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(CNN) -- Consuming large amounts of ultra-processed foods and beverages, especially if they are artificially sweetened, may be linked to the development of depression, according to a new study.

"The study suggests a link between ultra-processed food consumption and depression, with an approximately 50% higher risk for those who consume 9 servings (a day) or more (20% higher) compared to those who consume 4 servings or less," says Gunter Kuhnle, Professor of Food Science and Nutrition at the University of Reading. United Kingdom. Kuhnle was not involved in the study.

Ultra-processed foods include soups, sauces, frozen pizzas, convenience foods, and pleasure foods such as hot dogs, sausages, chips, soda, store-bought cookies, cakes, candy, doughnuts, ice cream, as well as many more foods and beverages containing artificial sweeteners.

"Our study focused on the relationship between food and the subsequent risk of developing a new episode of depression," said study co-author Dr. Andrew T. Chan, the Daniel K. Podolsky Professor of Medicine at Harvard Medical School and Professor of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health. in Boston.

• Ultra-Processed Foods Linked to Deaths from Ovarian and Other Cancers: Study

Ultra-processed foods include hot dogs, sausages, chips, soda, store-bought cookies, cakes, candy, ice cream, and many foods that contain artificial sweeteners. (Credit: happy_lark/iStockphoto/Getty Images)

"However, there is also the possibility that for people with chronic depression, ultra-processed foods may worsen their condition," says Chan, who is also chief of the Clinical and Translational Epidemiology Unit at Massachusetts General Hospital in Boston.

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When the researchers looked at specific ultra-processed foods, also known as UPFs, foods and beverages made with artificial sweeteners were associated with an increased risk of depression among the people studied, who were all women, Kuhnle said.

"This is an interesting finding because it suggests that the relationship between UPF intake and depression is due to a single factor: artificial sweeteners," he said.

What's the link?

Why are these foods associated with the onset of depression? First, there is a known link between ultra-processed foods and chronic inflammation, according to Chan.

Inflammation is one of the root causes of many chronic diseases. For example, studies have linked ultra-processed foods to colorectal cancer in men and to heart disease and premature death in both men and women.

"Literally hundreds of studies link ultra-processed foods to obesity, cancer, cardiovascular disease and overall mortality," Marion Nestle, the Paulette Goddard Professor Emeritus of Nutrition, Food Studies and Public Health at New York University, told CNN in a 2022 interview.

A 2014 study found a link between soda and light fruit drinks and depression. People who used artificial sweeteners in coffee and tea were also more likely to develop depression, according to the study.

There is also a link with dementia. If more than 20 percent of a person's daily calories come from ultra-processed foods, the risk of cognitive decline increases by about 28 percent, according to a 2022 study. For a 2,000-calorie-a-day diet, that would be 400 calories: by comparison, a small order of fries and a regular McDonald's cheeseburger together contain a total of 530 calories.

"There's also a link between ultra-processed foods and altered gut microbiome," Chan says. "This is an important potential mechanism linking ultra-processed foods to depression, as there is emerging evidence that gut microbes have been linked to mood through their role in metabolism and the production of proteins that have activity in the brain."

• Study Links Cognitive Decline to Consumption of Ultra-Processed Foods

Association, not cause-effect

The study, published Wednesday in the journal JAMA Network Open, examined the diets of nearly 32,000 middle-aged women who are part of the Nurses' Health Study II, a longitudinal study of women's health. The study did not include any men, so the results cannot be generalized.

What's more, the study is observational, meaning researchers can only find an association between the onset of depression and intake of ultra-processed foods. Therefore, the study cannot account for the possibility of a phenomenon known as "reverse causation," said Dr. David Katz, a specialist in preventive and lifestyle medicine, who was not involved in the study.

"To the extent that sweet drinks and ultra-processed foods offer acute, if fleeting, 'comfort,' it is also plausible that the early discomforts of incipient depression motivate greater reliance on precisely those foods," Katz said. "In this construct, depression generates a higher intake of UPF, and not the other way around."

It's also possible that depression and increased intake of "junk" and "comforting" foods "feed off each other," said Katz, who founded the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.

"Early depression is likely to compromise dietary moderation and increase intake of 'comforting' and 'junk' foods. The degradation of mood could then further degrade the diet, and a spiral of degeneration occurs," he says.

It's also difficult to separate any impact of diet on depression risk compared to other known risk factors, such as a family history of depression, high levels of stress and lack of a supportive social network, Dr. Paul Keedwell, a consultant psychiatrist and fellow of the Royal College of Psychiatrists, said in a statement. Keedwell was not involved in the study.

The researchers controlled for other possible causes of depression, such as age, body mass index (BMI), total calories, menopausal hormone therapy, alcohol consumption, sleep duration, pain and other diseases, such as diabetes and hypertension.

"The list of factors associated with UPF consumption, such as higher BMI, more smoking and less exercise, highlights how many confounding factors there may be," Keith Frayn, emeritus professor of human metabolism at the University of Oxford, said in a statement. Frayn was not involved in the study.

"Nonetheless, the authors seem to have adjusted them as carefully as possible, and the relationship between artificial sweeteners and depression stands out clearly," Frayn said.

"This adds to growing concern about artificial sweeteners and cardiometabolic health," he added. "The relationship with depression needs confirmation and more research to suggest how it might occur."

Depression