A snippet of a scene by the sea, a table full of dishes typical to the Mediterranean diet, chairs and foliage surrounding it.Share on Pinterest
When it comes to cardiovascular benefits, the Mediterranean diet is often named the best. Jimena Roquero/Stocksy
  • An analysis of diet trials concluded that a Mediterranean diet was best for overall cardiovascular health, followed closely by a low-fat diet.
  • The Mediterranean diet emphasizes fish, fruits, vegetables, and monounsaturated fats such as olive oil.
  • Researchers assessed seven diets: the Mediterranean diet, low-fat diets, very-low-fat diets, modified-fat diets, combined low-fat and low-sodium diets, and the Ornish and Pritikin diets.
  • A low-fat diet that also reduced sodium intake did not fare as well as a low-fat diet without salt reduction, potentially demonstrating the difficulties involved in conducting randomized, controlled trials such as those under review.

A new review of randomized, controlled trials finds that for people at risk of cardiovascular disease, the Mediterranean diet or a low-fat diet are the healthiest options.

The trials investigated the health benefits of seven diets: the Mediterranean diet, low-fat diets, very-low-fat diets, modified fat diets, combined low-fat and low-sodium diets, the Ornish diet, and the Pritikin diet, compared to not being on any particular diet at all.

The review found the Mediterranean diet reduced the likelihood of all-cause death, cardiovascular death, stroke, and non-fatal heart attacks.

Low-fat diets reduced the risk of all-cause mortality, non-fatal heart attacks, and unplanned cardiovascular interventions. The other diets showed no convincing evidence of increasing cardiovascular health, although a low-fat diet and low-sodium (salt) diet may be of benefit to people at high risk of stroke.

The 40 trials included in the review involved 35,548 participants who were followed for an average of three years from the start of trials. Adults who had cardiovascular disease, or who had two or more cardiovascular risk factors, were the primary focus of the review.

The study is published in The BMJ.

The Mediterranean and many low-fat diets involve an emphasis on vegetables and fruits. The Mediterranean diet also increases the intake of monounsaturated oils and fish.

“They’re largely the same,” said cardiologist Dr. Yu-Ming Ni, who was not involved in the study. They do have a few key differences, however.

“I would say that Mediterranean is a little bit more focused on lean protein and the use of olive oil and other vegetable oils in place of animal fats for cooking, and I think that emphasis is more helpful,” said Dr. Ni.

Dietician Kristin Kirkpatrick, who is also not involved in the study, said to assess whether one diet is healthier than another is “really dependent on the quality of the diet that the person is placing on it.”

“It’s important to look at the entire dietary quality rather than single nutrients like saturated versus unsaturated fats. There is no one-size-fits-all approach,” she said.

Kirkpatrick also generally favored the Mediterranean diet.

Dr. Ni, meanwhile, pointed out that “There are just a lot of low-fat diets out there that there are not a lot of specifics on,” and all are a little different from each other.

Dr. Ni noted that in this study—likely the largest study yet of the Mediterranean diet—the use of olive oil was associated with a significantly reduced risk of cardiovascular events.

Dr. Ni strongly recommended olive oil and avocado oil for cooking, and flax seed oil added on top of cooked foods.

Recognizing that these can be expensive ingredients, he said less expensive vegetable oils, such as soybean, canola, corn oil, and sunflower oil are “much better certainly than using butter, shortening, margarine, other types of synthetic oil, and things like that” when it comes to cardiovascular health.

One perhaps surprising finding in the study is that low-fat diets — which performed well overall — performed less well when they were combined with a reduction in sodium. There are two likely explanations for this.

Kirkpatrick cited other research which concluded that “reducing sodium may not be as beneficial as some think it is.”

According to that study, researchers found that sodium increased cardiovascular risk only for people consuming more than five grams a day. People with high blood pressure should ingest no more than one and a half grams of sodium a day, according to the U.S. National Institutes of Health.

That same study also found that increased potassium decreased the risk of cardiovascular disease.

This underscores, Kirkpatrick suggested, that “it’s important to think about dietary interventions holistically rather than focusing on single nutrient adjustments (or two nutrients) in this case.”

Dr. Ni agreed, saying:

“I think when you start to get into the details about specific elements of diet, you start to hit issues with confounding where certain dietary patterns might naturally be low in sodium, but higher in other aspects that are less healthy. And I don’t know that we can necessarily clarify that just with this kind of study.”

Dr. Ni said that there is only so much that can be expected from randomized diet trials. He cited the participants’ burden when taking part in a trial and the difficulties researchers have in getting them to remain committed to the process for extended periods.

“So, you know, we will never have very clear information on this. The best thing we can do is do these aggregates, where we take a lot of information from multiple studies and try to get a good idea of what’s going on,” Dr. Ni said.