The good, the bad and the ugly: New research about the fat in food and what it may mean to your health.

Experts know that saturated fat, the stuff found in red meat and full-fat dairy food, isn’t your friend and can contribute to clogged arteries. Monounsaturated fat, like in olive oil, has a healthier reputation. Now, a new study from the journal Annals of Neurology finds that these fats may play good and bad roles in your brain too.

Researchers asked more than 6,000 older women about their diet, then gave them several tests on their mental function over the course of four years. Women who ate more saturated fat saw their mental abilities decline more over time. The women who ate more monounsaturated fat, however, aged better in terms of their thinking and memory.

These findings may add even more support to the Mediterranean Diet, which relies heavily on olive oil as a source of fat.