You already know that trans fats, those pesky partially hydrogenated vegetable oils found in many processed foods, are detrimental to your heart and waistline. But new research suggests they may also damage your brain.

In a study published in the journal Neurology, elderly people with high trans fats levels in their blood not only performed poorly on memory tests, but also had smaller brains—a hallmark of Alzheimer’s disease.

In contrast, people who had high amounts of omega-3 essential fatty acids and vitamins B, C, D, and E in their blood had larger brains.