An analysis of data from the Melbourne Collaborative Cohort Study showed that individuals who consumed a high amount of ultra-processed food were more likely to experience psychological distress, an indicator of depression, more than a decade later. The link remained even after adjusting for sociodemographic characteristics, lifestyle, and health-related behaviors. The study was published in the Journal of Affective Disorders.
Depression is a mood disorder characterized by persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in activities. It often involves changes in appetite, sleep patterns, energy levels, and concentration. Individuals with depression may experience physical symptoms like fatigue, as well as cognitive symptoms like negative self-perception and difficulty making decisions. It is one of the most frequent mental health disorders worldwide.
Numerous factors contribute to the severity of depressive symptoms, but recently, researchers have been particularly interested in a possible connection between poor diet quality and depression. If this link is confirmed, it could be especially significant because diet is a more easily modifiable factor than many other depression predictors.
Research has often focused on the link between ultra-processed foods and poor mental health, with the relationship appearing to be bidirectional. Ultra-processed foods are industrially manufactured, heavily processed products that often contain additives, artificial flavors, and high levels of sugars, fats, and salt, while providing limited nutritional value.
Study author Melissa M. Lane and her colleagues wanted to know whether consumption of ultra-processed foods early in life, between 13 and 17 years of age, is linked to depression later in life. They analyzed data from the Melbourne Collaborative Cohort Study, an Australian longitudinal study aiming to investigate associations between lifestyle and chronic non-communicable diseases.
The researchers note that previous studies have not been able to produce very firm conclusions about links between poor mental health and ultra-processed food consumption because the consumption of this type of food varies greatly between countries. While less than 10% of calories are derived on average from such foods in the Mediterranean countries, this percentage is above 40% in Australia, U.S., U.K., and Canada.
The Melbourne study mitigates this problem by including a large share (30%) of immigrants from Southern Europe (i.e., Mediterranean). Dietary preferences of these individuals are markedly different from those of participants born in Australia and New Zealand. The study is also longitudinal, allowing researchers to observe the links between studied factors over years.
The researchers analyzed data from 23,299 participants (13,876 women) aged between 27 and 76 years, excluding those unsuitable for the analysis. The study had an intentional overrepresentation of immigrants from Southern Europe, allowing a better comparison of dietary habits between these participants and Australians.
The researchers collected data on participants’ dietary intake habits using a questionnaire designed for this study (the 121-item Food Frequency Questionnaire) at the start of the study, between 1990 and 1994. They also used data on participants psychological distress (the Kessler Psychological Distress Scale), which they considered an indicator of depression. This assessment asks participant about symptoms such as fatigue, hopelessness, nervousness, sadness and worthlessness. The participants completed the assessment of psychological distress between 2003 and 2007 i.e., more than a decade later.
Food items were classified into ultra-processed and non-ultra-processed categories. Ultra-processed foods included items like soft drinks, sweet or savory packaged snacks, confectionery, packaged breads, margarine, reconstituted meat products, and pre-prepared frozen or shelf-stable dishes. Non-ultra-processed foods encompassed rice, cereals, meat, fish, milk, eggs, fruit, roots and tubers, vegetables, nuts and seeds, culinary ingredients like sugar and plant oils, and processed foods such as breads, cheese, canned fruit and fish, and salted and smoked meats.
The results showed that participants most prone to ultra-processed food consumption were more likely to be born in Australia and New Zealand and to live alone. They were less likely to have a tertiary education, be married or in a relationship, and engage in high levels of physical activity. These individuals also had lower intake of protein, fiber, and saturated fats and lower total energy intake. They ate fruits and vegetables less often.
Participants with the highest levels of ultra-processed food consumption (the top 25% in terms of ultra-processed food intake) had a 14% higher likelihood of experiencing psychological distress compared to those in the lowest 25% of ultra-processed food intake. Further analysis revealed that only participants in the highest consumption group had elevated psychological distress levels compared to other participants.
“In this Melbourne-based cohort of 23,299 participants, higher consumption of ultra-processed food at baseline was associated with elevated psychological distress, as a marker for depression, at 15 years follow-up. However, this association was evident only among participants with very high consumption of ultra-processed food; that is, those in the highest quartile. Further prospective (with relevant data at all time-points), mechanistic and intervention research is needed to better identify the harmful attributes of ultra-processed food, and to inform nutrition-related and public health strategies for mental health,” the study authors concluded.
The study sheds light on the links between dietary intake and mental health. However, it should be noted that the study design does not allow for any cause-and-effect conclusions to be drawn. Additionally, the psychological distress assessment asked only about depression and anxiety symptoms in the 30 days prior to the survey, while the assessment of dietary intake was based on participants’ recall of their typical dietary habits in the preceding 12 months. This left lots of room for recall and self-report bias.
The study, “High ultra-processed food consumption is associated with elevated psychological distress as an indicator of depression in adults from the Melbourne Collaborative Cohort Study”, was authored by Melissa M. Lane, Mojtaba Lotfaliany, Allison M. Hodge, Adrienne O’Neil, Nikolaj Travica, Felice N. Jacka, Tetyana Rocks, Priscila Machado, Malcolm Forbes, Deborah N. Ashtree, and Wolfgang Marx.