Karen Weintraub, Special to USA TODAY

Yet another reason to cut back on cookies: A new study shows that eating trans fat – used for decades in margarine and to increase the shelf life of packaged cookies and crackers – may damage memory.

Of 690 young and middle-aged men tested, those who reported eating the most trans fat, also called partially hydrogenated oil, remembered 11 fewer words out of 104 than those who ate the least, according to the study presented today at the American Heart Association conference in Chicago.

"Trans fats increase the shelf life of the food but reduce the shelf life of the person," said the study's author, Dr. Beatrice Golomb, a professor at the University of California, San Diego School of Medicine. Other research has shown a link between trans fat consumption and obesity, aggression, heart disease and diabetes.

"They're a metabolic poison and that's not a good thing to be putting into your body," she said. "They don't provide anything the body needs."

Golomb, said she decided to research trans fats when she realized that they had the opposite effects on the body as chocolate, which she had previously shown to be healthy.

The study also adds to the growing body of evidence that what we eat affects how we think, said Dr. Patrick T. O'Gara, president of the American College of Cardiology. "The supply of nutrients in blood to the brain can actually affect its function."

Although the cause-and-effect hasn't been proven and it's not entirely clear why eating trans fat would cause memory loss, several experts said they think the finding makes sense.

"These artificial fats penetrate every cell in the body and can disrupt basic cell functions," said Dr. Walter Willett, chairman of the Department of Nutrition at the Harvard School of Public Health, who was not involved in the research.

The amount of trans fat in the food supply has been cut drastically since 2006 when manufacturers were required to list trans fats on labels. Most margarine, for instance, no longer contains trans fats, and many companies have reformulated their baked goods without the partially hydrogenated vegetable oils that used to allow them to sit on shelves for months without rotting.

The benefits are already obvious, Willett said via e-mail. "Heart disease is declining more rapidly in areas where trans fats have been banned [like Boston] and trans fat reduction is almost surely contributing to recent declines in diabetes incidence in the US."

But the government still allows any product with less than half a gram of trans fat to be labeled as trans fat-free. Products that contain trans fats will mention on the ingredient list something that is "partially hydrogenated." A quick check of Keebler products on Keebler.com, for instance, revealed that 42 out of about 100 products list partially hydrogenated oils among their ingredients, but were labeled as having no trans fats.

Willett said he doesn't know of any way to reverse the impact of trans fats on the body and brain, other than living as healthy a lifestyle as possible going forward, including getting regular exercise, not smoking, maintaining a healthy weight, limiting alcohol, using liquid vegetable oils instead of hard fats when possible, and consuming a heart healthy diet including lots of fruits and vegetables.