Young adults with a high body-mass index perform worse on memory tests than those who are leaner
Most of us are well aware of the health risks associated with obesity. Being overweight or obese is associated with an increased risk of numerous other conditions, from high blood pressure, heart disease and stroke, to diabetes, gout and some forms of cancer.
Research published over the past few years shows that obesity also has neurological consequences – it is associated with altered function in, and shrinkage of, certain parts of the brain, particularly the frontal lobes, which are the seat of intelligence, and the hippocampus, which is critical for memory formation. A new study now shows that this in turn is associated with impaired memory function.
Lucy Cheke of the University of Cambridge and her colleagues recruited 50 volunteers aged between 18 and 35, with Body Mass Indexes (BMIs) ranging from 18 (underweight) to 51 (extremely obese), and asked them to perform a computerised memory test called the “Treasure Hunt Task”. This involved moving food items around around complex scenes, such as a desert with palm trees, hiding them in various locations, and indicating afterwards where they had hidden them.
The participants were then shown various locations from the computerised scenes, and some of the food items, and asked if they had hidden something in each of the locations, or where they had hidden each of the items. Finally, they were shown pairs of the food items they had seen, and asked to indicate which of each pair they had hidden first.
The researchers found that participants with higher BMI performed significantly worse on this “what-where-when” test, apparently because of an impaired ability to ‘bind’ the different elements of the task, such as spatial location and the identity of the objects, into coherent and vivid memories. This is in keeping with earlier studies, carried out with both animals and humans, which show that obesity has a significant impact on brain structure and function, and adds to the growing body of evidence suggesting that the mental deficits associated with obesity are present early in life.
The researchers point out that these are preliminary results which need to be replicated, however. One important limitation is that the Treasure Hunt Task was devised especially for the study, and so it is not a standardised or well-established way of testing memory function. Another is that the researchers did not take certain other health conditions, such as hypertension and sleep apnea, into account – both of which usually occur with obesity, and are also known to impact mental function.
Thought for food
Even so, the results offer intriguing insights into the relationship between memory and feeding behaviour. Earlier studies have shown that amnesic patients who cannot remember what they just ate sometimes eat consecutive meals, apparently without feeling full up, and that manipulating memories of recent meals can influence peoples’ subsequent perceptions of how filling they are. These findings have led some researchers to argue that there is a vicious cycle of obesity and decline in mental function, whereby excess body weight impacts learning, which in turn impairs peoples’ memories of recent meals, and also their ability to regulate food consumption.
While the new findings suggest that people with higher BMIs may have memory deficits compared to leaner individuals, more research is needed to confirm that they are indeed less able to encode memories, and to investigate exactly how memory and food consumption are related to one another. Such research could eventually lead to new ways of regulating food consumption and controlling the global obesity epidemic.
Cheke, L. G., et al. (2016). Higher body mass index is associated with episodic memory deficits in young adults. Q. J. Exp. Psychol. DOI:10.1080/17470218.2015.1099163 [Full text]
This article was written by Mo Costandi, for theguardian.com on Thursday 3rd March 2016 11.00 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010