A fine line between pleasure and weight gain

The size of your brain’s pleasure and reward processing sensors could be behind increased body fat in adolescents and potentially obesity later in life, new research by Monash University has found.

Published in Nature Scientific Reports on Thursday 28 February 2019, the study results showed there was a strong link between body fat and size of the nucleus accumbens (NAcc) – also known as the ‘pleasure centre’ of the brain – in adolescents.

An individual’s body fat percentage was also found to correlate with the size of their medial orbitofrontal cortex (OFC) – a region at the front of the brain that is involved in reward processing of food cues.

As our brains become accustomed to the high rewards from impulsivity – the tendency to act on a whim without consideration of the consequences – body fat acquired from adolescence could develop into obesity with age due to a lack of behavioural change.

Led by Dr Naomi Kakoschke from the Monash Institute of Cognitive and Clinical Neurosciences (MICCN), this is one of the first studies in the world to examine the link between excess body fat and brain health in adolescents and adults.

Co-authors of the study included Professor Antonio Verdejo-Garcia, also from MICCN, and Dr Valentina Lorenzetti (School of Psychology) and Associate Professor Karen Caeyenberghs (Mary MacKillop Institute for Health Research) from the Australian Catholic University.

“We know that both reward-based learning and executive control are compromised in people who are overweight or obese. People with excess weight show heightened responsivity to highly palatable food cues, such as television commercials for food, and less ability to control those unhealthy urges,” Dr Kakoschke said.

The study examined the association between body fat (an index of weight severity), impulsivity (a vulnerability factor for obesity) and brain structure in 127 people across the body mass index (BMI) spectrum. It also provides initial evidence of the link between BMI and NAcc volumes among adolescents using body fat as an indicator of obesity.

Findings showed that body fat was up to 3% higher in adolescents who had a larger left NAcc than similar people in their age bracket. The volume of an individual’s left medial OFC was also positively associated with an increase in body fat due to the role it plays in reward and emotion processing.

Previous research in children demonstrates that responsivity to food advertisements and higher NAcc volume are associated with genetic risk for obesity and higher body fat composition.

This also supports the early formation of unhealthy eating behaviours due to a combination of enhanced reward-related sensitivity in the striatum and impulsivity-related alterations in the structure of the prefrontal cortex.

“We know that excessive body fat accumulation increases the risk of developing chronic health conditions including cardiovascular disease, Type 2 diabetes and dementia, but we need to look at how the workings of our brain play a part in this body fat gain,” Dr Kakoschke said.

“Studies have repeatedly shown that reward sensitivity is elevated in people with obesity, particularly for those with binge eating disorder. We hope future studies can point to brain health as being a more accurate indicator of body composition and body fat than BMI.”