Summary: Obesity isn’t just bad for physical health. Being overweight can have a significant impact on neurological health too. Researchers identified a link between obesity and reduced brain plasticity. Brain plasticity impairment could lead to cognitive and learning deficits in those suffering from obesity.
Source: University of South Australia
A world-first study has found that severely overweight people are less likely to be able to re-wire their brains and find new neural pathways, a discovery that has significant implications for people recovering from a stroke or brain injury.
In a new paper published in Brain Sciences, researchers from UniSA and Deakin University show that brain plasticity is impaired in obese people, making it less likely that they can learn new tasks or remember things.
Using a series of experiments involving transcranial magnetic stimulation, the researchers tested 15 obese people aged between 18 and 60, comparing them with 15 people in a healthy-weight control group.
Repeated pulses of electrical stimulation were applied to the brain to see how strongly it responded. The healthy-weight control group recorded significant neural activity in response to the stimulation, suggesting a normal brain plasticity response. In contrast, the response in the obese group was minimal, suggesting its capacity to change was impaired.
UniSA researcher Dr Brenton Hordacre says the findings provide the first physiological evidence of a link between obesity and reduced brain plasticity.
Obesity is based on body mass index (BMI) which calculates the ratio between height and weight to determine body fat. An adult who has a BMI between 25 and 29.9 is considered overweight. Anything above that is obese.
“Obesity is already associated with a raft of adverse health effects, including a higher risk of cardiovascular disease, metabolic disorders and dementia,” Dr Hordacre says.
“For the first time, we found that obesity was associated with impaired brain function, adding further support for the need to address the obesity epidemic.
“A growing number of people are obese – 650 million according to the World Health Organization – which not only has health consequences but is a serious financial burden for global health systems,” he says.
“These new findings suggest that losing weight is particularly important for healthy brain ageing or for recovery in people who suffer strokes or brain injuries, where learning is fundamental for recovery.”
Stroke is the third most common cause of death in Australia and the leading cause of disability, affecting speech, cognition and memory.
The ability of the brain to find new pathways is crucial to recovery, Dr Hordacre says. Worldwide, 15 million people suffer strokes each year, a third of whom die.
Obesity is Associated with Reduced Plasticity of the Human Motor Cortex
Obesity is characterised by excessive body fat and is associated with several detrimental health conditions, including cardiovascular disease and diabetes. There is some evidence that people who are obese have structural and functional brain alterations and cognitive deficits. It may be that these neurophysiological and behavioural consequences are underpinned by altered plasticity. This study investigated the relationship between obesity and plasticity of the motor cortex in people who were considered obese (n = 14, nine males, aged 35.4 ± 14.3 years) or healthy weight (n = 16, seven males, aged 26.3 ± 8.5 years). A brain stimulation protocol known as continuous theta burst transcranial magnetic stimulation was applied to the motor cortex to induce a brief suppression of cortical excitability. The suppression of cortical excitability was quantified using single-pulse transcranial magnetic stimulation to record and measure the amplitude of the motor evoked potential in a peripheral hand muscle. Therefore, the magnitude of suppression of the motor evoked potential by continuous theta burst stimulation was used as a measure of the capacity for plasticity of the motor cortex. Our results demonstrate that the healthy-weight group had a significant suppression of cortical excitability following continuous theta burst stimulation (cTBS), but there was no change in excitability for the obese group. Comparing the response to cTBS between groups demonstrated that there was an impaired plasticity response for the obese group when compared to the healthy-weight group. This might suggest that the capacity for plasticity is reduced in people who are obese. Given the importance of plasticity for human behaviour, our results add further emphasis to the potentially detrimental health effects of obesity.