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Researchers are learning how obesity can impact your brain so you don’t feel as full as often. ideasRojas/Getty Images
  • A new study finds that obesity can impact your brain, which can affect key hormones.
  • A link between the brain and obesity has been largely studied, but its long-term implications are still being evaluated.
  • A study found brain changes related to obesity may result in whether or not people feel full after eating.

​Obesity and its impact on the brain have been studied for years, but new research shows how weight gain may impact the brain itself.

In a new study in Nature Metabolism, researchers have discovered the alterations associated with obesity in the brain may have long-term impacts – even after someone loses weight – preventing long-lasting weight loss.

The researchers found that brain changes may result in people no longer getting signals that they’re full.

Traditionally when somebody eats a meal, signals are sent to the brain to notify it that the body is full or has a satisfactory content of food. However, scientists have discovered that the impact of obesity on the brain could be irreversible even after weight loss, resulting in regaining weight.

A link between the brain and obesity has been largely studied, but its long-term implications are still being evaluated.

“It’s not necessarily that people haven’t eaten enough, it’s that they aren’t receiving those signals to the parts of the brain that are responsible for the good feelings that comes from food,” said Lizzy Davis PhD RDN, Assistant Professor and Dietitian Education Program Director in the Department of Nutrition Sciences at the University of Alabama at Birmingham.

Experts explain that hormone levels help regulate appetite and energy.

“It is understood that key hormonal signals, such as leptin and insulin, which regulate appetite and energy homeostasis, are often dysregulated in obesity,” said Dr. Sahar Takkouche, lead expert in Bariatric and Obesity Medicine and assistant professor in the division of Diabetes, Endocrinology, and Metabolism at the Vanderbilt University Medical Center in Tennessee.

In this study, researchers conducted a controlled trial with 60 individuals, 30 who are medically obese (a BMI of greater than 30) and 30 who are of non-obese weight (a BMI of 25 or less). During testing, participants were fed carbohydrates, fats, or water (control) by using a nasogastric tube, a direct pathway to the stomach that bypasses the mouth, to understand the direct connection between the gut and the brain.

The night before the testing, all participants had the same meal. When the participants received carbohydrates, fats, or water during testing, their brains were evaluated through functional MRI (fMRI) and single photon emission computer tomography (SPECT) to understand the brain’s response to these foods.

By using these testing techniques, researchers were able to understand food’s effect on the various reward centers of the brain – particularly in an area called the striatum.

When looking at this area, researchers discovered that in lean people, there was slowing in the striatum resulting in the brain understanding that the body was fed, and dopamine levels also increased indicating feeling satisfied.

However, in patients with medical obesity, there was no slowing in the striatum, dopamine levels did not rise, and resultingly, the brain did not recognize the sensation and satisfaction of being full after eating.

Takkouche explains that dopamine is a critical neurotransmitter responsible for “reward, motivation, and pleasure systems in the brain.”

“The reward deficiency hypothesis proposes that diminished responses in the brain’s reward system to food stimuli and obesity lead to increased food consumption to achieve the same level of pleasure,” she explained.

“We thought there would be different responses between lean people and people with obesity, but we didn’t expect this lack of changes in brain activity in people with obesity,” said Dr. Mireille Serlie, lead study author and professor of endocrinology at the Yale School of Medicine, in a press release.

The medically obese patients were then asked to lose approximately 10% of their body weight within 3 months – an amount that is already scientifically known to improve metabolism, body sugar, and improve overall health.

Interestingly, those participants who did lose the 10% did not have any change in their brain’s ability to recognize fullness or feeling satisfied.

Davis explains, “The lean group did see significantly higher release of dopamine, compared to the obese and the 10% weight loss group and this is important because dopamine is the reward transmitter and sends the signal of pleasure.”

“This means the lean group got more of a pleasure and satisfactory sense from the infusion of lipids, compared to the obese group, pre and post 10% weight loss,” Davis continued.

According to the World Health Organization, 4 million people die each year due to the effects of overweight or obesity.

As medical experts learn about the biological effects of obesity, they are having more luck and finding long lasting obesity treatments.

This research leads to the idea that those who lose weight may quickly regain their weight back as there may be an irreversible change within the brain in medically obese individuals.

Obesity is a complex idea that has many ramifications for the brain.

“Obesity engenders a state of chronic low-grade inflammation which is linked to alterations in brain function and may lead to cognitive impairment, mood disorders, and increased risk of neurodegenerative diseases – this complex relationship between obesity and brain signaling is a critical subject of ongoing research,” Takkouche told Healthline.

While this data and information are compelling, there’s more to be learned about the brain and obesity.

“We do need to be careful about our takeaway from this paper as the sample size was small and the study design does not allow for a cause-and-effect takeaway. In other words, we are not able to say that this causes obesity,” Davis told Healthline.

Serlie says the next step is to understand when the brain does this. “We need to find where that point is when the brain starts to lose its capacity to regulate food intake and what determines that switch. Because if you know when and how it happens, you might be able to prevent it.”

“Losing weight is not just about ‘eat less, move more’ – and there’s a lot going on in our bodies, especially in our brains, that we’re just beginning to understand,” says Takkouche.

“It’s important to be patient with ourselves and others who are trying to lose weight as it can be more complex than it seems,” she said.

Dr. Rajiv Bahl, MBA, MS, is an emergency medicine physician, board member of the Florida College of Emergency Physicians, and health writer. You can find him at RajivBahlMD.