It has been known for years that eating too many foods containing "bad" fats, such as saturated fats or trans fats, isn't healthy for your heart. However, according to new research from Brigham and Women's Hospital (BWH), one "bad" fat -- saturated fat -- was found to be associated with worse overall cognitive function and memory in women over time. By contrast, a "good" fat -- mono-unsaturated fat was associated with better overall cognitive function and memory.

This study is published online by Annals of Neurology, a journal of the American Neurological Association and Child Neurology Society, on May 18, 2012.

The research team analyzed data from the Women's Health Study -- originally a cohort of nearly 40,000 women, 45 years and older. The researchers focused on data from a subset of 6,000 women, all over the age of 65. The women participated in three cognitive function tests, which were spaced out every two years for an average testing span of four years. These women filled out very detailed food frequency surveys at the start of the Women's Health Study, prior to the cognitive testing.

"When looking at changes in cognitive function, what we found is that the total amount of fat intake did not really matter, but the type of fat did," explained Olivia Okereke, MD, MS, BWH Department of Psychiatry.

Women who consumed the highest amounts of saturated fat, which can come from animal fats such as red meat and butter, compared to those who consumed the lowest amounts, had worse overall cognition and memory over the four years of testing. Women who ate the most of the monounsaturated fats, which can be found in olive oil, had better patterns of cognitive scores over time.

"Our findings have significant public health implications," said Okereke. "Substituting in the good fat in place of the bad fat is a fairly simple dietary modification that could help prevent decline in memory."

Okereke notes that strategies to prevent cognitive decline in older people are particularly important. Even subtle declines in cognitive functioning can lead to higher risk of developing more serious problems, like dementia and Alzheimer disease.

This work was supported by research grants and awards from the National Institutes of Health (NIH)/National Heart Lung and Blood Institute (HL043851 and HL080467); NIH/National Cancer Institute (CA047988); and NIH/National Institute on Aging (AG015933 and K08 AG029813).