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Diets High In Fat, Sugar May Decrease Cognitive Functioning

Last updated June 24, 2015

Approved by: Maulik P. Purohit MD, MPH

When you eat something loaded with sugar, your taste buds, your gut and your brain all take notice. This activation of your reward system is not unlike how bodies process addictive substances such as alcohol or nicotine -- an overload of sugar spikes dopamine levels and leaves you craving more. Nicole Avena explains why sweets and treats should be enjoyed in moderation.

According to a new study at the Oregon State University, diets high in fat or sugar may reduce cognitive functioning. Published in the journal Neuroscience, the researchers found that these diets may cause changes in a person’s microbiome. An individual's microbiome is comprised of trillions of bacteria that live inside the body including the gut, which has an effect on a person’s “cognitive flexibility” or the ability to think and adapt in the world.

Principle investigator Professor Kathy Magnusson suggests there is growing evidence signifying that gut bacteria can communicate with the brain.

"It's increasingly clear that our gut bacteria, or microbiota, can communicate with the human brain," said Magnusson in a press release. "Bacteria can release compounds that act as neurotransmitters, stimulate sensory nerves or the immune system, and affect a wide range of biological functions," she said. "We're not sure just what messages are being sent, but we are tracking down the pathways and the effects."

In the animal study, Magnusson and colleagues randomly separated two-month old male mice based on their diets. Mice were used because they provide a useful model for studies relevant to human beings. The diet options were the following: a high-fat diet (42% fat, 43% carbohydrate), a high-sugar diet (12% fat, 70% carbohydrate - mainly simple sugars), or regular chow. Before and two weeks after, the researchers analyzed the mice’s feces to understand their gut bacteria composition. They also measured their short- and long-term memory with their cognitive ability by using a water maze before and after the diet changes.

Results showed that after just four weeks on either a high-fat or a high-sugar diet, the performance of mice on various tests of mental and physical function began to decrease, compared to animals on a chow diet. One of the more prominent changes was found in the mice’s cognitive flexibility.

The researchers suggest the study’s results may show the dangers of the “Western diet”, which is typically high in sugar, fat, and simple carbohydrates and linked to the growing obesity epidemic and incidences in Alzheimer’s disease.

“We’ve known for a while that too much fat and sugar are not good for you,” Magnusson said. “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. It’s not just the food that could be influencing your brain, but an interaction between the food and microbial changes.”

Primary References:

Magnusson, K. R., Hauck, L., Jeffrey, B. M., Elias, V., Humphrey, A., Nath, R., ... & Bermudez, L. E. (2015). Relationships between diet-related changes in the gut microbiome and cognitive flexibility. Neuroscience, 300, 128-140.

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 24, 2015
Last updated: June 24, 2015