A large Australian study has linked high consumption of ultra-processed – or industrially produced – foods to depression.
Medical News Today reports that the NOVA classification categorises foods by the extent and purpose of industrial processing into four categories, from the least to the most processed.
Group one includes unprocessed or minimally processed foods, such as fresh, frozen, or dried fruits and vegetables, whole grains, nuts, whole cuts of meat and fish, eggs, milk, and natural yogurt. These foods are altered by processes “designed to preserve natural foods, to make them suitable for storage, or to make them safe or edible or more pleasant to consume”.
Ultra-processed foods make up group four, “industrial formulations typically with five or more and usually many ingredients, […] [which] often include those also used in processed foods, such as sugar, oils, fats, salt, antioxidants, stabilisers, and preservatives”.
“Ingredients only found in ultra-processed products include substances not commonly used in culinary preparations, and additives whose purpose is to imitate sensory qualities of group 1 foods or of culinary preparations of these foods, or to disguise undesirable sensory qualities of the final product,” according to the the definition.
Ultra-processed foods and mental health
Now, the large-scale study in Australia has found that people who eat a high proportion of ultra-processed foods have a much higher risk of depression than those who eat the least. The research is published in the Journal of Affective Disorders.
The study looked at 15 years of data from more than 23 000 people in the Melbourne Collaborative Cohort Study, a survey looking at the effect of diet and lifestyle on chronic disease risk.
At the outset, none of the participants was taking medication for depression or anxiety.
The researchers divided the cohort into quartiles based on what proportion of their energy intake came from ultra-processed foods.
For those in the highest quartile, 37.1% by mass of their diet came from ultra-processed foods, providing almost half of all their energy intake. Those in the lowest quartile ate on average 15.9% by mass (30.8% by energy).
After adjusting for socio-demographic characteristics, lifestyle, and health-related behaviours, the researchers found those in the highest quartile for ultra-processed food consumption were 23% more likely to show “elevated psychological distress”, a marker for depression, at follow-up.
How does it affect the brain?
Dr Melissa Lane, from the Institute for Mental and Physical Health and Clinical Translation (IMPACT), Food & Mood Centre, School of Medicine at Deakin University and corresponding author of the study, notes:
“Even after accounting for factors like smoking and lower education, income, and physical activity, which are linked to poor health outcomes, the findings show greater consumption of ultra-processed food is associated with a higher risk of depression.”
Ultra-processed foods are generally high in carbohydrates, saturated fat, and energy, and low in protein and fibre.
All of these are likely to increase inflammation, which has been linked to depression and other mental health issues.
They are also often low in micronutrients like vitamins B12, vitamin D, vitamin E, niacin, pyridoxine, copper, iron, phosphorus, magnesium, selenium, and zinc.
These factors can have an impact on mental health, said Dr Eamon Laird, a visiting research fellow at Trinity College, Dublin, Ireland, who was not involved in the study.
“The authors are correct in stating that some ultra-processed foods are high in fat and low in micronutrients. For example, we know vitamin D, B vitamins, and amino acids are essential for optimal mental health in helping prevent depression. This is through different mechanisms such as reduced inflammation, less oxidative damage, improvements in gut microbiota, etc.”
Recent research has focused on the gut-brain axis, with many studies showing the effect of the gut microbiota on mental health.
Many of the foods people eat daily are ultra-processed, even some that are marketed as healthy.
They include:
- carbonated soft drinks and sweetened juices
- sweet or savoury packaged snacks
- chocolate, sweets, and ice cream
- mass-produced packaged breads, buns, cookies, pastries, and cakes
- margarine and other spreads
- breakfast cereals (and cereal bars)
- pre-prepared pies and pasta and pizza dishes
- poultry and fish “nuggets” and “sticks”, sausages, burgers, hot dogs, and other reconstituted meat products, and
- powdered and packaged instant soups, noodles, and desserts.
Research has raised concerns about the effect of a diet high in these foods, with ultra-processed food consumption linked to many health conditions.
As well as increasing the risk of obesity, itself a risk factor for many health conditions, ultra-processed food has been linked to a raised risk of all-cause mortality and cardiovascular disease, colorectal cancer, and death from all cancers, but particularly breast and ovarian cancer.
How diet affects mental and brain health
Increasingly, research is showing the effect of diet on not only physical, but also mental health – a healthy diet, like the Mediterranean diet, for example, is associated with a reduced risk of depression.
Conversely, a less healthy diet, or typical Western diet high in ultra-processed foods, is linked to cognitive decline and mental health issues.
A recent study found that people who ate the most ultra-processed foods had a 28% faster rate of cognitive decline than those who ate the least.
If a typical Western diet, high in ultra-processed foods, can increase the likelihood of depression, can a healthful diet, high in wholegrain, fruit, vegetables, and fresh foods decrease the likelihood of mental health issues?
The answer appears to be “yes.”
A Mediterranean diet, for instance, encourages a healthy gut microbiome, which in turn has a positive effect on both depression and anxiety.
Study details
High ultra-processed food consumption is associated with elevated psychological distress as an indicator of depression in adults from the Melbourne Collaborative Cohort Study
Melissa Lane, Mojtaba Lotfaliany, Allison Hodge, Adrienne O'Neil, Nikolaj Travica, Felice Jacka, Tetyana Rocks, Priscila Machado, Malcolm Forbes, Deborah Ashtree, Wolfgang Marx.
Published in Journal of Affective Disorders on 15 August 2023
Abstract
Background
Few studies have tested longitudinal associations between ultra-processed food consumption and depressive outcomes. As such, further investigation and replication are necessary. The aim of this study is to examine associations of ultra-processed food intake with elevated psychological distress as an indicator of depression after 15 years.
Method
Data from the Melbourne Collaborative Cohort Study (MCCS) were analysed (n = 23,299). We applied the NOVA food classification system to a food frequency questionnaire (FFQ) to determine ultra-processed food intake at baseline. We categorised energy-adjusted ultra-processed food consumption into quartiles by using the distribution of the dataset. Psychological distress was measured by the ten-item Kessler Psychological Distress Scale (K10). We fitted unadjusted and adjusted logistic regression models to assess the association of ultra-processed food consumption (exposure) with elevated psychological distress (outcome and defined as K10 ≥ 20). We fitted additional logistic regression models to determine whether these associations were modified by sex, age and body mass index.
Results
After adjusting for socio-demographic characteristics and lifestyle and health-related behaviours, participants with the highest relative intake of ultra-processed food were at increased odds of elevated psychological distress compared to participants with the lowest intake (aOR: 1.23; 95%CI: 1.10, 1.38, p for trend = 0.001). We found no evidence for an interaction of sex, age and body mass index with ultra-processed food intake.
Conclusion
Higher ultra-processed food intake at baseline was associated with subsequent elevated psychological distress as an indicator of depression at follow-up. Further prospective and intervention studies are necessary to identify possible underlying pathways, specify the precise attributes of ultra-processed food that confer harm, and optimise nutrition-related and public health strategies for common mental disorders.
See more from MedicalBrief archives:
Cancer threat raised by ultra-processed foods – UK-led study
US studies show colorectal cancer link to ultra-processed foods
Ultra-processed food linked to cognitive decline – Brazilian study
NHS assesses studies on mortality risk of ultra-processed foods