On the Site:


Obesity changes the brain, with ‘no sign of reversibility,’ expert says

Jun 12, 2023, 10:45 AM

Being obese interrupts gut-to-brain signals about nutrients, and that disruption remains, even afte...

Being obese interrupts gut-to-brain signals about nutrients, and that disruption remains, even after weight loss, a new study found. Mandatory Credit: RealPeopleGroup/E+/Getty Images

(CNN) — Obesity may damage the brain’s ability to recognize the sensation of fullness and be satisfied after eating fats and sugars, a new study found.

Further, those brain changes may last even after people considered medically obese lose a significant amount of weight — possibly explaining why many people often regain the pounds they lose.

“There was no sign of reversibility — the brains of people with obesity continued to lack the chemical responses that tell the body, ‘OK, you ate enough,’” said Dr. Caroline Apovian, a professor of medicine at Harvard Medical School and codirector of the Center for Weight Management and Wellness at Brigham and Women’s Hospital in Boston.

As defined medically, people with obesity have a body mass index, or BMI, of over 30, while normal weight is a BMI of between 18 and 25.

“This study captures why obesity is a disease — there are actual changes to the brain,” said Apovian, who was not involved in the study.

“The study is very rigorous and quite comprehensive,” said Dr. I. Sadaf Farooqi, a professor of metabolism and medicine at the University of Cambridge in the UK, who was not involved in the new research.

“The way they’ve designed their study gives more confidence in the findings, adding to prior research that also found obesity causes some changes in the brain,” she said.

Nutrients delivered by feeding tube

The study, published Monday in Nature Metabolism, was a controlled clinical trial in which 30 people considered to be medically obese and 30 people of normal weight were fed sugar carbohydrates (glucose), fats (lipids) or water (as a control). Each group of nutrients were fed directly into the stomach via a feeding tube on separate days.

“We wanted to bypass the mouth and focus on the gut-brain connection, to see how nutrients affect the brain independently from seeing, smelling or tasting food,” said lead study author Dr. Mireille Serlie, professor of endocrinology at Yale School of Medicine in New Haven, Connecticut.

The night before the testing, all 60 study participants had the same meal for dinner at home and did not eat again until the feeding tube was in place the next morning. As either sugars or fats entered the stomach via the tube, researchers used functional magnetic resonance imaging (fMRI) and single-photon emission computed tomography (SPECT) to capture the brain’s response over 30 minutes.

“The MRI shows where neurons in the brain are using oxygen in reaction to the nutrient — that part of the brain lights up,” Faroof said. “The other scan measures dopamine, a hormone that is part of the reward system, which is a signal for finding something pleasurable, rewarding and motivating and then wanting that thing.”

Researchers were interested in how fats and glucose would individually trigger various areas of the brain connected to the rewarding aspects of food. They wanted to know if that would be different in people with obesity compared to those of normal weight.

“We were especially interested in the striatum, the part of the brain involved in the motivation to actually go and look for food and eat it,” Serlie said. Buried deep in the brain, the striatum also plays a role in emotion and habit formation.

In people with normal weight, the study found brain signals in the striatum slowed when either sugars or fats were put into the digestive system — evidence that the brain recognized the body had been fed.

“This overall reduction in brain activity makes sense because once food is in your stomach, you don’t need to go and get more food,” Serlie explained.

At the same time, levels of dopamine rose in those at normal weight, signaling that the reward centers of the brain were also activated.

Different findings for medically obese

However, when the same nutrients were given via feeding tube to people considered medically obese, brain activity did not slow, and dopamine levels did not rise.

This was especially true when the food was lipids or fats. That finding was interesting, Farooqi said, because the higher the fat content, the more rewarding the food: “That’s why you will genuinely want a burger instead of broccoli, the fat in the burger will biologically give a better response in the brain.”

Next, the study asked people with obesity to lose 10% of their body weight within three months — an amount of weight known to improve blood sugars, reset metabolism and boost overall health, Serlie said.

Tests were repeated as before — with surprising results. Losing weight did not reset the brain in people with obesity, Serlie said.

“Nothing changed — the brain still did not recognize fullness or feel satisfied,” she said. “Now, you might say three months is not long enough, or they didn’t lose enough weight.

“But this finding might also explain why people lose weight successfully and then regain all the weight a few years later — the impact on the brain may not be as reversible as we would like it to be.”

2018 meta-analysis of long-term weight loss clinical trials found 50% of a person’s original weight loss was regained after two years — by the fifth year, 80% of the weight was regained.

More research needed

Caution is needed in interpreting the findings, Serlie said, as much is unknown: “We don’t know when these profound changes in the brain happen during the course of weight gain. When does the brain start to slip and lose the sensing capacity?”

Obesity has a genetic component, and although the study attempted to control for that by excluding people with childhood onset obesity, it’s still possible that “genes are influencing our response in the brain to certain nutrients,” said Farooqi, who has studied the role of genes on weight for years.

Much more research is needed to fully understand what obesity does to the brain, and if that is triggered by the fat tissue itself, the types of food eaten, or other environmental and genetic factors.

“Are there changes that occurred in people as they gained weight? Or are there things that they were eating as they were gaining weight, such as ultra-processed foods, that caused a change in the brain? All of these are possible, and we don’t really know which it is,” Farooqi said.

Until science answers these questions, the study emphasizes, once again, that weight stigma has no place in the fight against obesity, Serlie said.

“The belief that weight gain can be solved simply by ‘just eating less, exercising more, and if you don’t do that, it’s a lack of willpower is so simplistic and so untrue,” she said.

“I think it’s important for people who are struggling with obesity to know that a malfunctioning brain may be the reason they wrestle with food intake,” Serlie said. “And hopefully this information will increase empathy for that struggle.”

The-CNN-Wire™ & © 2023 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.

KSL 5 TV Live


IN SPACE - In this handout provided by the National Aeronautics and Space Administration, Earth as ...

Ashley Strickland, CNN

Astronomers discover nearby six-planet solar system with ‘pristine configuration’

Astronomers have used two different exoplanet-detecting satellites to solve a cosmic mystery and reveal a rare family of six planets located about 100 light-years from Earth. The discovery could help scientists unlock the secrets of planet formation.

10 hours ago

A wolverine walks on snow in Montana.
Mandatory Credit:	Mike Hill/Getty Images...

 Rachel Ramirez, CNN

Wolverines receive protection under Endangered Species Act as climate change threatens their habitat

The North American wolverine has officially been listed as threatened under the Endangered Species Act.

16 hours ago

FILE - Infowars founder Alex Jones appears in court to testify during the Sandy Hook defamation dam...

Nicki Brown, CNN

Sandy Hook families offer to settle for at least $85 million with Alex Jones

The families of Sandy Hook shooting victims offered Infowars host Alex Jones a “path out of bankruptcy” if he pays them a “small fraction” of the more than $1 billion he owes in damages, according to a court document.

1 day ago

Palestinians walk through damaged buildings in Gaza City. (Mohammed Hajjar, Associated Press)...

Mostafa Salem and David Shortell, CNN

Deal reached to extend Israel-Hamas truce by two days, Qatar says

A truce in the conflict between Israel and Hamas has been extended by two days, key mediator Qatar has said, in order to secure the release of 20 additional hostages held by the militant group.

2 days ago

Alex Murdaugh stands next to the witness booth during a break in his trial for murder at the Collet...

Dianne Gallagher, CNN

Alex Murdaugh is set to be sentenced today for nearly 2 dozen financial crimes

Alex Murdaugh – the disgraced former South Carolina attorney serving two life sentences for the murders of his wife and son – is set to be sentenced on Tuesday for nearly two dozen state financial crimes.

2 days ago

Pictured are Meta corporate headquarters in Menlo Park, California, in 2022.
Mandatory Credit:	Josh...

 Brian Fung, CNN

FTC can seek tough new restrictions on Meta’s use of personal data, federal judge rules

The judge's decision allows the FTC to move ahead with a proposal banning Meta from profiting off data it collects from users under the age of 18.

2 days ago

Sponsored Articles

Stylish room interior with beautiful Christmas tree and decorative fireplace...

Lighting Design

Create a Festive Home with Our Easy-to-Follow Holiday Prep Guide

Get ready for festive celebrations! Discover expert tips to prepare your home for the holidays, creating a warm and welcoming atmosphere for unforgettable moments.

Battery low message on mobile device screen. Internet and technology concept...

PC Laptops

9 Tips to Get More Power Out of Your Laptop Battery

Get more power out of your laptop battery and help it last longer by implementing some of these tips from our guide.

Users display warnings about the use of artificial intelligence (AI), access to malicious software ...

Les Olson

How to Stay Safe from Cybersecurity Threats

Read our tips for reading for how to respond to rising cybersecurity threats in 2023 and beyond to keep yourself and your company safe.

Design mockup half in white and half in color of luxury house interior with open plan living room a...

Lighting Design

Lighting Design 101: Learn the Basics

These lighting design basics will help you when designing your home, so you can meet both practical and aesthetic needs.

an antler with large horns int he wilderness...

Three Bear Lodge

Yellowstone in the Fall: A Wildlife Spectacle Worth Witnessing

While most people travel to this park in the summer, late fall in Yellowstone provides a wealth of highlights to make a memorable experience.

a diverse group of students raising their hands in a classroom...

Little Orchard Preschool

6 Benefits of Preschool for Kids

Some of the benefits of preschool for kids include developing independence, curiosity, and learning more about the world.

Obesity changes the brain, with ‘no sign of reversibility,’ expert says