国产精品

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Maddie Massy-Westropp
国产精品 Medicine & Health
m.massywestropp@unsw.edu.au

We all know this scenario. You鈥檝e been sticking to a healthy diet, then the weekend rolls around. Pub meals, greasy fry-ups, takeaway dinners鈥 None of that matters as long as you ate healthily during the week, right?

A 国产精品 Sydney study in rats, published in , 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 国产精品 Medicine & Health.

This research is important as junk foods are a central part of modern diets, but most of us don鈥檛 eat them 100 per cent of the time. People often take part in 鈥榙iet cycling鈥, alternating between periods of healthy and unhealthy eating. A common pattern is adopting a poorer quality diet on weekends.

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.

鈥淢ike and I wanted to know whether the same total amount of unhealthy food, but in different sized chunks, would have the same impact,鈥 said Prof. Morris.

Unhealthy diet impaired memory

鈥淥ur lab has been looking at the nexus between high-fat diet, high-sugar diet and cognition using a rat model,鈥 said Prof. Morris.

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 鈥榗afeteria鈥 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 鈥榗ycles鈥 (see diagram below).

Diagram showing experimental design with alternating healthy and unhealthy diet

During the experiments, rats were exposed to healthy and unhealthy diets for varying durations. Note that this diagram is illustrative only and does not fully reflect the experimental design. Image: Ian Joson.

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 鈥 in other words, longer unhealthy diet cycles.

The unhealthy diet also led to changes in the gut microbiome. This included less diversity in the microbial species present, higher levels of 鈥榖ad鈥 bacteria associated with obesity, and lower levels of 鈥榞ood鈥 bacteria associated with weight control. These effects became more severe with longer unhealthy diet cycles.

All of the rats fed the unhealthy diet gained more weight than controls fed the healthy diet by the end of the experiment. However, the length of the 鈥榰nhealthy cycle鈥 had little impact. In other words, the effects on cognition and gut microbiome appeared to be independent of weight gain.

Links between diet and cognition

So why did the unhealthy diet impact the rats鈥 memory? It鈥檚 likely that several factors are at play 鈥 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,鈥 said Dr Kendig, who undertook this research at 国产精品 and now researches diet and cognition at the Faculty of Science at (UTS).

Prof. Morris added: 鈥淲e know the gut is very connected to our brain. Changes to the microbiome in response to our diet might impact our brain and behaviour.鈥

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Another reason could be that an unhealthy diet contributes to inflammation in the body.

鈥淚n humans we know that a diet that increases inflammation appears to be less beneficial for our brain function,鈥 said Prof. Morris. 鈥淎nd in the past, we鈥檝e shown in rats that these cognitive deficits actually correlate with inflammation in the brain.鈥

Concerningly, eating unhealthy foods may also directly affect the structure of the brain. 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. 聽

Diagram showing connection between unhealthy diet, gut microbiota and cognition. Burger, intestines and brain are shown.

Diet is thought to affect cognition directly through inflammation and structural changes to the brain, as well as indirectly due to changes in the gut microbiota. Image: Ian Joson.

Maintaining brain health

Further research is needed to understand exactly why the diet cycling impacted the rats鈥 memory, and how well this translates to humans.

However, Prof. Morris said 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 probably important for our cognition.

鈥淲e think this sort of work is critical to get us to think about maintaining the health of our brain into old age,鈥 Prof. Morris said.

鈥淚f we can maintain a healthy diet 鈥 such as the Mediterranean-type diet with high diversity, fruits, vegetables, low saturated fats, good proteins 鈥 we have a better chance of preserving our cognition.鈥