Even With No Restrictions on Fat Intake, Mediterranean Diet May Help Prevent Disease

People who eat a Mediterranean diet, even when there are no limits set on fat intake, seem to have a lower risk of cardiovascular events. They also are at lower risk of getting cancer or dying from it, authors of a new review and meta-analysis report.

The study, funded and conducted by the US Department of Veterans Affairs to determine whether the diet should be recommended in the clinical setting, highlights the role that monounsaturated fats such as olive oil and nuts play in limiting disease but doesn’t show any effect on all-cause mortality, according to Nieca Goldberg, MD (NYU Langone Medical Center, NY). Still, she stressed, the diet shouldn’t be dismissed.

"You don’t want people to think that it’s not beneficial to eat a Mediterranean diet,” Goldberg, who was not involved in the review, told TCTMD. “The traditional Mediterranean diet is probably higher in fat than the American diet, but with that said the fat content of the traditional Mediterranean diet is better in terms of the type of fats that are used like the omega-3 fats from fish, olive oil, and nuts."

Defining the Diet

In addition to unrestricted fat intake (with a high monounsaturated-to-saturated fat ratio), researchers led by Hanna Bloomfield, MD (Minneapolis VA Medical Center, MN), defined the Mediterranean diet as including high consumption of fruits, vegetables, whole grains, and fish as well as moderate levels of dairy and red wine plus low intake of meats.

In total, the investigators analyzed 90 papers on 56 studies with no fewer than 100 participants. All were published between 1990 and April 2016.

Two primary prevention trials showed no difference in all-cause mortality, though one found that a Mediterranean diet decreased the risk of major cardiovascular events by a relative 29%, breast cancer by 57%, and diabetes by 30%. Pooled analyses of cohort studies on primary prevention showed that people with the greatest adherence to a Mediterranean died had a 14% lower risk of dying from cancer, 4% lower risk of getting any type of cancer, and 9% lower risk of getting colorectal cancer than those with the lowest adherence.

Three secondary prevention studies reported cardiovascular outcomes, with just one demonstrating lower risk of recurrent MI and cardiovascular death among patients eating a Mediterranean diet.

Researchers said there was insufficient evidence for the outcomes of hypertension, kidney disease, and rheumatoid arthritis.

The Trials of the Diet

Beyond being limited by the small number of trials available to analyze the different diseases and outcomes, the review also highlights the difficulties inherent in researching the Mediterranean diet, according to Anthony Pearson, MD (St. Luke’s Hospital, Chesterfield, MO).

“I think that the big weakness of any research in this area is there isn't a clear-cut consensus definition” for what constitutes the Mediterranean diet, he told TCTMD. “It kind of comes from the early work of Ancel Keys based on what the diet was in Crete in Greece and other areas around the Mediterranean that showed a low cardiovascular risk. But exactly what that diet consisted of is kind of controversial, [and] exactly what components of it are important is not clear.”

Bloomfield also pointed to the consensus-lacking definition of the Mediterranean diet as a noteworthy problem for conducting research; this is underscored, she said, by the limited number of studies.

In addition, according to Pearson, the origins of the diet appear to be forgotten when studied in randomized controlled trials. “One of the things that drives me crazy is this idea that somehow low-fat dairy is a part of the Mediterranean diet, and obviously if we are talking about the way people ate around the Mediterranean in the 1950s and the 1960s, they were not pursuing low-fat or nonfat dairy,” he said. “Dairy is clearly not low-fat in this population, and there is nothing that would suggest that is a key component to the Mediterranean diet.”

Diet Still Worth Pursuing

Even with limited evidence for the diet’s benefits, physicians continue to recommend it to patients as one way to improve overall health. One key piece to this advice, though, is that it makes up only a small part of a person’s overall efforts to prevent disease. Another important element is making sure they know what goes into a Mediterranean diet in the first place.

“I recommend diets to patients as only one part of helping them reduce their risks for heart disease,” Goldberg told TCTMD. “A lot of people [in the United States] might think they are eating a Mediterranean diet, but actually they are eating too much saturated fat.” A key message, she said, is that a Mediterranean diet is “low in both meats and sweets.”

The health benefits of the diet are also apparent  in ways beyond the scope of research, according to Pearson, who said he recommends the diet to some of his patients. One of his main reasons is that it provides the opportunity for people to consciously make healthier choices and maintain those choices moving forward.

“The bottom line for me is that it is a reasonable diet,” Pearson concluded. “It has some scientific support in the literature. It’s sustainable. It’s interesting and diverse, and it’s something that they can live with for the rest of their lives.”

Michael H. Wilson is the 2016 recipient of the Jason Kahn Fellowship in Medical Journalism.

• Bloomfield HE, Koeller E, Greer N, et al. Effects on health outcomes of a Mediterranean diet with no restriction on fat intake: a systematic review and meta-analysis. Ann Intern Med. 2016;Epub ahead of print. 

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