Those who successfully slim down tend to gain back 50% of that weight within 2 years, and 80% within 5 years. Meanwhile, the obesity epidemic marches on.

But a new frontier of brain-based therapies – from GLP-1 agonist drugs thought to act on reward and appetite centers to deep brain stimulation aimed at resetting neural circuits – has kindled hope among patients like Smith and the doctors who treat them. The treatments, and theories behind them, are not without controversy. They’re expensive, have side effects, and, critics contend, pull focus from diet and exercise. 

Butmost agree that in the battle against obesity, one crucial organ has been overlooked.

“Obesity, in almost all circumstances, is most likely a disorder of the brain,” said Casey Halpern, MD, an associate professor of neurosurgery at the University of Pennsylvania. “What these individuals need is not simply more willpower, but the therapeutic equivalent of an electrician that can make right these connections inside their brain.”

A recent study, not yet published, from Hall’s lab drew a slightly different conclusion, suggesting that people with obesity actually have too much dopamine, filling up those receptors so the pleasure spike from eating doesn’t feel like much.

“It’s kind of like trying to shout in a noisy room. You’re going to have to shout louder to have the same effect,” said Hall.

Gut-brain pathways that tell us we’re full may also be impaired.

In another study, Yale researchers tube-fed 500 calories of sugar or fat directly into the stomachs of 28 lean people and 30 people with obesity. Then they observed brain activity using functional magnetic resonance imaging (fMRI).

In lean people, about 30 regions of the brain quieted after the meal, including parts of the striatum (associated with cravings).

In those with obesity, the brain barely responded at all. 

“In my clinic, patients will often say ‘I just finished my dinner, but it doesn’t feel like it,’” said senior author Mireille Serlie, MD, PhD, an obesity researcher at the Yale School of Medicine. “It may be that this nutrient-sensing interaction between the gut and the brain is less pronounced or comes too late for them after the meal.”

In people with obesity, he said, the thermostat – or set point the body seeks to maintain – is too high.

All this raises a crucial question: How do these circuits and pathways malfunction in the first place?

What Breaks the Brain?

Genes, scientists agree, play a role. 

Studies show that genetics underlie as much as 75% of people’s differences in body mass index (BMI), with certain gene combinations raising obesity risk in particular environments. 

While hundreds of genes are believed to have a small effect, about a dozen single genes are thought to have a large effect. (Notably, most influence brain function.) For instance, about 6% of people with severe obesity since childhood have mutations in a gene called MC4R (melanocortin 4 receptor), which influences leptin signaling.

Still, genetics alone cannot account for the explosion in obesity in the U.S. over the last 50 years, says epidemiologist Deirdre Tobias, ScD, an assistant professor of medicine at Harvard Medical School.

“This is a stark example of how, when you can change the food environment, you cause really remarkable changes in food intake without people even being aware that they are overeating,” said Hall. 

Just what it is about these relatively novel foods that may trigger overeating is unclear. It could be the crunch, the lack of water content, the engineered balance of sugar/salt/fat, their easy-to-devour texture, or something else. 

Some research suggests that the foods may interfere with gut-brain signaling that tells the brain you’re full. 

“Evidence is amassing that the nutritional content of processed foods is not accurately conveyed to the brain,” wrote Dana Small, PhD, a neuroscientist at Yale, in a recent perspective paper in Science. 

Even more concerning: Some animal studies suggest processed foods reprogram the brain to dislike healthy foods.

And once these brain changes are made, they are hard to reverse.

“The problem is, our brain is not wired for this,” said Halpern. “We are not evolved to eat the food we are eating, so our brain adapts, but it adapts in a negative way that puts us at risk.”

The weight began to fall off again.

Smith’s success story is just one of many that Stanford, an obesity medicine doctor-scientist at Harvard, has heard in her office in recent years.

“I do not believe these drugs are a panacea,” she said. “There are non-responders, and those are the patients I take off the medication. But for the high-responders, and there are many of them, they are telling me, ‘Oh my gosh. For the first time in my life, I am not constantly thinking about eating. My life has changed.’” 

A Multi-Pronged Approach

Halpern, at Penn, has also been hearing success stories.

In recent years, he has placed permanent electrodes in the brains of three people with grade III, or severe, obesity and binge eating disorder. 

All had tried exercise, dieting, support groups, medication, and weight loss surgery to no avail.

Thus far, all three are seeing promising results.

“It’s not like I don’t think about food at all,” one of them, Robyn Baldwin, told The New York Times. “But I’m no longer a craving person.”

Halpern is now extending the trial to more patients and hopes to ultimately include other areas of the brain, including those that involve memory.

He imagines a day when people with severe obesity, who have failed conventional treatments, can walk into a clinic and have their brain circuits assessed to see which ones may be misfiring.

Many might find relief with noninvasive brain stimulation, like transcranial magnetic stimulation (already in use for depression). Others might need a more extreme approach, like the deep brain stimulation, or DBS, therapy Halpern used.

“Obviously, DBS is hard to scale, so it would have to be reserved for the most severe patients,” he said.

Still, not everyone believes brain-based drugs and surgeries are the answer. 

David Ludwig, MD, PhD, a professor of nutrition at the Harvard School of Public Health, played a key role in the discovery of GLP-1 and acknowledges that “of course” the brain influences body composition. But to him, explaining obesity as a disease of the brain oversimplifies it, discounting metabolic factors such as a tendency to store too much fat.

He noted that it’s hard to get drug companies, or any agencies, to fund large clinical trials on simple things like low-carbohydrate diets or exercise programs.

“We need all the tools we can get in the battle against the obesity epidemic, and new technologies are worth exploring,” he said. “However, the success of these drugs should not lead us to deprioritize diet and lifestyle interventions.” 

Stanford, who has received consulting fees from Wegovy, believes the future of treatment lies in a multi-pronged approach, with surgery, medication, and lifestyle changes coalescing in a lasting, but fragile, remission.