Can junk food harm our brains?

If you want to keep your brain in shape, stay away from fast food restaurants, bakeries and the grocery store candy aisle, according to an Oregon State University study.

Compared to an average diet, both a high-fat and a high-sugar diet caused changes to gut bacteria, which researchers linked to a decline in cognitive flexibility – or the ability to adapt and adjust to change. For the study, mice were fed diets that contained varying levels of sugar and fat and then attempted a variety of mazes and puzzles.

After four weeks, the rats fed a high-fat diet or a high-sugar diet had a decline in their mental and physical performance, especially when a part of the test was altered.

Researchers found that the mice on higher-fat or higher-sugar diets also had more unhealthy bacteria inside their gut, triggering a cognitive decline.

“It’s increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain,” says Kathy Magnusson, principal investigator and Oregon State University professor. “Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions.”

Dr. Aaron Miller, a neurologist at Advocate Sherman Hospital in Elgin, Ill., wants to see if the results of the study could also be replicated on humans. However, he notes that there are many studies linking diet with cognitive functioning, including one connecting a Mediterranean diet with a reduction in dementia and another which found that the brain was less adaptive in those consuming two ham, egg, and cheese biscuits for breakfast compared to subjects who did not eat anything.

“It’s logical to conclude that making poor food choices over the course of a lifetime would eventually cause longer-lasting adverse effects on cognition,” says Dr. Miller. “Diabetes and hypertension, both of which can relate to diet, are also risk factors for strokes, which lead to vascular dementia.”

In addition to a poor diet leading to cardiovascular disease or diabetes, researchers warned about the effect on the brain.

“This work suggests that fat and sugar are altering your healthy bacterial systems, and that’s one of the reasons those foods aren’t good for you.” Magnusson said. “It’s not just the food that could be influencing your brain, but an interaction between the food and microbial changes.”