High body mass index (BMI) has been associated with certain health risks, which may now include cognitive impairment, according to preliminary research published in The Quarterly Journal of Experimental Psychology. The study, led by researchers from the University of Cambridge, found that young adults who are overweight may have poor episodic memory — a weakened ability to recall past events compared to their normal-weight peers.  

"We're not saying that overweight people are necessarily more forgetful," cautions lead study author Dr. Lucy Cheke in a statement, "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." About 69 percent of U.S. adults age 20 years and over are overweight or obese, according to the Centers for Disease Control and Prevention. Obesity increases the risk of heart disease, stroke, type 2 diabetes and certain types of cancers. It is also a major risk factor for premature mortality.

For the study, researchers' recruited 50 participants aged 10 to 35, with BMIs ranging from 18 to 31 — a normal BMI falls between 18.5 and 24.9. The participants completed a memory test known as the "Treasure-Hunt Task," where they were asked to hide items around complex scenes, such as a desert with palm trees, across two days. They were then asked to remember which items they had hidden, where they had hidden them, and when they were hidden. Overall, the team found an association between higher BMI and poorer performance on the tasks.

"Although only a small study, its results support existing findings that excess bodyweight may be associated with changes to the structure and function of the brain and its ability to perform certain cognitive tasks optimally," researchers wrote.

The recent study builds on and contributes to previous research that have linked memory problems to excess body weight. A 2013 study found that obesity and obesity-related health conditions may trigger changes in areas within the brain, particularly the hippocampal structure and function, which can hinder its ability to perform certain cognitive tasks optimally. The hippocampus is an area of the brain involved in memory and learning. And another study published earlier this year found that snacking on junk food late at night can negatively influence learning and memory.

"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," Cheke said.

Cheke also believes episodic memory plays an important part in an individual's eating habits, because "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."

Without an ability to keep track of what you eat, it may then cause you to overeat.

"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 [behavior] and appetite regulation," Cheke added.

Beyond its small size, limitations of the study may include the use of BMI to measure healthy weight, as recent studies have suggested that it is no longer a good indication of whether or not someone is healthy — with millions of Americans being mislabeled as overweight or obese.

Source: Cheke L, Simons J, Clayton N. Higher Body Mass Index is associated with Episodic Memory Deficits in Young Adults. The Quarterly Journal of Experimental Psychology. 2016.