Australian researchers have discovered that a short-term diet of foods high in fat and sugar can have a detrimental effect on the brain’s cognitive ability.

Researchers from the University of New South Wales (UNSW) have demonstrated that rats fed a diet high in fat and sugar had an impaired memory after just a week. Interestingly, researchers said rats fed a healthy diet but given access to sugar water to drink had similarly poor results.

The research, which has been published in the journal Brain, Behaviour and Immunity, tested cognitive impairment related to place recognition. The animals showed poorer ability to notice when an object had been shifted to a new location. These animals also had inflammation of the hippocampal region of the brain, which is associated with spatial memory.

“We know that obesity causes inflammation in the body, but we didn’t realise until recently that it also causes changes in the brain,” said Professor Margaret Morris from UNSW Medicine, and one of the authors of the study.

The change in the animals’ memory appeared even prior to the emergence of weight differences between the animals.

“What is so surprising about this research is the speed with which the deterioration of the cognition occurred,” said Professor Morris. “Our preliminary data also suggests that the damage is not reversed when the rats are switched back to a healthy diet, which is very concerning,” she said.

Not all memory affected

Some aspects of the animals’ memories were spared, regardless of their diets. All the animals were equally able to recognise objects after eating either the “healthy”, “cafeteria” (high in fat and sugar, including cake, chips and biscuits) or “healthy with sugar” regimes.

Researchers said ongoing work will attempt to establish how to stop the inflammation in the brain of animals with unhealthy diets.

“We suspect that these findings may be relevant to people,” Professor Morris said. “While nutrition affects the brain at every age, it is critical as we get older and maybe be important in preventing cognitive decline. An elderly person with poor diet may be more likely to have problems,” she said.

Researchers said this study builds on previous work that has implications for obesity.

“Given that high energy foods can impair the function of the hippocampus, if you eat a lot of them it may contribute to weight gain, by interfering with your episodic memory,” Professor Morris said. “People might be less aware of their internal cues like hunger pangs and knowing when they have had enough,” she said.

The research, conducted by Professor Morris and colleagues Jessica Beilharz and Jayanthi Maniam, was funded by the National Health and Medical Research Council.

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