By Mike Pomranz
Updated September 21, 2015
© Larry Lilac / Alamy

We are fairly certain that an unhealthy diet can affect how you look: a larger waistline, maybe an extra chin, that glazed-over stare you get after eating 11 tacos in one sitting. But new research suggests that an unhealthy diet can also affect how you think by literally reducing the size of part of your brain.

A study by researchers at Australia’s Deakin University and the Australian National University (ANU) that was recently published in BMC Medicine has found a connection between unhealthy “Western” dietary patterns and a smaller left hippocampus—a part of the brain responsible for things like learning, memory and mental health. The researchers, who looked at MRI images of the brain taken from Australian participants ages 60 to 64 years, in a large longitudinal study conducted by the ANU, tried to account for all other outside factors besides diet and still found that, within this population of older Australians, the people who ate a more nutrient-rich diet had a larger left hippocampal volume. “To our knowledge, this is the first human study to demonstrate associations between diet and hippocampal volume concordant with data previously observed in animal models,” the team wrote in their conclusion.

“It is becoming even clearer that diet is critically important to mental as well as physical health throughout life,” said Felice Jacka, an associate professor at Deakin University and the lead author of the study. “We’ve known for some time that components of diet, both healthy and unhealthy, have a rapid impact on aspects of the brain that affect hippocampal size and function, but up until now these studies have only been done in rats and mice.”

So what exactly constitutes an unhealthy diet compared to a healthy diet? According to their paper, the researchers defined a “prudent” diet as one “characterized by the consumption of fresh vegetables, salad, fruit and grilled fish.” Meanwhile, a “Western” diet was “characterized by the consumption of roast meat, sausages, hamburgers, steak, chips, crisps and soft drinks.”

Of course, all this assumes that you actually want a larger hippocampus. Sometimes it feels like having a smaller brain might be a better way of fitting in.

[h/t Munchies]