Bad news if you love a nice weekend cheat meal: scientists have found evidence that "diet cycling" between healthy food Monday to Friday, followed by a weekend reward of greasy takeout, could trigger cognitive impairment and poor gut health.
The researchers out of the University of New South Wales, Australia, found that rats that ate healthy diets most of the time, but occasionally binged on elevated saturated-fat/high-sugar foods performed much worse on spatial memory tests in which they had to remember where objects were placed.
This impairment increased the longer that the rats were fed the unhealthy diet, with the animals that had eaten the fat- and sugar- rich foods for consecutive days found to perform the worst in memory tests.
This builds on earlier research, in which the team linked poor diet to long-term spatial memory, but this is the researchers' first look at exploring the impact of what’s perceived as moderation with healthy/unhealthy diet cycling.
“Our lab has been looking at the nexus between high-fat diet, high-sugar diet and cognition using a rat model,” said Margaret Morris, professor and Head of Pharmacology at UNSW Medicine & Health. “[We] wanted to know whether the same total amount of unhealthy food, but in different-sized chunks, would have the same impact.”
Over the course of 16 days, different periods of unhealthy food, as well as a healthy control, showed that time spent "cycling" between diets appeared to have a direct effect on both spatial memory and gut health.
The rats exposed to any period of unhealthy foods had a less diverse microbiome, including higher levels of the bacteria associated with obesity and fewer of the good kind associated with weight control. The change was more pronounced the longer the period of poor meals lasted.
What’s more, it offered the latest link between cognitive function and gut health.
"Our analyses indicated that the levels of two bacteria correlated with the extent of the memory impairment,” said co-author Mike Kendig, diet and cognition researcher at the University of Technology Sydney (UTS). “This suggests a link between the effects of diet cycling on cognition and the microbiota.”
There’s an increasing body of evidence directly linking gut health to memory and cognitive health, including research into bumblebee microbiota, and how fecal gut transplants have improved memory and brain function in several mice studies. Other molecular studies have also backed up this correlation.
And research has shown that a high-fat, high-sugar diet may reduce the size and function of the brain’s hippocampus region, essential for learning and memory.
“We know the gut is very connected to our brain,” said Morris. “Changes to the microbiome in response to our diet might impact our brain and behavior.”
Not surprisingly, the rats that spent the most time eating the high-fat, high-sugar diet gained more weight than the control animals. However the length of time spent eating poorly did not appear to impact weight.
While this may be good news for those who prefer a weekend of treats rather than just Friday night pizza, it also highlights how the effect on gut and memory health could be independent to weight gain associated with poor diet.
The researchers also link the unhealthy eating to increased inflammation, which impacts cognitive function.
“In humans we know that a diet that increases inflammation appears to be less beneficial for our brain function,” said Morris. “And in the past, we’ve shown in rats that these cognitive deficits actually correlate with inflammation in the brain.”
While the findings may put a dampener on cheese and wine nights, the scientists say the main takeaway is that the longer the stretch of healthy eating, the better it looks to be for guts and minds.
“We think this sort of work is critical to get us to think about maintaining the health of our brain into old age,” Morris added. “If we can maintain a healthy diet – such as the Mediterranean-type diet with high diversity, fruits, vegetables, low saturated fats, good proteins – we have a better chance of preserving our cognition.”
The research was published in the journal Molecular Nutrition & Food Research.
Source: University of New South Wales
