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We’ve talked a lot about diet studies here on 150 Seconds. I like to complain about them because most are observational.  People who eat healthy diets are healthier. Randomized trials are better, but unless you’re preparing every meal for the participant, you can never be 100% sure what they are getting.

Today we’re talking about a randomized diet trial that takes a somewhat unique approach to the issue.  In fact, I think the methodology in this study is more interesting than the results. In an article appearing in JAMA internal medicine, a group of Spanish researchers report on the relationship between a Mediterranean style diet and cognition in a group of around 450 individuals at higher risk of cardiovascular disease.

Mediterranean diets are characterized by fresh fruits and vegetables, fish, nuts, and olive oil. Micronutrient-wise, we’re basically talking about higher amounts of mono- and polyunsaturated fats, which, in the lab at least, seem to have antioxidant and anti-inflammatory properties.  In terms of cognitive decline, which may be partly a vascular process, tamping down these things could be beneficial.

There were 3 groups in the study.  A control “low-fat” diet group, and two Mediterranean diet groups: 1 supplemented with nuts, one with olive oil.  Here’s where it got interesting. The participants cooked all their own food - basically, the intervention was just some education and a weekly food “gift” of either 1 liter of olive oil or 1 cup of nuts.

Despite the lack of rigorous dietary control, the intervention groups did change their eating habits. Caloric intake didn’t change much, but carbohydrate intake went down and polyunsaturated fat intake went up in both mediterranean diet groups compared to the controls.

As for the primary results?  I wouldn't call them sizzling. Cognitive function declined a bit more in the control group than either of the Mediterranean diet groups, but changes were mild overall.

The trial itself had a few blemishes.  One is that, at first, the control group wasn’t treated very similarly to the intervention groups.  Controls had fewer visits, and didn’t get weekly “gifts” from the study.  This was remedied about halfway through the trial, but some damage had probably been done and it’s conceivable that controls who didn’t feel as invested in the study wouldn’t have performed as well on cognitive testing.

The second issue is a somewhat high dropout rate, around 25%, that was differential among the groups.  Neither of these are killer, but when you combine a couple of flaws like this with relatively mild results overall, you’re left wondering what to take home from this?

For me, it’s not the primary results. I’m just impressed that the simple act of giving people healthy food, giving people olive oil, changed their eating habits. That’s pretty slick if you ask me.