Study indicates that ultra-processed foods are linked to depression

By Dr. Liji Thomas, MDReviewed by Danielle Ellis, B.Sc.Feb 14 2023

Highly processed foods, also called ultra-processed foods (UPFs), are widely recognized as predisposing to various medical conditions due to their adverse impact on metabolic pathways. However, less is known about their effect on mental health. A recent research paper explored this aspect, showing a positive association in younger Italians between UPF intake and depressive symptoms, which could point the way for further research in this field.

Study: Ultra-Processed Food Consumption and Depressive Symptoms in a Mediterranean Cohort. Image Credit: Lightspring / Shutterstock

Introduction

Many illnesses are linked to poor dietary quality, including cardiovascular and metabolic diseases, obesity, and some cancers. Young people seem at the highest risk for such disorders because of constant exposure to attractive, freely available, and cheap UPFs, coupled with a stressful lifestyle that promotes sedentary habits and little sleep.  

UPFs are a NOVA category of foods “characterized by formulations containing few or no natural ingredients, supplemented with chemical additives and preservatives to prolong shelf life, but also supply intense palatable features and properties (i.e., flavor enhancers, colorants, emulsifiers, artificial sweeteners, thickeners, and foaming/anti-foaming agents).”

This detailed description is necessary to show how market-oriented researchers have come up with foods that are very unhealthy but are paradoxically in great demand among youngsters, who lack the training and maturity to control their impulses, deny their cravings, or delay their gratification.

While UPFs may comprise up to a fifth of daily energy intake in Mediterranean countries, this proportion rises to as high as 80% in highly Westernized populations like the US, Canada, and Australia. Recent research indicates that the health risks of UPFs are not associated with their poor nutritional quality alone.

The current paper, published in the journal Nutrients, looks at UPFs in relation to depressive symptoms in a group of younger Italian adults. The data came from the Mediterranean healthy Eating, Aging and Lifestyle (MEAL) study, which investigated the linkage between lifestyle behaviors and non-communicable diseases in Mediterranean countries.

All participants came from Catania, Italy. The study included 735 people below the age of 35 years. Food frequency questionnaires (FFQ) were used to capture the consumption of over a hundred foods and beverages.

What did the study show?

The scientists found that unmarried and physically active individuals had a higher average consumption of UPFs. Conversely, a high UPF intake was linked to significantly moving away from the Mediterranean diet (MD), characterized by natural foods, including whole grains, nuts, dairy, legumes, olives, grapes, and other fruit, vegetables, and fish, with wine and olive oil.

The highest UPF intake was associated with increased consumption of micronutrients and sodium, as well as higher total consumption of food and processed food. In contrast, this group had significantly lower consumption of fruits, cereals, vegetables, legumes, dairy, and olive oil, which are prominent in the MD.

Notably, the highest UPF intake was associated with twice as high a chance of depressive symptoms after compensating for energy intake. This remained the same even when adjusting for factors like age, sex, occupation, smoking, and physical activity. When MD adherence was considered, those with the highest UPF intake were almost three times as likely to have depressive symptoms.

What are the implications?

The findings of this study suggest that high UPF consumption is linked to higher odds of depressive symptoms. This holds true even when the nutritional quality of the diet is accounted for.

The MD is a proxy for a healthy diet. Yet, following it more closely failed to compensate for increased UPF intake and instead increased the chances for depressive symptoms. This indicates that other dietary components affect the impact of UPFs on mental health.

This corroborates earlier research showing that depressive symptoms increased by a fifth when UPF consumption increased by a tenth in a French cohort, while the risk of depression went up by a third when the average UPF intake increased. Other studies from the USA and Brazil also showed similar associations.

Younger people may be more at risk because of work stresses, having less free time coupled with limited financial stability. This may lead to their choosing convenient, tasty, and cheap UPFs rather than natural foods.

The association may be due to the high concentration of refined sugars and saturated and trans fats in many UPFs. Increased energy density could upset the finely tuned physiology of the body, causing metabolic dysregulation and cellular impairment. The final outcome could be cell and tissue breakdown and death.

Some mechanisms through which this operates could be oxidative stress due to high sugar levels within cells, which enhances glucose oxidation pathways causing impaired mitochondrial function. In addition, high fatty acid levels stress the endoplasmic reticulum, damaging cellular membrane systems while activating oxidative and inflammatory pathways at the gene level.

UPFs are notoriously low in fiber, which could also cause the breakdown of normal regulatory mechanisms by disrupting the gut microbiome. This could cause immune dysregulation, the impairment of gut barrier integrity, and the passage of bacteria into the circulation, leading to systemic inflammation. This also could activate gut-brain neural pathways that indirectly affect brain neurotransmitters.

In addition, the impact of dysbiosis on the gut peptides and hormones produces a range of effects on the brain. The interconnected levels of these may reinforce unhealthy cravings for junk foods like UPFs, with binge eating and poor self-control. This may explain the association with depressive symptoms.

Furthermore, food additives that are found in plenty in UPFs cannot be ignored as they may cause neural damage and dysbiosis, uncoupling the relationship between caloric intake and gut responses, promoting gut inflammation and oxidative stress. All of these result in poor health and increase the risk of depression and impaired cognition via direct and indirect neural toxicity.

“The findings from this study do not necessarily imply that UPFs must necessarily cause depression, but that UPFs might be consumed as comfort foods by an at-risk population (i.e., younger individuals with emerging mood disorders), and that it can establish a vicious cycle by further enhancing detrimental effects on brain health related to depression.”

Future studies are required to validate and extend this association and tease out the specific roles played by non-nutritional components in the mental health risk presented by UPFs.