Your Brain On Butter: The Fats That May Hasten Mental Decline

What's good for the heart is good for the brain, the medical thinking goes.

Here's the latest twist: What's bad for the heart turns out to be bad for the brain. Put another way, some fats may make us stupider — or at least less cognitively on the ball.

Amid growing evidence that what we eat has a profound impact on brain function, researchers at Brigham and Women's Hospital in Boston found that women who consumed the highest amounts of saturated fat — which can come from animal fats like red meat and butter — had worse overall cognitive function and memory over four years of testing compared to women who ate the lowest amounts of such fats. Moreover, women who consumed the most monounsaturated fats — think olive oil — scored better on the cognitive function tests over time.

(Trans-fats found in processed and baked goods — like those ginormous muffins they used to sell at the corner deli — are also considered "bad" but in this particular study, they weren't associated with declines in cognitive ability.)

To be clear, this latest research doesn't mean that if you start cooking with olive oil instead of butter you'll suddenly be able to locate your car keys or remember your mother-in-law's birthday.

But it does strongly suggest that the type of fat you eat matters,

and overall, certain so-called bad fats can undermine all kinds of cognitive function as well as short and long-term memory as you age, says Dr. Olivia Okereke, the study's lead author and a psychiatrist at Brigham and Women's. The research, which evaluated 6,000 women over 65, a subset of the larger Women's Health Study, was published online in the medical journal Annals of Neurology.

Okereke said in an interview that the findings have significant public health implications and a fairly straightforward take-home message: "If people substitute out portions of saturated fat and replace it with the same amounts of monounsaturated fat, like substituting olive oil in place of butter," she said, "it's a simple dietary modification that could prevent decline in memory."

She cited earlier research that suggests even slight declines in cognitive functioning can lead to a higher risk of developing more serious problems, like full-blown dementia or Alzheimer's disease.

This study didn't look at why bad fat might chip away at cognitive function as we age. Okereke theorized that bad fats might be linked to inflammation or changes in lipid profiles. But she said the precise mechanism that connects saturated fat consumption with brain function requires further study. "It's long been known that overall cardiovascular health is good for cognitive function," she said, "So it makes sense that the same factors that are good for cardiovascular health would also be good for cognitive function."

Researchers involved in a study published earlier this year that found cognitive decline might began as early as age 45, reiterated that heart health and brain health go hand in hand. Dr. Frances Grodstein, an associate professor of medicine at Brigham and Women’s who studies aging and was also involved in the latest dietary fat study, told CommonHealth: "A simple way to think about it is that cardiovascular disease and brain health really seem to share a lot of risk factors. So most of the things we think about in terms of heart health probably work for brain health as well: Diet, exercise, things people have been telling you about for years."

In the latest dietary fat study, cognitive function was measured in several ways, including tests of attention, list learning, evaluating short and long-term memory and so-called category fluency, in which subjects are asked, for instance, to list as many animals as possible in one minute. Researchers combined the results of all the tests to get a picture of what overall cognitive function looks like.

Asked if the findings might change the way she practices medicine, or her own personal diet, Okereke said health care providers — including mental health specialists — should consider initiating conversations with patients about the differences and potential impacts of various fats. "I would say it has definitely enlightened me about the potential importance of these types of fats," she said. "It's very enlightening."