Do ultra-processed foods impact mental health?

Over recent years, scientists have linked diets high in ultra-processed food to several health issues, including high cholesterol, cardiovascular disease, and cerebrovascular disease — a group of conditions including stroke. 

Worryingly, nutrient-light ultra-processed foods are on the rise in the United States.

In 2018, children aged 2–19 got 67% of their energy from ultra-processed foods. In the same year, ultra-processed foods accounted for 57% of adults’ energy intake.

Globally, the amount of ultra-processed foods in a diet varies between countries, and the U.S. and United Kingdom are the top consumers.

But other regions are catching up fast, particularly in South and Southeast Asia, the Middle East, and North Africa. 

Evidence is also mounting that ultra-processed foods might impact mental health. Here, we’ll focus on its links to depression and anxiety. 

Before we dive in, let’s recap on processed and ultra-processed foods.

Processed versus ultra-processed

Processed foods are foods that have been changed from their natural state. Often, this means that manufacturers have added ingredients such as salt, sugar, and oil. 

These foods may also have been pasteurized, heated, or dried. They include bread, fruit juice, plain bran cereal, rice, pasta, canned fish, vegetables, and fruits. 

In other words, most of the food that you eat has been processed, but that’s not necessarily bad, per se — not all processes make food more unhealthy. For instance, milk is pasteurized to kill off potentially dangerous germs.

Ultra-processed foods go one step further. Manufacturers create these from compounds extracted from other foods, like starches, sugars, and fats. Food manufacturers also tend to add other ingredients such as stabilizers, artificial colors, and flavorings.

If you aren’t sure whether something is ultra-processed, this is a good rule of thumb: 

If the label lists many ingredients and you don’t recognize most of the names, it’s probably ultra-processed. A high fat, sugar, and salt content is another giveaway.

At ZOE, we know a diverse diet filled with fresh foods is best. No foods are off the table, but some — like ultra-processed foods — are best enjoyed only occasionally. Our research has also shown that everyone responds differently to foods.

Using our at-home test, we can identify how your blood sugar and blood fat levels respond to different foods. We will also analyze your gut microbiome — the trillions of bacteria and other microbes in your gut. 

Using this data, we can provide you with personalized nutrition advice to ensure you are eating the best foods for your unique body.

You can take our free quiz today to find out more.

Ultra-processed foods and depression

According to the World Health Organization (WHO), depression affects around 1 in 20 people globally — it’s a leading cause of disability.

Current treatments can help, but they are limited. Finding more effective ways to treat or prevent depression is urgent, and some scientists are investigating dietary interventions.

Studies have already identified that what we eat influences our mental health. For instance, a review and meta-analysis of multiple studies concluded that a healthy diet — with a high intake of fruit, vegetables, fish, and whole grains — was associated with lower odds of depression.

Another meta-analysis concluded that a Western diet might increase the risk of depression, while a healthy diet may reduce the risk. But what about ultra-processed foods, specifically?

The NutriNet-Santé study, which has been running since 2009, is an internet-based nutrition study that set out to identify links between nutrition, health, lifestyle factors, and mortality.

In 2019, the team published research that looked for links between ultra-processed foods and depressive symptoms. The authors included data from 20,380 participants in France who they followed for an average of 5.4 years.

Even after taking into account a range of factors, they concluded that consuming more ultra-processed food was linked to an increased likelihood of experiencing depressive symptoms.

A study in Spain generated similar results. The researchers followed 14,907 university graduates for an average of 10.3 years. 

Rather than measuring depressive symptoms as they did in the NutriNet-Santé study, the authors focused on the use of antidepressant medications and diagnoses of depression.

Overall, the authors identified an association between increased consumption of ultra-processed foods and the risk of depression. They also note that the risk of depression was strongest in people who exercised the least.

Why the link?

In the NutriNet-Santé paper, the authors outline a few reasons why ultra-processed foods might be linked to depressive symptoms.

They suggest that some compounds in ultra-processed foods — like emulsifiers or chemicals produced during high-temperature heating — might be partly to blame.

These compounds might, they explain, alter the gut microbiome. As a result, they could cause an imbalance, which experts call dysbiosis.

Over recent years, evidence has been building that gut bacteria play a role in mental health.

ZOE scientists and their academic collaborators are at the leading edge of gut microbiome research.

We’ve identified 15 “good”  gut bugs linked to positive health markers and 15 “bad” bugs related to negative health markers. 

Our research has also found a link between eating highly processed foods and having more “bad” bugs.

If you’d like to know which gut bacteria you host and how to boost your “good” bugs, take our free quiz today.

A recap on anxiety

Much of the research into ultra-processed food has concentrated on depression or mental health more broadly, but some have also included data on anxiety.

Most of us will have experienced anxiety in some shape or form, for instance, during a stressful work meeting or while waiting for the results of an exam. 

But for some people, this feeling appears without a reasonable cause — and it hangs around. If it repeatedly interferes with everyday life, it could be an anxiety disorder. 

Anxiety disorders affect 19.1% of adults in the U.S. That’s almost 1 in 5 people. So, do ultra-processed foods play a part?

Ultra-processed foods and anxiety

A Brazilian study investigated how fresh and ultra-processed food affected mental health during the COVID-19 pandemic. In all, the scientists recruited 1,693 participants.

The authors found that eating more fresh food was linked to a lower risk of depressive symptoms and anxiety, whereas consuming more ultra-processed foods was associated with increased depressive symptoms and anxiety.

They also identified some interesting links:

“Regarding the consumption of ultra-processed foods, we observed higher daily consumption of instant noodles among those with symptoms of anxiety or depression, and higher daily consumption of soft drinks or artificial juice drinks among those with symptoms of anxiety.”

Another study, this time in Iran, looked at processed foods more broadly rather than ultra-processed foods. The study included 1,782 adults aged 18–35. 

After adjusting their analysis for a range of factors, the authors, again, noted a “significant relationship between increased consumption of processed foods and anxiety.”

Researchers in Norway also ran a study looking at processed foods more broadly. After analyzing data from 5,731 people, the authors reached similar conclusions: “a higher intake of processed and unhealthy foods was associated with increased anxiety.”

A cut and dry conclusion?

Looking at the studies above, it seems clear that ultra-processed foods negatively impact mental health. However, we should also think about the limitations of the research.

One important point is that these types of studies tend to be observational rather than randomized controlled trials. 

In a randomized controlled trial, the researchers might randomly split participants into two groups and house them in a lab where they could monitor them closely. It’s challenging and expensive to run studies like this. 

In an observational study, it’s not possible to prove cause and effect.

As the authors of the NutriNet-Santé study explain, even though they accounted for as many variables as possible — including overall diet, socioeconomic status, and existing health problems — there may have been other factors they couldn’t control for.

Another issue with some of the studies discussed above is that individuals who eat more ultra-processed foods are likely to eat fewer fruits and vegetables.

So, is it the high levels of ultra-processed foods that cause mental health symptoms, or is it the lack of fresh produce?

Another alternative explanation of the results might be that people with depression or anxiety are more likely to choose ultra-processed foods rather than ultra-processed foods causing mental health issues. 

There’s still a lot to unpick, and studies investigating foods and mental health are notoriously tricky — there are so many factors to consider.

What should you do?

Evidence is mounting that ultra-processed foods might negatively impact mental health. And scientists have already noted links between these foods and a range of physical health issues. 

Whether ultra-processed foods cause depression and anxiety or not, it’s sensible to consider your intake.

It’s also important to remember that everyone’s body responds differently to foods. For example, some people experience sizable blood sugar spikes after eating a particular food, while others do not. And the same applies to blood fat levels.

Both blood fat and blood sugar responses are important markers of future health. When you enroll in the ZOE program, our at-home test will measure both of these responses, and we’ll also analyze your gut microbiome. 

Using this information, we will create personalized nutrition advice to help you eat the best foods for your body. Start by taking our free quiz today.