Consuming large amounts of ultraprocessed foods may be linked to depression, research published Wednesday found.
Ultraprocessed foods are high in salt, sugar, hydrogenated fats and additives. They include quintessential junk food items such as chips and soda, but also a lot of ready-to-eat meals, yogurts and packaged bread.
The study, published in the journal JAMA Open Network, looked at the eating habits and mental health status of more than 31,000 women between the ages of 42 and 62. The participants came from the Nurses’ Health Study II, a long-running observational study group, and were almost entirely white.
The researchers found that women who ate the most ultraprocessed food — nine servings per day — were 50% more likely to develop depression than those who ate the least, no more than four servings a day. Consuming a high amount of foods and drinks that contained artificial sweeteners had a particularly negative effect, the study found.
Melissa Lane, a postdoctoral researcher at the Food and Mood Centre at Deakin University in Victoria, Australia, said that the new research “supports other observational studies across the globe that have found higher intakes of ultraprocessed food are associated with a higher risk of developing depression.”
What sets the study apart from other research that has compared eating ultraprocessed foods to mental health is that the researchers started the study before the participants reported any symptoms of depression and then followed them over time. This allowed them to make a stronger connection between a person’s diet and their risk of developing depression. A limitation, however, was that the study included very few nonwhite women and no men, which makes it difficult to apply the findings to everyone.
Lane, who was not involved with the new research, said it’s still unclear why there is a link between ultraprocessed foods and depression.
It can also be difficult to determine which came first: the diet or the depression.
“We don’t have a lot of energy when we are feeling depressed,” said Susan Albers, a clinical psychologist at the Cleveland Clinic who was not involved with the new study, “so it’s easy to reach for those foods when we are low energy and don’t have motivation to cook or to grocery shop — just open a package and they are ready to go.”
The study was not a clinical trial, so it cannot show that eating ultraprocessed foods caused depression, but Albers said other research has shown the opposite to be true as well: eating whole foods, full of essential nutrients including fiber, vitamins and minerals, is linked to good mental health.
There are some clues as to how ultraprocessed food may affect the gut, which has been shown to be closely linked to the brain, she added.
“There is emerging evidence that ultraprocessed food may actually disrupt the normal gut microbiome,” said study co-author Dr. Andrew Chan, the chief of the clinical and translational epidemiology unit at Massachusetts General Hospital in Boston.
People who eat a lot of these foods tend to have a gut that is more pro-inflammatory, which may cause the gut microbiome to release molecules that influence risk for depression, Chan said.
Albers said another possible explanation for the link between ultraprocessed foods and depression focuses on artificial sweeteners. Artificial sweeteners may cause a process called purinergic transmission, in which the brain doesn’t release the right amount of a chemical called ATP, she said. ATP binds with other molecules in the brain — notably the so-called feel good chemicals serotonin and dopamine — to send messages between neurons. This disruption causes inflammation in the brain and is one reason experts think ultraprocessed foods may be linked to depression.
If researchers one day prove ultraprocessed food does increase the risk of depression, the finding could offer possible help for those with the condition.
“This may be a particularly important notion for people who have depression because it may be a relatively easy way to prevent both depression and longer term problems that could be more difficult to deal with,” Chan said.
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