Collage of brain scans and cheeseburger

Discrimination may disrupt how the brain and the gut talk to each other, raising risk of obesity, study finds

Experiencing discrimination may change how the brain and the gut communicate with each other, a new study has found. The disruption, the researchers say, could promote behaviors that increase people’s risk of obesity.

The study, published Monday in the journal Nature Mental Health, included more than 100 participants, mostly women, who filled out questionnaires to gauge their experiences of discrimination in their day-to-day lives. The participants then underwent brain scans as they were being shown pictures of sugary and fatty foods, such as cake and ice cream, along with pictures of lower-sugar and low-fat foods like fruit and salad. They also provided fecal samples so the researchers could study their gut microbiome.

In individuals who reported experiencing high levels of discrimination, the photos of unhealthy, high-calorie foods triggered a larger response in the reward processing region of the brain, called the frontal-striatal region. This part of the brain is also involved with motivation and executive control. 

That heightened response can lead people to reach for sugar and high-fat foods, the researchers said.

Sugar is highly addictive and is often craved by people undergoing stress, including from discrimination, as a means to provide comfort, said Arpana Gupta, an associate professor-in-residence of medicine at the UCLA David Geffen School of Medicine and senior author of the study.

“When you’re feeling sad and you’re feeling upset, what do you see on TV — that girl going to grab that tub of ice cream,” Gupta said. “It’s interesting that when we’re stressed, we crave these foods. We go for these foods for comfort. What our study was able to do was that it was able to show this at the brain level, as well as the gut level.”

At the gut level, she said, the study found that people who reported higher levels of discrimination had higher levels of the compounds known as glutamate metabolites. These compounds are associated with inflammation and oxidative stress, which can damage cells and DNA. 

Glutamate metabolites from the gut also play a major role in the function of the brain, Gupta said. Too much can affect regions of the brain related to cognition, leading to difficulty controlling cravings and responses to high-calorie foods among people who experience discrimination, Gupta said. 

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An excess of glutamate in the body can also lead to a deposition of body fat, especially in the abdominal region, said Dr. Cuckoo Choudhary, professor of medicine and division lead for women, diversity, equity and inclusion at Sidney Kimmel Medical College in Philadelphia. It can also increase a person’s craving for sugar and fatty foods, according to Choudhary, who was not involved with the new study.

Aside from putting a person at the risk of obesity, the study found that glutamate may also be involved in the biological mechanisms behind depression and anxiety-related disorders. 

However, Gupta said that more research is needed to more accurately measure glutamate in the brain. 

A “special relationship”

There is a “special relationship” between the brain and the gut that goes beyond just a connection, said  Dr. Pankaj Pasricha, a gastroenterologist and researcher at the Mayo Clinic in Phoenix. The brain receives information and provides feedback to the gut, for example, by sending signals to stop eating when a person’s stomach is full. 

While external stressors like discrimination can impact the gut, Pasricha said not everyone who experiences stress develops an overt health issue — and that both genetics and environment play a role.

“People don’t think about the gut as being exposed to the exterior, but in reality, it is,” Pasricha, who was not involved with the new research, said. “It just happens to be in our belly. It’s got an opening on both ends and it’s constantly being exposed to environmental factors. So, the gut becomes important.”

Increased stress, he added, can break down the gut barrier, which can trigger inflammation and even autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. 

Choudhary said that chronic stress can even exacerbate already existent gastrointestinal issues, including irritable bowel syndrome. And even at a low, constant level, discrimination “can cause chronic stress,” she added.

When it comes to people’s cravings for sugar, they could stem from childhood experiences, conditioned reflexes and memory, Pasricha said.

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“It’s a combination of our genetics, a combination of our social and cultural experiences — the bad stuff, like discrimination — and some of the good stuff,” Pasricha said. “We remember what our mother used to cook for us, and we find joy in going back.”

Does race play a role?

The new study didn’t look at the links between discrimination and race or ethnicity. 

However, Gupta’s previous research has found differences in how the brain and gut respond to discrimination depending on the race and ethnicity of the individual. In a 2022 study, Gupta and her colleagues reported that among Black and Hispanic individuals, discrimination was linked to changes in the brain associated with psychological coping and increased inflammation, while in white people, discrimination was linked to anxiety, but not inflammation. Among Asian individuals, the study found a link between discrimination and behavioral changes.

In an ideal world, Gupta said, the best way to address the risks presented in the study is to fight discrimination through policy changes. 

“I don’t think that discrimination is going to go away,” Gupta said. “I don’t think it’s going to go away in my lifetime. I don’t think it’s going to go away in my kid’s lifetime. So, what we need to do in the interim is do other things that can help us cope better with discrimination.” 

She advised that people take a multipronged approach by managing stress and being aware of their eating habits. Eating anti-inflammatory foods and probiotics can also help manage gut health.

Pasricha said innovations in medicine, including drugs like Ozempic, may also be a solution to help control eating habits. While it is “extremely difficult” to change human behavior, he said it is important to address social determinants of health, which can lead to inequalities in health care, delivery and access.

“As a society, we must recognize that these problems begin very early on,” he said, “and we must reduce the stressors that, if not mitigated or are prevented, will leave a permanent effect on the circuitry of the developing and vulnerable brain.”

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Claretta Bellamy

Claretta Bellamy is a fellow for NBC News.