In a finding sure to fuel the debate over the harms of saturated fat, researchers at Brigham and Women’s Hospital published a study Friday suggesting that saturated fats — found in red meat and full-fat dairy products — causes the brain to age more rapidly than other kinds of fat. Olive oil, avocado, and other monounsaturated fats appear to slow brain aging.

The study, published online in the Annals of Neurology, compared dietary surveys taken from nearly 6,200 healthy women over age 65 with cognitive functioning tests taken about five years later and found that those women who reported the highest saturated fat intake also had, on average, the worst scores on reasoning and memory tests. Those with the highest monounsaturated fat intake had the best cognition test scores on average, compared with those who ate mostly polyunsaturated fats — found in corn and vegetable oils.


Women who had a high intake of saturated fat had brains that appeared 5 or 6 years older than their biological age, according to study author Dr. Olivia Okereke, a psychiatrist and epidemiologist at the Brigham, while those with the highest consumption of monounsaturated fat had brains that were about 6 or 7 years younger.

“In general, when it comes to dietary fat, the message has been pretty consistent over time that those dietary fats that are beneficial for cardiovascular health might similarly be beneficial for brain health,’’ said Okereke. Saturated fats are thought to promote inflammation and damage to the arteries.

Total fat intake didn’t appear to have an effect on brain aging, nor did polyunsaturated fats. Oddly, trans fats — which are thought to be even more harmful than saturated fats — were not associated with accelerated cognitive decline in this particular study; they have, though, been implicated in other studies. Okereke said this discrepancy could be due to a low trans fat intake among study participants in her study.

Like most nutrition studies, this one can’t prove that dietary fat has a direct effect on brain function because it didn’t randomly assign women one diet or the other to follow. While the researchers accounted for differences in body weight, smoking, alcohol use, and certain health conditions such as diabetes and hypertension, they couldn’t look at all potential differences between those who ate high amounts of saturated fats compared with those who ate more monounsaturated fats. For example, the study didn’t look at total fruit or vegetable consumption.


That said, enough evidence has accumulated from a host of dietary studies to suggest that it’s wise to limit your intake of saturated fat, opting instead for healthier monounsaturated fats.

“Our analysis suggests if you substitute out 5 percent of your saturated fat calories with 5 percent monounsaturated fats, you could have a 50 percent lower risk,’’ said Okereke, of having an accelerated decline in your memory and other cognitive functions as you age.

Something as simple as replacing a pat of butter on your bread with a drizzle of olive oil could help protect your brain health over the long haul.