Junk food reduces thinking power and memories – new report

Foods high in saturated fat and refined sugar reduce the human brain’s capacity to store memories, say Australian researchers.

It’s established that too much saturated fat and refined sugar causes obesity, heart disease and some cancers, but thinking ability also declines and brain disorders increase in people on high fat-high sugar diets, says Dr Dominic Tran of the University of Sydney who is lead author of a paper published in the International Journal of Obesity.

“We also know these unhealthy eating habits hasten the onset of age-related cognitive decline in middle age and older adults,” Tran told Cosmos.

It’s not just older people; children and teenagers suffer too. Such brain effects happen “well in advance of increases in body weight.”

Effects on memories are felt in the hippocampus, the seahorse shaped brain organ (hippos, meaning ‘horse’, ‘kampos’ meaning ‘sea monster’) housing memory. Paired hippocampi, one on each side, sit deep within the brain’s temporal lobes, above and forward of the ears.

“When you eat a lot of crap, including saturated free fatty acids, which basically is fat meat, rubbish stuff, you get neuroinflammation,” says Professor Frédéric Meunier, of the Brain Institute at the University of Queensland.

“Neuroinflammation has an impact on spatial memory and is the trigger here,” says Meunier, who was not involved in the research. “You’ve got three major pathways which are bad for memory acquisition. Neuroinflammation is number one.

“The second is neurotrophic (‘neuron-building’) factors which are very, very good for brain development and memory formation. These neurotropic factors are actually reduced by high fat diet.

“And then you have the development potentially of insulin resistance in the central nervous system”

There is also a major difference between free fatty acids which are eaten, and those made in the body. “Free fatty acids are actually generated in the brain and are absolutely necessary for acquiring memory,” says Meunier. 

Much of the work on memories has been done on rats and mice. Now the Australian researchers have put humans through the maze.

Fifty-five university students, male and female, aged between 18 and 38 were asked to navigate a virtual reality maze seven times, to find a treasure chest. The chest was in the same place 6 times, but removed on the 7^th, and the students had to pinpoint where it had been. They also were asked to complete a questionnaire capturing estimated sugary and fatty food intake over 12 months, and body mass index (BMI) was recorded.

So, it was about learning and remembering the route, says Tran.

Students who did not eat fatty, sugary foods could more accurately remember where the chest had been much better than their counterparts who were regularly eating junk food.  BMI and working memory were included in calculations. 

“The good news is we think this is an easily reversible situation,” says Tran.

“Dietary changes can improve the health of the hippocampus, and therefore our ability to navigate our environment, such as when we’re exploring a new city or learning a new route home.” 

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

Tran acknowledges that the sample group used in this research was not representative of the wider population, “but the findings still 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. 

“This paper is interesting because it basically confirms what we knew already about diet in rodents, and confirmed that this is also bad for humans,” says Meunier.

Creating memories