For instance, a 'bad' fat such as saturated fat or trans fat, known to be damaging to cardiac health, was also linked to worse overall cognitive function and memory in women over time.
Conversely, a 'good' fat or mono-unsaturated fat was lined with better overall cognitive function and memory, the journal Annals of Neurology reported.
The research team from Brigham and Women's Hospital (BWH), analyzed data from the Women's Health Study-comprising nearly 40,000 women, 45 years and older. They focused on data from a subset of 6,000 women, aged over 65 years.
Women who consumed the highest amounts of saturated fat, which can come from 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 mono-unsaturated fats, found in olive oil, had better patterns of cognitive scores over time, said a university statement.
"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, psychiatrist from Brigham Hospital.
"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," added Okereke.