Oct. 20, 2023 – People who eat more ultra-processed foods – particularly artificial sweeteners and-artificially sweetened drinks – could be at higher risk of depression, according to new research.

The study was published recently in JAMA Network Open.

Ultra-processed foods are energy-dense and ready-to-eat food items including things like processed breakfast meats, packaged snacks, and ice cream as well as artificially sweetened drinks. Artificial sweeteners, also an ultra-processed food, include things like aspartame, sucralose, and saccharine.

“What we found is that consuming high amounts of ultra-processed foods could increase your risk of developing depression by up to 50%,” said Raaj Mehta, MD, MPH, one of the study’s authors and a gastroenterologist at Massachusetts General Hospital in Boston.

This study adds to growing concerns about these kinds of foods, he said.

It’s just another piece of evidence that these foods harm our bodies, he said, and not just our physical health.

“The reason why this is so important is that people aren’t always aware of the connection between nutrition and diet and mental health, and so I think what this could do is really encourage physicians to start to have those conversations that what you’re eating does actually affect potentially how you’re feeling,” Mehta said.

He said that because this is an observational study – one that looked at data already gathered – they cannot say highly processed food causes depression. That said, he thinks the data is strong.

“We were able to adjust for a number of what are called confounding variables in our analysis to suggest that eating more ultra-processed foods really could increase your risk of depression.”

“Sometimes what you see when you adjust for these variables is that the models or the results get weaker. And we didn’t really see that at all,” he later said. 

Mehta said he wanted to do the study to examine the “gut-brain axis,” which he described as a “bidirectional highway between your intestines and the brain.”

“We looked at the literature and saw that there was some data that diet affected risk of depression, but we didn’t, at the end of the day, know which specific foods are responsible.” 

Ultra-processed foods have been linked to health conditions ranging from diseases of the heart and blood vessels to dementia to cancer, Mehta said, but there really wasn’t much evidence about the risk of depression.

Researchers did the analysis using the Nurses’ Health Study II between 2003 and 2017 among 31,712 middle-aged women without depression at the start of the study. They looked at the patients’ diet every 4 years using food surveys.

In a later analysis, they grouped ultra-processed food into subgroups such as ultra-processed grain foods, ready- to-eat meals, processed dairy products, sweet snacks, drinks and artificial sweeteners, etc.

They took into account other possible risk factors for depression, including smoking, exercise level, body mass index (BMI), alcohol use, total energy intake, other diseases that people in the study had, and more. Authors evaluated the link between changes in ultra-processed consumption updated every 4 years and rates of depression.

Researchers found that the women who ate a lot of ultra-processed food also had a higher BMI; higher smoking rates; higher rates of diabetes and hypertension; and were less likely to exercise regularly.

Over the 15-year period, 2,122 cases of depression were found using a strict definition of depression and 4,840 using a broader definition.

Authors then examined the link between specific categories of ultra-processed food and the risk of depression. The results showed that only artificially sweetened beverages and artificial sweeteners were linked with a higher risk of depression.

“After finding that these ultra-processed foods were linked with depression, our question was: What within the large group of foods could explain our results?” Mehta said. 

He and his team tested different kinds of food for risk of future depression. “And that’s when we found that artificially sweetened beverages and other sweeteners were linked with depression, but not the other groups,” he said. 

How that link between artificial sweeteners and artificially sweetened drinks could occur is unknown, the authors write, but recent experimental data suggests that artificial sweeteners create specific transmissions in the brain, which may be part of the explanation, the authors write. 

“There’s been some really interesting data in mice that show that when you give artificial sweeteners and regular sugar … they have totally different neurotransmission signals in the brain,” Mehta said.

“When you look at the overall category of ultra-processed foods, the strength of the effect does seem to be larger than the artificial sweeteners or artificially sweetened beverages, and so the likely scenario is that it’s really the sum of all of them together.”

Researchers also found that those who limited their daily intake of ultra-processed foods by more than three servings per day had a lower overall risk. 

Future Impact

The study results could help create more opportunities for doctors to talk with their patients about what a healthy diet means and to advise them to consider limiting ultra-processed foods, said another study author, Andrew Chan, MD, a professor of medicine at Harvard Medical School and also a gastroenterologist at Massachusetts General Hospital.

The research may also present a chance for patients who have a mood disorder to consider changing their diet as “another way they can approach their illness,” he said.

The World Health Organization has also advised avoiding artificial sweeteners.

“I think I would feel pretty comfortable counseling a patient to try to avoid ultra-processed foods, especially in the context that they’ve been linked with a lot of other health conditions,” Mehta said.

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