Nearly half the calories in the average Canadian diet come from ultra-processed foods.
That’s worrisome considering studies have linked higher intakes of these foods to a greater risk of obesity, non-alcoholic fatty liver disease, asthma, cardiovascular disease, Type 2 diabetes, colorectal cancer and premature death.
Now, new research from Harvard Medical School and the Harvard T.H. Chan School of Public Health points to another good reason to cut back on highly processed foods, especially ones that contain artificial sweeteners.
Doing so, the study suggests, helps guard against depression. Here’s what to know.
What are “ultra-processed” foods (UPFs)?
Simply put, ultra-processed foods contain ingredients you won’t find in your kitchen at home.
They’re formulations of substances derived from foods along with additives used to flavour, sweeten, bleach, colour, emulsify, texturize and preserve. UPFs contains little, if any, real food.
Think chicken nuggets, snack bars, cake mixes, ice cream, ready-to-eat breakfast cereals, sliced breads, frozen waffles, pretzels, soft drinks, processed meats, instant noodles, frozen French fries, frozen pizza and many more.
From a nutritional standpoint, UPFs are typically high in calories, added sugars, unhealthy fats and/or sodium. They’re stripped of gut-friendly fibre, protective phytochemicals and naturally occurring vitamins and minerals.
The NOVA food classification system, which groups all foods based on the extent of their processing, defines UPFs as formulations of ingredients, typically created by a series of industrial techniques.
The link between ultra-processed food and depression
The latest research, published last month in the journal JAMA Network Open, set out to determine the relationship between UPF consumption and the risk of developing depression.
It also aimed to learn if certain types of UPF and/or their ingredients were associated with depression risk.
To do so, the researchers followed 37,712 healthy females, ages 42 to 62 years, for 14 years. Participants did not have depression at the start of the study.
Dietary data was collected every four years to assess intake of UPF as defined by the NOVA classification.
Compared to participants with the lowest intake of UPF (fewer than four servings/day), those who consumed the most (more than nine servings/day) had a 50 per cent higher risk of developing depression during the study.
Other risk factors for depression were controlled for including age, calorie intake, body mass index, physical activity, smoking status, alcohol intake, existing heath conditions, sleep duration, social networks and pain.
The researchers estimated that reducing UPF intake by three servings a day would lower the risk of depression.
When the researchers looked at specific types of UPF and UPF ingredients, only high intakes of artificially sweetened beverages and artificial sweeteners were tied to a greater risk of depression, suggesting that artificial sweeteners drive the association between UPF intake and risk of depression.
The study’s strong points include its large sample size, repeated diet assessments and the ability to control for a number of different potential risk factors for depression.
The researchers were also able to assess participants’ diets several years before the onset of depression, reducing the likelihood of reverse causality (i.e. depression caused participants to eat more UPF).
The study was observational meaning the findings don’t prove that UPF causes depression. They simply show a correlation.
Participants were white females, so the findings can’t be generalized to other groups of people.
Still, the current study adds to growing evidence that eating lots of UPF increases the risk of depression.
How ultra-processed food may harm
Previous research has suggested ways in which UPF can affect mental health.
A diet high in UPF may negatively influence gut microbes, resulting in a less diverse microbiome. This, in turn, can contribute to chronic inflammation.
It’s thought that inflammatory-immune compounds communicate with the brain, affecting mood and energy levels.
There’s also evidence that artificial sweeteners can impair the synthesis and release of serotonin and dopamine, brain chemicals that influence mood.
Cutting back on ultra-processed food
Unless you prepare all your meals and snacks from scratch, it’s impossible to completely avoid UPFs.
The goal is to limit their consumption. Keep in mind, the study linked UPF and onset of depression among people who consumed very high quantities.
Read ingredient lists. Avoid buying foods with long lists that include additives you’d never use at home.
Gradually replace ultra-processed foods with real ones.
Replace highly processed snacks with whole fruit, unsweetened yogurt, nuts and seeds, homemade trail mix, homemade muffins and raw vegetables, for example.
Where possible, make homemade versions of highly processed staples you rely on such as pasta sauce, salad dressings and soups.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on X @LeslieBeckRD