It’s not just willpower: How obesity may change communication in the adolescent brain

The conversation surrounding adolescent obesity has long been dominated by a familiar refrain: “Eat less, move more.”

We tend to treat weight as a simple equation of diet, lifestyle and willpower. However, a recent study challenges this conventional wisdom by looking directly at the mechanics of the adolescent brain. The reality of obesity is more complex than what’s on a teenager’s plate and may be linked to differences in how brain regions communicate.

The study found that adolescents with obesity show altered communication between brain regions involved in appetite regulation, reward and decision-making.

“I think it highlights that obesity is a neurologic disease,” said the author of the study, Marc-Andre Cornier, M.D., professor of medicine and director of the Division of Endocrinology, Diabetes and Metabolic Diseases at MUSC, about the study findings.

Autopilot versus decision maker

The brain is controlled by two different systems that constantly communicate with one another. When it comes to hunger and eating, actions are driven by a delicate conversation between the homeostatic and nonhomeostatic brains.

“ The higher brain, which is what tells us to actually do things, interacts with our homeostatic brain, and it’s those interactions that are really important to help people to make the right decisions about eating,” said Cornier.

The homeostatic system functions like the body’s unconscious autopilot, automatically regulating hunger and fullness. This autopilot keeps a person’s weight stable.

The nonhomeostatic system is the conscious decision maker. It’s responsible for cognitive function and reward processing. The decision maker moves beyond basic survival and processes external factors like the smell of freshly baked cookies. It ultimately dictates the choices we make about what, when and how much to eat.

When the body needs fuel, the autopilot needs to send a clear signal to the decision maker, which then helps him or her choose a nutritious meal. When full, the autopilot needs to signal the decision maker to resist the extra cookie, no matter how tempting it looks.

When things are running smoothly, the two systems are in constant communication. But when those lines of communication are altered, the balance shifts.

What the study found

The researchers compared 30 adolescents with severe obesity to 26 healthy-weight adolescents. Participants underwent brain scans while fasting and after drinking a 300-calorie glucose beverage to simulate a fed state.

“Adolescents with obesity have altered communication between homeostatic parts of the brain, the parts that control appetite and body weight regulation, and nonhomeostatic parts of the brain involved in reward and cognitive function.”

When fasting, adolescents with obesity showed weaker connectivity between the hypothalamus and regions involved in sensory processing and coordination and stronger connectivity with regions involved in processing bodily sensations.

After drinking the glucose beverage, adolescents with obesity showed altered hypothalamic communication with several brain regions involved in reward and motivation, executive function and decision-making.

The researchers found that communication between homeostatic and nonhomeostatic brain regions differed from that of healthy-weight adolescents. The signals passing between involuntary appetite regulation and higher-level decision-making appeared to be altered.

“It’s those interactions that are really important to help people make the right decisions about eating, and this communication appears to be disrupted based on the study findings.”

Obesity may be changing the brain – or vice versa

This raises a “chicken-or-egg” question – whether these brain differences contribute to obesity in the first place or whether they develop as a consequence of it.

“The question is,” Cornier noted, “’Is this the cause of these people’s obesity, or is this a result of their obesity? Or is it both?’ We can’t tell that.”

One possibility is that the relationship works in both directions. Altered brain communication could contribute to obesity while obesity itself may further disrupt appetite regulation over time.

“ There's growing evidence that when you overeat, especially higher-fat foods, it can cause inflammation in the hypothalamus, and that potentially disrupts body weight regulation further. So it kind of causes a snowballing effect.”

Moving past willpower

Perhaps the biggest takeaway from this study, Cornier explained, is its potential to help to dismantle the stigma surrounding adolescent obesity. By providing evidence that obesity is associated with altered brain communication, this research challenges the notion that adolescent obesity is simply the result of laziness, poor parenting or a lack of discipline. When it’s recognized as a neurological condition rather than a result of lifestyle choices, approaches to treatment can evolve.

“This really highlights the underlying neurologic nature of this disease, and that it needs to be treated as such,” said Cornier.

The findings may also help to pave the way for more effective and empathetic ways to support adolescents living with obesity.

“Many people still believe that obesity is a choice, a weakness, a lack of willpower,” he said. “But these adolescents aren’t choosing to have obesity. They’re not choosing to have this difference in their brain activity.”