Obesity ‘linked to poorer memory’ — but the evidence is pretty thin

The latest figures from the Health Survey for England suggest that 61.7 per cent of adults are overweight or obese. Our expanding waistlines have inspired a deluge of headlines about the effects this has on our health, but less attention has been paid to the psychological effects of overeating.

Research published in the Quarterly Journal of Experimental Psychology suggests that a higher body mass index (BMI) is linked with reduced ‘episodic memory’ — or the ability to store, maintain, and recall complex information about and the context of events.

The researchers had 50 participants (aged between 18 and 35 with BMIs ranging from 18 to 51) carry out a ‘treasure-hunt task’ which required them to recollect an object, its location, and when they saw it.

They found that increased BMI was associated with significantly lower performance on the test and its individual elements: object identification, location memory, and temporal order memory. They say that having controlled for age, sex, and years in education, the reduced performance associated with higher BMI remained.

The researchers also suggest there is evidence for episodic memory’s role in appetite regulation — and that this could help to explain why obese people can struggle to control their eating habits.

However, their study has by no means proved a link between obesity and poor episodic memory (see our expert verdict below).

The research is the latest to suggest that excess bodyweight is associated with changes in the brain’s structure and function; in November we reported that in obese children, the smell of food may be activating a different part of the brain.

Expert verdict
Episodic memory is a person’s unique memory of a specific event such as the recent consumption of food.

In this study the authors tested a novel episodic memory test — the ‘treasure hunt task’ — to see if people who are obese have a worse episodic memory; the idea being that this might explain their overeating. The headline claim from the reasearch was that obesity is associated with episodic memory defects.

However the results could also be explained by chance, bias or confounding.

The study sample was small — restricted to 50 individuals — so that when other factors such as age, gender and years of education are taken into account the overall results do not achieve statistical significance. This suggests that the main finding could simply have arisen by chance.

The other problem with this paper that might explain the results is bias — a particular concern is that some participants were recruited by ‘word of mouth’ rather than by any random process.

Confounding is where a third factor — that is associated with both the obesity and, independently, with the memory problem — might account for the results. One obvious candidate to explain the findings that the researchers did not take into account is sleep disruption.

Research score: 1/5