Date Published: 23 July 2012

Overeating and increased weight linked to the nucleus accumbens in the brain

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People who are overweight have a high BMI

Recent research suggests that the consumption of snacks (i.e. food eaten between meals) and weight gain and high body mass index (BMI), which are associated with overeating, are linked to both brain activity and self-control.

The researchers found that an individual's brain 'reward centre' response to pictures of food predicted how much they subsequently ate. This appeared to have more effect on the amount they ate than their conscious feelings of hunger or how much they wanted the food.

A strong brain response was also associated with increased weight (BMI), but only in individuals reporting low levels of self-control on a questionnaire. For those reporting high levels of self-control a stronger brain response to food was actually related to a lower BMI.

This recent study (see ref. below) contributes to mounting evidence that overeating and increased weight are linked in part to a region of the brain associated with motivation and reward, called the nucleus accumbens. Responses in this part of the brain have been shown to predict weight gain in healthy weight and obese individuals, but academics only recently discovered that this is independent of conscious feelings of hunger, and that self-control also plays a key role.

As a consequence of the recent study scientists have started testing 'brain training' techniques designed to reduce the influence of food cues on individuals who report low levels of self-control. Similar tests are being used to assist those with gambling or alcohol addiction.

Dr Natalia Lawrence of Exeter University, lead researcher in both the original research and the latest study, said:

" Our research suggests why some individuals are more likely to overeat and put on weight than others when confronted with frequent images of snacks and treats. Food images, such as those used in advertising, cause direct increases in activity in brain 'reward areas' in some individuals but not in others. If those sensitive individuals also struggle with self-control, which may be partly innate, they are more likely to be overweight. We are now developing computer programs that we hope will counteract the effects of this high sensitivity to food cues by training the brain to respond less positively to these cues."

Twenty-five young, healthy females with BMIs ranging from 17-30 were involved in the study. Female participants were chosen because research shows females typically exhibit stronger responses to food-related cues. The hormonal changes during the menstrual cycle affect this reaction, so all participants were taking the monophasic combined oral contraceptive pill. Participants had not eaten for at least six hours to ensure they were hungry at the time of the scan and were given a bowl containing 150 g (four and a half packets) of crisps to eat at the end of the study; they were informed that crisp intake had been measured afterwards.

Researchers used MRI scanning to detect the participants' brain activity while they were shown images of household objects, and food that varied in desirability and calorific content. After scanning, participants rated the food images for desirability and rated their levels of hunger and food craving. Results showed that participants' brain responses to food (relative to objects) in the nucleus accumbens predicted how many crisps they ate after the scan. However, participants' own ratings of hunger and how much they liked and wanted the foods, including crisps, were unrelated to their crisp intake.

Ref. to Paper:
"Nucleus accumbens response to food cues predicts subsequent snack consumption in women and increased body mass index in those with reduced self-control" by Natalia Sophie Lawrence, Eleanor C Hinton, John A Parkinson, Andrew D Lawrence, pub in NeuroImage (http://www.journals.elsevier.com/neuroimage/). Researchers were based at the Universities of Bangor, Bristol, Cardiff and Exeter.

Source: Bristol University, England (UK)
http://www.bristol.ac.uk

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