Research cautions diets high in fat and sugar can impair brain function

University of Sydney, Australia, researchers reveal that high-fat and high-sugar diets negatively affect people’s spatial navigation — learning and remembering a path from one location to another. The team says their findings confirm the importance of “making healthy dietary choices for cognitive health.”

The authors say this relationship between diet and brain function remained after controlling for body mass index (BMI) and performance on a non-spatial task. 

Spatial navigation can approximate the health of the brain’s hippocampus. The team explains that the effects of diets high in refined sugar and saturated fat on cognitive function likely center on the hippocampus, which is involved in spatial navigation and memory formation.  

“The good news is we think this is an easily reversible situation,” says Dr. Dominic Tran from the university’s School of Psychology. “Dietary changes can improve the health of the hippocampus, and therefore our ability to navigate our environment, such as when exploring a new city or learning a new route home.”

In the study in the International Journal of Obesity, 55 university students (aged 18–38) used a virtual reality maze to test the impact of diet. To complete the maze, participants needed to estimate distance and direction information to track their position and remember landmark locations. 

Virtual reality maze

Participants needed to navigate the maze six times to locate a treasure chest. They could use landmarks to remember their route, and the starting point and chest location of each trial remained constant. 

If the students found the treasure in under four minutes, they moved to the subsequent trial. However, if they failed this deadline, they were transported to the chest location and given ten seconds to familiarize themselves with it before the following trial. 

Sugar and fat intake were a reliable predictor of performance in a virtual reality maze, where students needed to find a treasure chest.In a seventh trial, the researchers removed the treasure chest from the maze and asked participants to mark its former location purely based on memory. 

Participants with diets lower in fat and sugar could pinpoint the location more accurately than students who consumed these foods several times per week. 

“After controlling for working memory and BMI, measured separately from the experiment, participants’ sugar and fat intake were a reliable predictor of performance in that final, seventh, test,” says Tran.  

Sugar and fat intake

The researchers note that their findings are consistent with those from animal studies but are the first to reveal the adverse effect of diet on spatial learning and memory in a task that requires navigation in three-dimensional space. 

“We’ve long known eating too much refined sugar and saturated fat brings the risk of obesity, metabolic and cardiovascular disease, and certain cancers,” says Tran. “We also know these unhealthy eating habits hasten the onset of age-related cognitive decline in middle-aged and older adults.” 

“This research gives us evidence that diet is important for brain health in early adulthood, a period when cognitive function is usually intact.” 

Last year, US researchers cautioned that high-fat and sugary diets in teens may permanently harm memory, based on a mouse-model study. Meanwhile, scientists flagged that women following a healthy diet with limited added sugar may lower their biological age. 

At the same time, Tran says the sample research group was not representative of the wider population, although the findings apply more broadly. 

“It’s likely our participants were a little healthier than the general population, and we think if our sample better represented the public, the impact of diet on spatial navigation would likely be even more pronounced.”