Digging deeper into the New England Journal of Medicine Mediterranean Diet Study 0

The recent New England Journal of Medicine Study, “Primary Prevention of Cardiovascular Disease with a Mediterranean Diet” from April 2013 showed an inverse relationship between adherence to the Mediterranean Diet and cardiovascular health. Simply stated, the study concludes that a Mediterranean Diet supplemented with olive oil and nuts reduces cardiovascular events.

This may sound like a promising green light to go ahead and eat all things “Mediterranean,” but based on my last post, “Mediterranean diet myths debunked!” I thought it might be worthwhile to dig a little deeper into the study’s actual data to see if there really is a proven inverse relationship between the Mediterranean Diet and cardiovascular events.

Who were the study participants?

Here is the patient profile:

  • Eligible participants were men (55 to 80 years of age) and women (60 to 80 years of age) with no cardiovascular disease at enrollment but who met one of the two requirements below:
    1. Had type 2 diabetes mellitus OR
    2. Had at least three of the following major risk factors:
      • smoking
      • hypertension
      • elevated low-density lipoprotein cholesterol levels
      • low high-density lipoprotein cholesterol levels
      • overweight or obesity
      • family history of premature coronary heart disease

To put these characteristics into a more practical context, these participants suffered from metabolic syndrome, but they had not yet experienced a cardiovascular event or cardiovascular disease.

What diets were tested? 

The participants were assigned to one of three diets:

  1. Mediterranean Diet supplemented with extra-virgin olive oil
  2. Mediterranean Diet supplemented with mixed nuts
  3. Control Diet (a “low fat” diet)

The complete dietary guidelines for the three groups can be found in Table 1 in the study.

I realize that it can be challenging to design a perfect study, but it would have been especially helpful to include two additional participant groups: A Standard American Diet group and a Plant-based diet group.

Let’s take a closer look at the data

As we dig a bit deeper into the actual data, you’ll see that the Mediterranean Diet participants experienced no significant reduction in heart attacks, death from cardiovascular causes or death from any cause. The only statistically significant reduction for the Mediterranean Diet participants was “death from stroke,” thus resulting in an overall reduction in cardiovascular events (as the primary endpoint was a composite of myocardial infarction, stroke, and death from cardiovascular causes).  The Mediterranean Diet participants had a slight edge over the control group, showing 0.18% fewer deaths from stroke compared to the control group.

The control group’s “low fat diet” wasn’t exactly low in fat

Total fat consumption in the control group only decreased from 39% to 37% (based on calories) during the time the study was conducted. This percentage of fat is actually quite a bit higher than the American Heart Association’s guidelines for a low-fat diet (< 30% fat). Many health professionals in the plant-based field would argue for an even lower percentage (likely around 10%) in order to prevent and reverse heart disease.

Since not all fats are created equal, it would be especially important to see the breakdown of the types of fats consumed by the participant groups. How much saturated fat were the different groups consuming? This might help us to paint a more complete picture of the study results. One of the key differences between the control group’s Low Fat Diet and the Mediterranean Diets is the incorporation of low-fat dairy in the control group’s diet. Control group participants were advised to consumer ≥3 servings/day of low-fat dairy products. While the control group’s diet may be labeled as low fat, it’s not necessarily lower in saturated fat. In fact, 3 servings of low-fat dairy products can have as much if not more saturated fat than a 3 ounce serving of beef.

Does counseling impact behavioral change?

Lastly, in looking beyond the numbers, there is one final qualitative component to consider. From a behavioral standpoint, it’s important to note that for 3 of the 4.8 years of the study, the control group received no counseling whereas the Mediterranean Diets participants received quarterly counseling sessions for the duration of the study. In October 2006, 3 years into the trial, the lead researchers determined that this difference was a potential weakness of the trial. They amended the protocol to include quarterly individual and group sessions with delivery of food descriptions, shopping lists, meal plans and recipes. It’s impossible to know if equitable counseling from day one would have impacted the control group’s behavior, but counseling, whether individual or group, has been shown to positively impact health, diet and lifestyle decisions.