A new study gives us yet another reason to ditch the junk food. A study conducted at the University of New South Wales (UNSW) found that a diet high in fat and sugar can take its toll on cognitive abilities in as little as a week, and the effects may be permanent.

The UNSW news release explains that rats were fed one of three diets: a “cafeteria diet,” which was high in fat and sugar; a healthy diet; or a “healthy with sugar” diet which was healthy with the addition of sugar water.

The study found that rats fed a cafeteria diet had a reduced ability to recognize when an object was shifted to a new location, as compared to rats fed a healthy diet. Researchers noted that rats had similarly impaired memories when fed a healthy diet with sugar.

Researchers say the unhealthy diet led to inflammation of the hippocampal region of the brain, which plays a role in one’s spatial memory.

We know that obesity causes inflammation in the body, but we didn’t realize until recently that it also causes changes in the brain,” said Margaret Morris, a professor at UNSW School of Medical Sciences and one of the study’s authors.

What is so surprising about this research is the speed with which the deterioration of the cognition occurred,” she said. In fact, cognitive abilities were diminished even before the rats showed changes in weight.

Professor Morris added, “Our preliminary data also suggests that the damage is not reversed when the rats are switched back to a healthy diet, which is very concerning.”

She said these findings could have the biggest implications for older individuals. “An elderly person with poor diet may be more likely to have problems,” she said, and a healthy diet may be able to help prevent cognitive decline.

There is a small silver lining: not every aspect of memory was harmed by an unhealthy diet. Regardless of the type of diet, the rats were equally able to recognize objects.

The full study appears in the UNSW journal, Brain, Behavior and Immunity.