We all agree that eating well is important for our health. But isn’t it acceptable to treat yourself to an unhealthy meal or two on the weekend?
A study by researchers at the University of New South Wales (UNSW) in Australia suggested that a diet of “clean” eating interspersed with “cheat” meals or junk food could not only lead to weight gain, but also improve brain function and gut health. can affect. rodents.
Rats that ate mostly healthy, but occasionally indulged in foods high in sugar and saturated fat, showed significant cognitive impairment, especially on tests of spatial memory, and negative changes in gut bacteria.
“We think this kind of work is critical to getting us thinking about preserving our brain health into old age,” explains UNSW neuroscientist Margaret Morris.
The study is expanding preliminary investigation by members of the team who found a link between poor diet and impaired long-term spatial memory, providing new information about the effects of ‘diet cycles’.
Sometimes seen as a compromise between extremes of healthy and unhealthy eating, the fluctuations in diet can come at a cost.
In each of the 3 different experiments, a healthy control group of 12 rats was fed standard rat chow, compared to 3 experimental groups of 12 rats that were also fed processed foods high in fat and sugar at times.
The experimental groups spent a total of the same number of days eating unhealthy foods, consecutively or spread over ‘cycles’ of different lengths.
Before and after the diet cycles, the researchers tested the rats’ short-term memory and measured the microbiota in their feces. They also weighed them before and after and tracked how much of each food type the rats consumed.
Rats that ate poorly for extended periods of time had a less diverse gut microbiome, with more bacteria associated with obesity and fewer strains of good bacteria associated with weight management. With longer exposure to an unhealthy diet, these changes got worse.
Cognitive impairment also became more severe over time, with the rats fed an unhealthy diet for several days performing worst on memory tests that required recall of object placement.
“Our analyzes indicated that the levels of two bacteria correlated with the extent of memory impairment,” say Mike Kendig, then a medical scientist at UNSW. “This suggests a link between the effects of diet cycles on cognition and the microbiota.”
It is therefore not surprising that the rats that followed a high-fat and sugar-rich diet for a long time gained more weight than the rats in the control group. But the length of bad eating cycles didn’t seem to directly affect weight gain.
This indicates that the effects on gut and memory health may not be related to the weight gain usually caused by an unhealthy diet.
“In humans, we know that a diet that increases inflammation appears to be less beneficial for our brain function,” say Morris. “And in the past, we’ve shown in rats that these cognitive deficits actually correlate with inflammation in the brain.”
![A blue background with mages of a citizen, a brain and a stomach with intestine, connected in a circle with arrows.](https://www.sciencealert.com/images/2023/05/diet-cycling-impacts-s-1.jpg)
These results add to the growing body of evidence linking gut health and nutrition to brain health.
“We know that the gut is strongly connected to our brain,” Morris adds. “Changes in the microbiome in response to our diet can affect our brains and behavior.”
While these findings may not be what we want to hear, the scientists emphasize that sticking to a healthy diet for longer seems to have more beneficial outcomes for both gut and brain health.
Other studies suggest that good nutrition reduces disease risk and can add years to your life, so it may be worth swapping high-fat and sugary treats for healthier options.
“If we can maintain a healthy diet – such as the Mediterranean diet with high diversity, fruits, vegetables, low in saturated fats, good protein – we have a better chance of preserving our cognition,” Morris concludes.
The study is published in Molecular nutrition and nutrition research.