Monday, February 25, 2013

Latest Mediterranean Diet Study Results: Much Ado About Nothing

Olive oil
Fearing that it would have to write about the Oscar award show's vulgar Hollywood humor or Washington's budgetary caterwauling, the Disease Management Care Blog was happily distracted by a flurry of splashy news reports on a just-published primary prevention trial:

"Mediterranean diet....showed 30% lower risk of having a heart attack, stroke or dying of heart disease....."

"Tasty diet cuts heart disease, study finds."

" rich in olive oil, nuts, beans, fish, fruits and vegetables prevents about 30% of heart attacks, strokes and deaths from heart disease..."

Fighting the urge to run to the pantry and add years to its life by ingesting some olive oil-drizzled walnuts, the DMCB did something that mainstream news reporters seem incapable of doing: it asked what the diet actually entails and whether the impact was really all that.

Here's the original New England Journal of Medicine study. Disappointingly, the absolute risk reduction was quite small and, for the typical DMCB primary care patient, would involve a major lifestyle change.

The DMCB explains.

The PREDIMED trial ("Prevención con Dieta Mediterránea") was a prospective and randomized clinical trial in which male (age 55 to 80 years) and female (age 60 to 80 years) volunteers with either:

1) diabetes or

2) three other risk factors, such as tobacco use, high blood pressure, abnormal cholesterol levels, obesity and a worrisome family history of premature heart disease,

were randomly assigned to one of three treatment arms:

1) A "Mediterranean diet" supplemented with extra-virgin olive oil (a liter was delivered to the home each week), or

2) A "Mediterranean diet" supplemented with nuts (30 grams of almonds, walnuts and hazelnuts per day) or

3) A control diet.

What's just what is a Mediterranean diet?  According to the authors:

A) lots of olive oil for cooking and dressing dishes;

B) consumption of ≥ 2 daily servings of vegetables (at least one of them as fresh vegetables in a salad), discounting side dishes;

C) ≥ 2-3 daily servings of fresh fruits (including natural juices);

D) ≥ 3 weekly servings of "legumes" (kidney beans, pinto beans, black beans, chickpeas, lima beans, black-eyed peas, split peas, and lentils);

E) ≥ 3 weekly servings of fish or seafood (at least one serving of fatty fish);

F) ≥ 1 weekly serving of nuts or seeds;

G) selecting white meats (poultry without skin or rabbit) instead of red meats or processed meats such as burgers and sausages;

H) cooking regularly (at least twice a week) with tomato, garlic and onion adding or not other aromatic herbs, and dress vegetables, pasta, rice and other dishes with tomato, garlic and onion adding or not aromatic herbs. This sauce is made by slowly simmering the minced ingredients with abundant olive oil.

I) the limitation of cream, butter,margarine, cold meat, pate, duck, carbonated and/or sugared beverages, pastries, industrial bakery products (such as cakes, donuts, or cookies), industrial desserts (puddings, custard), French fries or potato chips, and out-of-home pre-cooked cakes and sweets.

By the way, the study organizers used genuine olive oil, not this fake stuff.

Patients assigned to the diet had to see a dietitian at the outset of the study and participate in every 3 month group education sessions.  There were no recommendations to lose weight or participate in exercise.

The results?

8713 persons were screened and 7447 were assigned to one of the study arms.  After a median of 4.8 years, 523 persons were lost to follow-up. 288 persons had either a heart attack, stroke or
cardiovascular death.  There were 96 deaths in the extra virgin olive oil group, 83 in the nut group and 109 in the control group. The calculated percents were 3.8%, 3.4% and 4.4%, respectively.  Versus the control group that's an absolute difference of 0.6% and 1.0%. There didn't appear to be any surprises in the subgroups' outcomes.

Using a number needed to treat analysis, these data basically mean 100 to 166 persons would need to live on fish, nuts, lima beans, and olive oil without burgers, starches or soda for 5 years to prevent a single heart attack, stroke or death.

The DMCB's take:

1. The small amount of benefit is not enough, in the DMCB's estimation, to warrant routine inclusion of a "Mediterranean diet" in disease management care planning for persons with diabetes or multiple cardiac risk factors.

2. The diet was "all or none."  There is no evidence, based on this trial, that substituting crab cakes for that steak once a week and using olive oil on your iceberg lettuce tonight will help you live longer.

3. The "number needed to treat" of 100-166 over 5 years is in the same performance range as statin drugs with a NNT that, according to this study, ranges from 77 to 150 over four years.  No wonder many persons choose to continue with their more tasty burgers and fries along with a daily pill.

4. It's unlikely that persons who are not already on a Mediterranean diet will chose to switch, and given the amount of sacrifice involved and the small reduction in risk, the DMCB can't blame them.

Image from Wikipedia


Marie said...

I agree that the study is much ado about nothing and I appreciate a blog that realistically criticizes it, something the mainstream media has failed to do. I would like to add though that the benefits of the mediteranean diet seem less impressive than even you indicate because there was no statistically significant difference in mortality, unless I misread their conclusion.

Jaan Sidorov said...

Marie is quite correct and I appreciate her important insight. I suspect the lack of a statistically significant difference in mortality was because that outcome was underpowered.

Thank you Marie! Well said, WELL said.