A UNSW Sydney study in rats, published in Molecular Nutrition and Food Research, shows that cycling between a healthy and unhealthy diet impacts a person's spatial memory.
The research was undertaken by Dr Mike Kendig and Prof Margaret Morris, Head of Pharmacology at UNSW Medicine & Health.
This research recognises that junk foods are a central part of modern diets, but most of us don't eat them 100% of the time.
People often take part in 'diet cycling', alternating between healthy and unhealthy eating.
A common pattern is adopting a poorer quality diet on weekends.
Previous research shows that high-fat, high-sugar diets are associated with poorer cognition in humans and rats.
However, the effects of diet cycling are not well understood.
"Mike and I wanted to know whether the same total amount of unhealthy food, but in different-sized chunks, would have the same impact," said Morris.
So why did the unhealthy diet impact the rats' memory? It's likely that several factors are at play - one being the gut microbiome.
"Our analyses indicated that the levels of two bacteria correlated with the extent of the memory impairment.
"This suggests a link between the effects of diet cycling on cognition and the microbiota," explained Kendig.
Morris added, "we know the gut is very connected to our brain.
"Changes to the microbiome in response to our diet might impact our brain and behaviour."
Another reason could be that an unhealthy diet contributes to inflammation in the body.
Morris stated that the key takeaway is that even subtle shifts in dietary habits can impact our thinking and memory.
Regular, long stretches of healthy eating are important for cognition.
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