New research suggests that there is a "reciprocal relationship" between obesity and the brain's prefrontal cortex — an area scientists associate with self-control, among other functions.
But more and more neuroscientific studies show that physiological reactions we are not even aware of, let alone have a say over, regulate much of our appetite.
For instance, studies have suggested that upon entering a restaurant, our brains are unconsciously responding to the surrounding food cues, causing us to eat more than we planned.
Moreover, a recent study has shown that a hormone called asprosin controls "hunger" neurons in our brains. The hormone "switches on" appetite-stimulating neurons while "silencing" the activity of appetite-suppressing neurons.
New research has now looked deeper into the connection between appetite, self-control, and the brain. Specifically, Cassandra Lowe, a BrainsCAN postdoctoral fellow at the Western University in Ontario, Canada, led scientists who examined the link between obesity and a brain area they typically associate with self-control — the prefrontal cortex.
Lowe and colleagues wondered if there were individual variations in the structure and functionality of the prefrontal cortex that might "predispose" someone to consuming too many "calorie-dense foods." Conversely, they questioned if obesity leads to changes in the structure and functionality of this brain area.
The researchers published their findings in the journal Trends in Cognitive Sciences.
The role of the prefrontal cortex in obesity
As Lowe and colleagues explain in their work, in order to account for obesity, existing neuroscientific studies have so far centered on the reward-processing mechanisms and areas in the brain. Namely, the "striatum, midbrain, amygdala, and orbitofrontal cortex," as well as the dopamine-releasing dorsal striatum have been the focus of much research.
However, explain the authors of the latest review, the prefrontal cortex may be just as crucial. This area is important for executive function, complex decision making, and planning future actions; the area also acts as a "filter" that helps a person express the appropriate response to a social situation.
Lowe and colleagues say there is a significant body of research suggesting that individuals who have less prefrontal cortex activity when making a decision may also be prone to craving more calorie-dense foods. Such people may also be more vulnerable to food cues, such as food advertisements.
But the story does not end here. Such behaviors say the researchers, in turn, may inform changes in the brain that then lead to food overconsumption in a mutually reinforcing relationship between obesity and the prefrontal cortex.
"It's not just the case that obesity is causing these issues in the brain structure and function, but it is this reciprocal relationship — that differences in brain structure and function can cause obesity — that's really important," says Lowe.
"Our review shows that if you have lower prefrontal activity, it can predispose you to overeating, which in turn can lead to weight gain and obesity."
The authors hope that the findings will pave the way for new treatments. "By reframing the issue of obesity around prefrontal activity, as opposed to reward region responsivity, we can explore treatments and preventative measures that may inhibit unwanted weight gain," Lowe explains.
How exercise and mindfulness could help
Some of the things we can do to improve the activity of our prefrontal cortex and implicitly regulate our eating behaviors include exercise and mindfulness.
"Exercise has been shown to increase activity in our prefrontal cortex," suggests Lowe, "which in turn lets us better ignore food cravings, going well beyond its traditional role as merely a means of getting rid of surplus calories."
Also, "By focusing on the healthiness and long-term consequences of the food we are eating instead of just taste, we are able to make better dietary choices," continues Lowe, referring to the benefits of mindfulness.
Study co-author Amy Reichelt, who is also a BrainsCAN postdoctoral fellow at Western University, explains the role of the prefrontal cortex in the eating habits of teens.
"Making good eating habits during our formative childhood and adolescent years can help set healthy eating up for life and ensure the prefrontal cortex functions correctly," Reichelt says.
"At this age, an adolescent's prefrontal cortex is not fully developed, which in part explains the impulsive and hot-headed decision making of our youth — the control system isn't fully engaged yet."
"Related to this aptitude for poor decision making are poor eating habits," continues the researcher, "with adolescents eating more unnecessary calories from junk foods than any other age group, a habit that can last into adulthood."
However, the authors admit that more research is needed to certify the benefits of exercise and mindfulness for treating obesity, as well as to determine how best to implement these therapies.