Long-term consumption of ultra-processed foods may increase depression risk

By Hugo Francisco de SouzaSep 25 2023Reviewed by Lily Ramsey, LLM

In a recent study published in the JAMA Network Open Journal, researchers used a long-term, large cohort study design to evaluate the effects of ultra-processed food (UPF) on mental health.

Study: Consumption of Ultraprocessed Food and Risk of Depression. Image Credit: Daisy Daisy/Shutterstock.com

Background

Their results suggest that UPFs, especially artificially sweetened beverages, significantly increase depression risk in middle-aged Hispanic women.

Reducing UPF intake by at least three daily servings partially rescued study participants from depression risk. However, additional research would be required to verify this finding and elucidate the degree of risk reduction.

Ultra-processed foods and health

As suggested by the age-old phrase “you are what you eat,” diet is one of the most important modifiable treatments individuals can harness to improve their health and well-being.

Unfortunately, an alarming trend in recent decades is a shift from fresh and minimally processed foods to ‘fast-foods,’ highly modified diets, appealing to taste but of poor nutritional value. Recent evidence suggests that consuming these dietary products may have a detrimental effect on not only physical but also mental health.

‘Ultra-processed foods’ (UPFs) is a relatively novel classification of foods under the NOVA classification system. These foods are made from extracts of fats, starches, added sugars, and hydrogenated fats.

They may also contain additives like artificial colors and flavors or stabilizers. These foods include frozen meals, soft drinks, hot dogs and cold cuts, fast food, packaged cookies, cakes, and salty snacks.

A growing body of research has flagged UPFs as directly responsible for human diseases, including irritable bowel syndrome, obesity and overweight, reduced immune response, and cancer. However, research into the mental health impacts remains scant.

Of the few available studies in the field, most suffer from a lack of long-term data, small cohort sizes, or a limited ability to overcome potential confounders in observed data.

The increasing ubiquity of mental health diseases worldwide makes identifying their risks essential, especially when these risks are behavioral and easily adjustable.

About the study

In the present study, researchers used a sizeable female cohort obtained from the Nurses’ Health Study II, a joint sample group from the Harvard T.H. Chan School of Public Health and the Brigham and Women’s Hospital.

The long-term study was conducted between 2003 and 2017, with follow-ups every four years. The sample cohort comprised 31,712 individuals between the ages of 42 and 62 (mean 52), all of whom did not have clinical depression symptoms at study initiation.

This study’s methodology complied with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines.

Data collection involved using validated food frequency questionnaires (FFQs) with clinical mental health assessments at study initiation and every subsequent four years.

UPF intake was quantified by first defining UPF in adherence to the NOVA classification of the food category. UPF diets were further classified into their constituent components for additional model evaluation power, each of which was analyzed separately.

These included ultra-processed grain foods, ready-to-eat meals, sweet snacks, fats and sauces, savory snacks, ultra-processed dairy products, artificial sweeteners, processed meat, and beverages.

“We used 2 definitions for depression: (1) a strict definition requiring self-reported clinician–diagnosed depression and regular antidepressant use and (2) a broad definition requiring clinical diagnosis and/or antidepressant use.”

Cox proportional hazard models were used to compute hazard ratios (HRs) and class intervals (95% CI) for depression using UPF consumption quintiles.

To avoid model bias and control for confounding variables, known and suspected depression risk factors, including age, caloric intake, body mass index (BMI), physical activity levels, menopausal hormone therapy, smoking status, total energy intake, alcohol consumption, median family income, marital status, and sleep quality, were adjusted during model testing.

Depression comorbidities like diabetes, hypertension, and dyslipidemia were also accounted for in analyses.

To ascertain if UPF consumption outcomes were reversible, researchers finally analyzed individuals who reduced their UPF consumption between successive four-year follow-ups and those whose consumption remained relatively stable.

Study findings

Results from this study establish a direct association between higher UPF consumption and increased risk of depression, as indicated by hazard ratios of 1.49 (2,122 individuals) and 1.34 (4,840 cases) for the strict and broad definitions of UPFs, respectively.

Individuals with high UPF consumption also showed an increased prevalence of other unhealthy behaviors, including smoking, low physical activity levels, high BMI, and depression comorbidities, specifically diabetes, hypertension, and dyslipidemia.

Adjusting models for potential confounding variables did not significantly alter study results. Surprisingly, no direct association could be made between age, BMI, physical activity, or smoking and increased depression risk.

“In a 4-year lag analysis, associations were not materially altered (strict definition: HR, 1.32; 95% CI, 1.13-1.54; P < .001), arguing against reverse causation.”

UPF component analyses revealed that artificially sweetened beverages and artificial sweeteners were directly associated with depression risk, while other component associations were non-significant.

Finally, the exploratory analyses revealed that a reduction in UPF intake by three servings per day was able to partially rescue participants from depression risk, compared to participants who maintained a relatively stable UPF consumption pattern.

“These findings suggest that greater UPF intake, particularly artificial sweeteners and artificially sweetened beverages, is associated with increased risk of depression. Although the mechanism associating UPF to depression is unknown, recent experimental data suggests that artificial sweeteners elicit purinergic transmission in the brain, which may be involved in the etiopathogenesis of depression.”