Our fondness for sugar once helped our hunter-gatherer ancestors make the most of scarce, high-calorie foods. Today, it’s driving us back to the store for our insatiable chocolate cravings.
We do this even though we’re aware of sugar’s many physical and metabolic risks, such as obesity, diabetes, tooth decay, and even reduced memory function.
But how effectively can we reverse the damage by changing our diets?
According to a new systematic review and meta-analysis, the cognitive consequences of consuming a lot of sugar in rodents can be reversed, but perhaps only partially. The research findings were published in the journal Nutritional Neuroscience.
Some impairments persist even after switching to a healthier diet.
The study found that reducing sugar intake can improve memory in rodents previously fed a high-sugar diet, but it doesn’t restore memory to the levels seen in their counterparts who consistently ate healthy food.
Previous studies have linked high-fat, high-sugar (HFHS) diets to a range of neurocognitive and behavioral effects, but it remains unclear how resilient these effects are if the diet improves.
In the new study, researchers analyzed the findings of 27 preclinical studies, including controlled experiments in rats and mice, hoping to find out how switching from a HFHS diet to a healthier one affects cognitive function.
“Our findings indicate that improving diet quality does indeed benefit memory,” says study co-author Simone Renn, a biopsychologist at the University of Technology Sydney (UTS) in Australia. “But these improvements were not complete. Even after several weeks of healthy eating, memory did not return to the levels seen in animals that had never eaten unhealthy food.”
By conducting a systematic review and meta-analysis, Renn and her colleagues sought to identify common patterns found across more than two dozen studies.
They focused on the impact of diet on memory, but also tracked other potential indicators of cognitive effects, such as general activity, food motivation, and anxiety-depressive states.
The study showed that among rodents fed unhealthy food for at least two weeks, those switched to healthier food for at least 24 hours consistently performed better on memory tests than those who continued to eat the unhealthy food.
Other cognitive measures did not show consistent improvements related to dietary changes, suggesting the effects were specific to memory.
The effects impacting memory varied by diet type: significant improvements were seen in models using high-fat diets, but not in high-sugar diets or high-fat, high-sugar diets.
“We saw a more pronounced improvement in memory after replacing a high-fat diet with healthy food,” says Renn. “However, diets high in added sugar, including diets high in both fat and sugar, showed little to no signs of recovery. This suggests that sugar may be a key factor limiting memory recovery.”
As study co-author Mike Kendig, a biopsychologist at the University of Technology Sydney, explains, rodent models have been crucial in isolating the effects of diet on memory.
“In humans, changes in diet usually happen in conjunction with changes in physical activity, mood, and routine, making it very difficult to isolate the impact of diet alone on brain function,” says Kendig.
All of this appears to center around the hippocampus, a brain region vital for memory and learning, and also involved in appetite regulation.
High-fat, high-sugar diets in humans have previously been shown to be linked to reduced hippocampal volume and impaired function, and this is borne out by the new study.
“Our findings suggest that dietary change primarily improves hippocampal-dependent spatial memory, supporting a specific sensitivity of the hippocampus to changes in diet and other environmental factors,” the researchers write.
Despite memory impairment, the takeaway isn’t to despair over all the sugar consumed, but rather to recognize the seriousness of the situation and cut back on sugar intake as soon as possible.
“It’s a common belief that the consequences of unhealthy eating are easily reversible. These results show that, at least for memory, it might be more complicated, especially when added sugar is involved,” says Kendig. “Improving diet quality is still worthwhile. But protecting brain health might also depend on avoiding prolonged exposure to unhealthy foods, rather than assuming the consequences can always be fully undone later.”
About the Author
