The enduring allure of sugar can be traced back to our foraging ancestors, who sought out high-energy foods to sustain themselves. Today, this same craving often leads us to late-night trips to the store for a quick chocolate fix, despite our awareness of the numerous physical and metabolic issues linked to excess sugar, including obesity, diabetes, tooth decay, and even memory impairment.
The pressing question is, can a change in diet reverse the damage caused by high sugar consumption?
A recent systematic review and meta-analysis suggests that while it may be possible to mitigate some of the cognitive effects of sugary diets in rodent models, the recovery is likely only partial.
Some cognitive impairments might linger, even after one adopts healthier dietary habits.
The study revealed that reducing sugar intake can enhance memory in rodents previously exposed to high-sugar diets. However, their memory did not reach the same levels as that of rodents consistently fed healthier diets.
Previous research has connected high-fat, high-sugar (HFHS) diets with a range of neurocognitive and behavioral issues, although the persistence of these effects following dietary improvements remains uncertain.
In their study, researchers examined findings from 27 preclinical experiments involving rats and mice to better understand the impact of transitioning from HFHS diets to healthier options on cognitive function.
Lead author Simone Rehn, a biopsychologist at the University of Technology Sydney (UTS) in Australia, states, “Our results show that improving diet quality does benefit memory.” However, “those improvements were incomplete. Even after weeks on a healthy diet, memory did not return to the level seen in animals that had never eaten an unhealthy diet.”
Rehn and her team employed systematic reviews and meta-analyses to uncover broader trends from their study pool. They concentrated on diet and memory, while also keeping track of other cognitive indicators, including general activity, food motivation, and behaviors linked to anxiety or depression.
Rodents that were switched to healthier food after at least two weeks on unhealthy diets consistently performed better on memory tests compared to those still consuming junk food.
However, no consistent improvements were observed in other cognitive measures following dietary changes, indicating that these effects were specific to memory.
The memory enhancements varied by diet type, showing more significant gains when high-fat diets were replaced with healthier options, while little recovery was seen in responses to high-sugar or HFHS diets.
Rehn adds, “We saw clearer memory improvements after high-fat diets were replaced with healthy food. But diets high in added sugar, including those high in both fat and sugar, showed little evidence of recovery. This suggests sugar may be a key factor in limiting memory recovery.”
According to senior author Mike Kendig, also a biopsychologist at UTS, rodent models were essential for isolating the impact of diet on memory. He notes, “In humans, changes in diet usually coincide with shifts in exercise, mood, and daily routines, making it difficult to separate the effects of diet alone on brain function.”
The findings are particularly relevant to the hippocampus, a brain area crucial for memory and learning, which also plays a role in appetite regulation.
Prior studies have linked HFHS diets in humans to reduced hippocampal volume and functioning, a correlation bolstered by this research.
The authors of the study suggest, “Our findings imply that diet reversal primarily improves hippocampal-dependent spatial memory, highlighting evidence that the hippocampus is particularly responsive to dietary changes and other environmental factors.”
While the stakes are high concerning sugar intake, the message is not one of despair regarding past consumption but rather a call to recognize the importance of reducing sugar intake sooner rather than later.
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Kendig notes, “There is a common belief that the effects of unhealthy eating are easily reversible. These results suggest that, at least for memory, the picture may be more complex, especially with diets high in added sugar.” He emphasizes the significance of improving diet quality while also highlighting the importance of avoiding prolonged exposure to unhealthy diets, as the effects may not always be fully recoverable later.
This research was published in Nutritional Neuroscience.
