good about this study,* which garnered headlines like “Mediterranean Diet Shown To Ward Off Heart Attack and Stroke.”

The study affirmed the benefits of a healthy diet even for people already taking medications for high cholesterol, blood pressure, or diabetes.

The takeaway: Drugs have benefits. Drugs plus diet have even more benefits.

And there’s no question that a Mediterranean-style diet (fruits, vegetables, legumes, fish, whole grains, nuts, olive oil, wine) is healthier than a typically American diet, full of fast food and other artery-cloggers like cheese, butter, red meat, processed meats, refined flour, sugar, and salt.

Now to the problems (and there are many) with this study. We’ll focus on three major ones.

• The study followed 7,447 people with heart disease risks who were randomly assigned to either Mediterranean-style diets or a low-fat diet, but the low-fat diet was not low in fat. Not even close. The people in the “low-fat” group started out with a diet that was 39% fat. They decreased fat intake to 37%.So, the authors weren’t really comparing a Mediterranean diet to a low-fat diet. It’s much more accurate to say they were comparing a Mediterranean diet to a typical American-style diet. And sure enough, a lot of the foods the so-called “low-fat” group was eating were heart-damaging foods like red meat, commercially baked goods full of refined flour and fat, sugary sodas, and low-fat cheeses. (Though called “low-fat,” these cheeses typically get 35 to 60% of their calories from fat.)
• Some argued that the people in the “low-fat” group were unsuccessful in reducing their fat intake because a low-fat diet is too difficult to maintain, but it could also be argued that the scientists conducting this study never really gave the “low-fat” diet group much of a chance. During the first half of the study, the people assigned to the Mediterranean diet received intensive education in eating well, including regular visits with registered dietitians. The people in the “low-fat” group got just one visit. That’s it. It was the equivalent of a doctor’s visit in which the doctor hands you a pamphlet with what to eat, and what not to eat, and essentially says, “Good luck.”Moreover, the “low-fat” diet that the scientists designed excluded an important food proven to protect against heart disease, a food that is a part of many low-fat plans, including the Pritikin Program – omega 3-rich fatty fish. The subjects in the study were discouraged from eating fatty fish like salmon.And ironically, this “low-fat” diet devised by the scientists had no limits on some foods known to increase heart disease risk, like soft drinks.
• The scientists summarized that the Mediterranean diet “reduced the incidence of major cardiovascular events” compared to a low-fat diet, and media articles led with announcements like “30% of heart attacks, strokes, and deaths from heart disease were prevented.”But in the study itself, the scientists reported no significant reductions in heart attacks or cardiovascular-related deaths among the Mediterranean dieters. They wrote, “Only the comparison of stroke risk reached statistical significance.”So how did they jump from stroke reductions to all reductions in cardiovascular risk? Well, it’s easy when you know how to play with numbers. They pooled all the data on heart attacks, strokes, and deaths, and the numbers on strokes were high enough so that the average of the three looked good.

Bottom Line: It appears that the scientists were doing everything they could to make the Mediterranean diet the winner, and the low-fat diet the loser. Why? We don’t know for sure, but consider this:

The olive oil, nut, and wine/alcohol industries were very involved in this study. Two olive oil companies supplied all the olive oil. Two nut companies supplied all the nuts. The lead author, Dr. Ramon Estruch, has served on the board and received lecture fees from wine groups like the Research Foundation on Wine and Nutrition and the European Foundation for Alcohol Research.

The other authors of the study have deep ties with other olive oil, nut, and wine groups such as the California Walnut Commission, the International Nut and Dried Fruit Council, the Mediterranean Diet Foundation, and a wine/alcohol public relations group in Spain called Cerveceros de España.

Yes, these scientists may have had a vested interest in making the Mediterranean diet look as good as it possibly could. By contrast, there was no financial interest in making the “low-fat” diet look good.

Given our national epidemics of obesity, heart disease, diabetes, and hypertension – and the staggering costs of these conditions – it is vital that the scientific community give all promising dietary plans a fair shake, particularly well-constructed ones with proven track records like the Pritikin Program. So strong are the data affirming the heart-healthy benefits of Pritikin that Medicare is now covering it for people with a history of cardiovascular disease.

Healthful low-fat plans include all the excellent elements of a Mediterranean diet (fruits, vegetables, whole grains, legumes, fish) and the ability to shed excess weight (something the subjects in the Mediterranean study did not achieve) because calorie-dense foods like oil and nuts are kept to a minimum.

As a nation, we have a real opportunity over the next several years to grow in our understanding of dietary/lifestyle interventions and their extraordinary benefits. Let’s make sure that scientific research rigorously and uniformly reviews all promising approaches, not just those with hefty backing from the olive oil, nut, and alcohol industries.

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A closer look at a key table in the Mediterranean diet study, by Jay Kenney, PhD, RD, Nutrition Research Specialist and Educator at the Pritikin Longevity Center

The table below, published in the study, shows the deaths from cardiovascular disease as well as total deaths in people following three diets: the Mediterranean Diet with EVOO (extra virgin olive oil), the Mediterranean Diet with nuts, and the Control Diet (the so-called “low-fat” diet). There were about 2,500 people in each group.

About one-third of the way down the table, you can see that during the five-year follow-up the Mediterranean/olive oil group had 26 deaths attributed to cardiovascular causes, the Mediterranean/nut group experienced 31 deaths from cardiovascular causes, and the questionable “low-fat” group had 30 deaths from cardiovascular causes. None of these differences was statistically significant.

Moreover, the total deaths from all causes in the Mediterranean/olive oil, Mediterranean/nut, and “low-fat” groups were 118, 116, and 114, respectively. Obviously, these differences are also statistically insignificant, but interestingly, the fewest absolute number of deaths actually occurred in people assigned to the “low-fat” group!

A close analysis of this table, as we have just done, might well make people wonder why this study got so much favorable press.

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* New England Journal of Medicine, February 25, 2013; DOI: 10.1056/NEJMoa1200303

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