It's a familiar situation for many of us: maintaining a healthy diet throughout the week, only to indulge in pub meals and takeaway dinners over the weekend. But does our weekend indulgence have any impact if we are healthy during the weekdays? A study by UNSW Sydney, published in Molecular Nutrition and Food Research, offers some insights.
The research, conducted by Dr. Mike Kendig and Professor Margaret Morris, reveals that alternating between healthy and unhealthy diets - a pattern known as 'diet cycling' - can affect spatial memory. This subject is particularly important in our time when junk foods play a substantial role in everyday diets, even though they're not consumed continuously. A common trend involves shifting to a lesser-quality diet over the weekend.
Earlier studies suggest that high-fat, high-sugar diets can impair cognition in both humans and rats. However, the impact of diet cycling on cognition is still a gray area. Kendig and Morris aimed to explore whether varying amounts of unhealthy food would lead to similar effects.
The study exposed adult male rats to a regular healthy diet. Some rats also experienced 16 days of an unhealthy 'cafeteria' diet, which included standard food with high-fat, high-sugar processed foods. The 16-day junk food diet was either given continuously or divided into shorter or longer cycles.
The results showed that the rats on the unhealthy diet had poorer performance on spatial memory tests. This was especially true for the rats that consumed the high-fat, high-sugar diet for a longer continuous period. Moreover, the unhealthy diet caused significant alterations in the gut microbiome, decreasing the diversity of microbial species, increasing the levels of 'bad' bacteria linked with obesity, and reducing the 'good' bacteria associated with weight control.
Interestingly, all rats on the unhealthy diet gained more weight than the control group fed a healthy diet. However, the duration of the unhealthy diet didn't seem to influence the cognitive effects or changes in the gut microbiome.
The correlation between diet and cognition is likely due to multiple factors, including changes in the gut microbiome and bodily inflammation caused by an unhealthy diet. Unhealthy eating may also directly influence the brain's structure. Prior research indicates that a high-fat, high-sugar diet could diminish the size and function of the hippocampus, a crucial area for learning and memory.
While more research is required to comprehend why diet cycling influenced the rats' memory and its applicability to humans, the study emphasizes the potential cognitive impact of even minor shifts in our dietary habits. Regular, extended periods of healthy eating might be crucial for maintaining cognitive function.
Adhering to a healthy diet like the Mediterranean diet, rich in diversity, fruits, vegetables, low saturated fats, and high-quality proteins, may enhance our chances of preserving our cognitive health as we age.
Michael D. Kendig et al, Obesogenic Diet Cycling Produces Graded Effects on Cognition and Microbiota Composition in Rats, Molecular Nutrition & Food Research (2023). DOI: 10.1002/mnfr.202200809