To come up with their findings, Golomb and her team showed a series of cards bearing single words to 1,000 men who were asked to note repetition in the words on subsequent cards. The more trans fat the men had in their diets (based on retrospective surveys), the more poorly they performed on the memory test.

Of course, those diet surveys relied on memory. And other foods might have been causing this association. Could it be that people who eat diets that are high in trans fats are also eating diets that are overall terrible? High in things like sugar or pesticides or plastics or tilapia? Yes, it could. The study accounted for variables like education and depression, which might influence memory—but it didn't account for the rest of what the people eat. It actually only accounted for one other dietary variable outside of trans fats: chocolate.

Why chocolate? Why, chocolate?

Because, Golomb told me, chocolate intake seems to have a link to memory. Her own research has actually shown it. In addition to a 2012 finding that people who eat chocolate more frequently tend to have lower body-mass indices, Golomb has also found that people who eat a lot of chocolate tend to perform better on memory tests.

(Eating omega-3 fats might also improve memory, Golomb told me—something I mentioned in "This Is Your Brain on Fish"—but her current study didn't account for omega-3s.)

The idea is that chocolate has antioxidant effects which improve the functioning of cells that line blood vessels, leading to better blood flow and cell energy, which in turn improves cognition. And Golomb is not alone in championing that idea. The New England Journal of Medicine recently published a novel study that found "a surprisingly powerful correlation between chocolate intake per capita and the number of Nobel laureates in various countries."

Chocolate Consumption and Nobel Laureates

Franz Messerli, a professor of medicine at Columbia University, noted in that study that flavonoids, which are abundant in plant-based diets, have been shown to improve cognitive function. "Specifically, a reduction in the risk of dementia, enhanced performance on some cognitive tests, and improved cognitive function in elderly patients with mild impairment have been associated with a regular intake of flavonoids," wrote Messerli in the journal article. The subclass of flavonoids called flavanols, which are in cocoa, green tea, and red wine, "seems to be effective in slowing down or even reversing the reductions in cognitive performance that occur with aging."

Another study, released last month, found that people who drank a mixture loaded with cocoa flavanols did better on a memory test than people who drank a low-flavanol mix. The older subjects performed at the same level as people two to three decades younger.