UNSW research in rats shows that cycling between a healthy and unhealthy diet has significant health effects.
We all know this scenario. You’ve been sticking to a healthy diet, then the weekend rolls around. Pub meals, greasy fry-ups, takeaway dinners… None of that matters as long as you ate healthily during the week, right?
A UNSW Sydney study in rats, published in Molecular Nutrition and Food Research, shows that cycling between a healthy and unhealthy diet impacts spatial memory. The research was undertaken by Dr Mike Kendig and Professor Margaret Morris, Head of Pharmacology at UNSW Medicine & Health.
This research is important as junk foods are a central part of modern diets, but most of us don’t eat them 100 per cent of the time. People often take part in ‘diet cycling’, alternating between periods of 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 Prof Morris.
Unhealthy diet impaired memory
“Our lab has been looking at the nexus between high-fat diet, high-sugar diet and cognition using a rat model,” Prof Morris said.
In this study, adult male rats were exposed to a healthy diet of standard rat food. Some rats were also exposed to 16 days of an unhealthy ‘cafeteria’ diet, consisting of standard food plus high-fat, high-sugar, processed foods. This 16 days of unhealthy diet was done in one stretch, or broken up into shorter or longer ‘cycles’.
During the experiments, rats were exposed to healthy and unhealthy diets for varying durations.
Rats exposed to the unhealthy diet variations performed more poorly on spatial memory tests, where they had to remember the placement of objects. The memory impairment was more noticeable for rats who followed the high-fat, high-sugar diet for more consecutive days – in other words, longer unhealthy diet cycles.
The unhealthy diet also led to changes in the gut microbiome. 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,” said Dr Kendig.
Concerningly, eating unhealthy foods may also directly affect the structure of the brain. Previous research shows that a high-fat, high-sugar diet may reduce the size and function of a brain area called the hippocampus, which is essential for learning and memory.
