By Michael Yudell
Results of an important study out of Spain published last week in the prestigious New England Journal of Medicine suggests that a “Mediterranean Diet” supplemented by additional extra-virgin olive oil or nuts significantly lowered the risk of having a heart attack, stroke, or dying from heart disease.
But despite the media brouhaha—headlines like “Tasty Diet Curbs Heart Disease, Study Finds” and “Mediterranean Diet Study Rocks the Medical World”— the study's implications for you and me are still unclear.
Don’t get me wrong. This is a valuable study, the largest of its kind to date. And it confirms earlier research showing that the Mediterranean Diet — a high intake of olive oil, nuts, vegetables, and cereals; moderate consumption of fish and chicken; low consumption of dairy, red and processed meats, and sweets; and drinking wine in moderation with meals — can be effective in moderating cardiovascular risks.
Here’s what the researchers in Barcelona did: they enrolled 7,447 people between the ages of 55 and 80 with no history of heart disease but at risk for it. Risks included either type 2 diabetes or at least three of the following major risk factors: smoking, hypertension, elevated or low low-density lipoprotein cholesterol levels, overweight (or obesity), and a family history of premature coronary artery disease.
Participants were then randomly assigned into one of three dietary intervention groups: a Mediterranean Diet supplemented with extra-virgin olive oil (participants were given 1 liter of oil per week), a Mediterranean Diet supplemented with nuts (participants were given 15 grams of walnuts, 7.5 grams of hazelnuts, and 7.5 grams of almonds per week), or a low-fat diet (participants were not given any food supplements). The recommended low-fat diet called for at least three servings per day each of lean fish and seafood, low-fat dairy products, breads, potatoes, pastas and rice, fruits, and vegetables. The consumption of vegetable oils (including olive oil), sweets, nuts and fried snacks, red and processed meats, visible fat in meats and soups, fatty fish, spread fats, and sofrito were all discouraged.
Participants in the two Mediterranean Diet groups met quarterly with dietary screeners to determine adherence to their diets, while those in the low-fat group received yearly leaflets explaining how to stick to their diet. To evaluate adherence to the diets, Mediterranean dieters had their blood and urine tested for “biomarkers of compliance” —urine levels of hydroxytyrosol (olive oil byproduct) and plasma levels of alpha-linolenic acid (a nut byproduct). No such biomarkers were measured in the low-fat group.
Three years into the study the investigators realized, however, that the disparity in oversight between the Mediterranean and the low-fat groups was potentially biasing the study against the low-fat dieters. Thereafter, the study was changed to offer the same quarterly meetings and advice that the Mediterranean dieters had been getting.
The trial was stopped early, after nearly five years, when researchers found that the Mediterranean Dieters, supplemented with either extra-virgin olive oil or nuts, already had a “a substantial reduction in the risk of major cardiovascular events” (about 30%) that researchers believed was a result of their dietary changes.
So far so good, right?
Well, mostly. Study results seem to confirm what smaller studies have already shown —that there is a likely benefit to cardiovascular health from the Mediterranean Diet.
But the study’s shortcomings and the media’s promotion of its findings as an amazing new tool in the arsenal against heart disease should give us pause.
Here are a few important issues to consider (some of which the researchers acknowledge):
- The initial gap in diet oversight between the two Mediterranean groups and the low-fat t group might have biased the findings against the low-fat dieters.
- Individuals who dropped out of the study tended to have worse risks for cardiovascular disease than those who stayed in the study, which could have exaggerated the overall benefit of the Mediterranean diet.
- All study participants already lived in a Mediterranean country and were already at high cardiovascular risk. This limits what epidemiologists call the “generalizability” of the study. Since most of us neither live in a Mediterranean country nor are at high risk for cardiovascular disease, we do not know how, for example, Philadelphians at low risk for cardiovascular disease – in other words, most people around here – would do in such a study.
- We do not know how individuals in non-Mediterranean countries would adapt to the diet, or whether most of us could even afford it. Access to fish and olive oil can be expensive, and in this study the researchers provided the olive oil for free.
- Already living in a Mediterranean country, individuals assigned to the low-fat group may have already been eating a Mediterranean diet and had to change it to a low-fat one, while individuals in the two Mediterranean groups may have had their standard diets supported by the study and supplemented by the extra oil and nuts.
Another issue to consider, as Larry Husten at Forbes.com points out, is whether “we’ve made this issue far too complex.” “Instead of getting lost in the weeds hunting for clues to a metabolic mystery,” Husten posits, “perhaps we should think about diet more simply as a public health issue. Make healthy foods available to people. If people substitute walnuts or olive oil for a candy bar or French fries then they will benefit.”
One final thought: the role that the media plays in the popularization of “life changing” studies, like the Mediterranean Diet study, is often counterproductive. When a study like this is published and unleashes a media torrent, the public may uncritically embrace the findings, only to eventually find out that the headlines did not match the research. When this happens, the public can grow weary, even cynical, of such claims.
Is there a better approach for translating scientific studies for popular consumption?
In my own work looking at the popularization of autism science research, my collaborators and I have recommended that scientists receive better media training to improve the translation of their work to the public. That includes scientists working more closely with their university press offices to more accurately portray their work. This is a concern, because as one study found, “press releases from academic medical centers often promote research that has uncertain relevance to human health and do not provide key facts or acknowledge important limitations.”
It may as yet be premature to invest your kid’s college savings in Don’s House O’Nuts or in olive oil futures. But science is a process, moving forward in fits and starts as it expands our understanding of the world around us and of ourselves. We don’t need to oversell scientific discoveries — they shouldn’t be sensationalized. Science is cool enough, and in the case of the Mediterranean Diet, tasty enough to withstand the rigors of discovery without the hype.
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