Young adults with a high body mass index (BMI) may have poorer episodic memory (the ability to recall past events) than their healthy weight peers, according to a new study at the University of Cambridge.
While only a small study, the findings add to the growing body of evidence that excess body weight may be associated with changes to the structure and function of the brain and its ability to perform certain cognitive tasks optimally.
Nearly 69 percent of U.S. adults and about 60 percent of U.K. adults are overweight or obese. Obesity increases the risk of physical health problems, such as diabetes and heart disease, as well as mental health disorders, such as depression and anxiety.
“Understanding what drives our consumption and how we instinctively regulate our eating behavior is becoming more and more important given the rise of obesity in society,” said Dr. Lucy Cheke.
“We know that to some extent hunger and satiety are driven by the balance of hormones in our bodies and brains, but psychological factors also play an important role — we tend to eat more when distracted by television or working, and perhaps to ‘comfort eat’ when we are sad, for example.”
In previous studies, obesity has been linked with dysfunction of the hippocampus, an area of the brain involved in memory and learning, and of the frontal lobe, the part of the brain involved in decision making, problem solving, and emotions.
Based on these associations, researchers wanted to know whether obesity could have a direct effect on memory.
“Increasingly, we’re beginning to see that memory — especially episodic memory, the kind where you mentally relive a past event — is also important. How vividly we remember a recent meal, for example today’s lunch, can make a difference to how hungry we feel and how much we are likely to reach out for that tasty chocolate bar later on,” said Cheke.
The researchers evaluated 50 participants aged 18-35, with BMIs ranging from 18 through to 51. A BMI of 18-25 is considered healthy, 25-30 is overweight, and over 30 is obese.
The participants completed a memory test known as the “Treasure-Hunt Task,” where they were asked to hide items around complex scenes (for example, a desert with palm trees) for two days. They were then asked to remember which items they had hidden, where they had hidden them, and when they were hidden.
The findings revealed a link between higher BMI and poorer performance on the tasks.
The researchers say the findings may suggest that the structural and functional changes in the brain previously found in those with higher BMI may be accompanied by a lowered ability to form and/or retrieve episodic memories.
Since the effect was demonstrated in young adults, it adds to growing body of evidence that the cognitive impairments linked to obesity may be present early in adult life.
Since this was a small, preliminary study, the researchers caution that further research is needed to fully determine whether the findings can be generalized to overweight individuals in general, and to episodic memory in everyday life rather than in experimental conditions.
“We’re not saying that overweight people are necessarily more forgetful,” Cheke said, “but if these results are generalizable to memory in everyday life, then it could be that overweight people are less able to vividly relive details of past events such as their past meals. Research on the role of memory in eating suggests that this might impair their ability to use memory to help regulate consumption.”
“In other words, it is possible that becoming overweight may make it harder to keep track of what and how much you have eaten, potentially making you more likely to overeat.”
Cheke said this work is an important step in understanding the role of psychological factors in obesity.
“The possibility that there may be episodic memory deficits in overweight individuals is of concern, especially given the growing evidence that episodic memory may have a considerable influence on feeding behaviour and appetite regulation,” she said.
The findings are published in The Quarterly Journal of Experimental Psychology.