Common food additive may impact gut bacteria, increase anxiety

A wide range of foods contain ingredients that we call emulsifiers. A new study in mice shows that these compounds can produce both physiological and behavioral changes.

Bread and butter — Bread and spreads commonly contain emulsifiers.

Food additives have always generated a great deal of attention, and, rightly so, as they are all-pervasive, so we should scrutinize their impact on our health. Recently, emulsifiers have been drawing fire.

Manufacturers use these chemicals to alter food’s texture and extend its shelf life.

They include emulsifiers in many foods, for instance, some types of bread, chocolate, margarine, processed meats, and more.

Earlier studiesTrusted Source have shown that emulsifiers can alter the microbiome of mice, causing low-grade inflammation and increasing the risk of obesity and metabolic disorders.

A studyTrusted Source in humans concluded that gut bacteria “can be directly impacted by these commonly used food additives, in a manner that subsequently drives intestinal inflammation.”

Recently, a group of researchers from Georgia State University in Atlanta took this investigation to the next level, setting out to investigate whether two common emulsifiers — carboxymethylcellulose (CMC) and polysorbate-80 (P80) — might also influence mental well-being.

Gut health, psychological health

Although the jump from gut health to psychological health might seem like a stretch, scientists have already described a clear, two-way conversation between the gut and the brain.

Studies have shown that our gut health and the health of our gut bacteria can have a substantial influence on our mental well-being. For instance, one study from 2011 found that treating mice with Lactobacillus rhamnosus — a species of “good” bacteria — caused measurable changesTrusted Source in the brain and reduced anxiety-like behavior.

Another studyTrusted Source showed that mice that had no gut bacteria express higher levels of anxiety-like behaviors when researchers compared them with controls. A more recent studyTrusted Source showed that antibiotic use in mice in early life could significantly alter the microbiome, anxiety levels, and social behavior over the long-term.

This most recent study investigated whether P80 and CMC might alter the mental state of mice. The researchers publishedTrusted Source their findings in the journal Scientific Reports.

The team added CMC and P80 to the drinking water of mice for 12 weeks. Then, they measured their behavior, changes in their microbiome, and other physiological parameters.

Co-lead researcher Prof. Geert de Vries explains their work in brief, “We asked the question: Can emulsifiers’ effects on general systemic inflammation also be extended to the brain and to behavior? The answer was yes.”

The impact of emulsifiers

The scientists showed that the emulsifiers did impact gut bacteria, but in different ways for male and female mice. They also showed that the changes in behavior were different between the sexes.

Specifically, they saw an increase in anxious behavior, particularly in male mice. In female mice, there was a reduction in social behavior.

Exactly how emulsifiers might affect behavior is not known, but there are some theories.

“[W]e know that inflammation triggers local immune cells to produce signaling molecules that can affect tissues in other places, including the brain. The gut also contains branches of the vagus nerve, which forms a direct information pathway to the brain.”

Prof. Geert de Vries

Why there should be sex differences is harder to explain. However, scientists know that there are certain differences between the way male and female immune systems work, so this might offer clues.

The group plan to continue this line of investigation. Switching from the mouse model into larger animals will be a necessary move, as the authors write, “determining the extent to which studies in mice are relevant to humans is inherently difficult,” particularly in behavioral disorders.

Co-lead researcher Benoit Chassaing says, “We are currently investigating the mechanisms by which dietary emulsifiers are impacting the intestinal microbiota as well as the human relevance of those findings.”

It is also worth noting that, of the four anxiety tests, emulsifier-fed male mice only showed significant differences in one. The test in question was the open field test and, according to the authors, research suggests it is particularly sensitiveTrusted Source at measuring “normal” anxiety, as opposed to anxiety disorders.

Over recent years, many observers have noted a rise in anxiety in Western society. At the same time, inflammatory bowel disease has shown a marked increaseTrusted Source. The authors ask whether food additives might play a part in these shifts.

For now, the researchers recommend that we should assess food additives for their impact on gut bacteria. Science has now shown, beyond a shadow of a doubt, that the microbiome plays a significant role in health; perhaps food safety laws need to follow suit.

Could this chemical help explain anxiety?

A recent study on anxiety examined the role of glutamate, which is a neurotransmitter. The findings could help scientists develop more effective interventions.

Anxious young woman — A new study digs into the neuroscience of anxiety.

Almost everybody experiences anxiety in one of its forms.

Over time, evolution honed anxiety as a survival mechanism; it forms part of our “fight-or-flight” response.

The heart pumps a little faster, and there might be a sensation of nausea as the body prepares for action.

Although anxiety is a natural response, it can spiral out of control for some people.

Rather than being a protective force that helps us navigate everyday life, it becomes a burden that impacts well-being. Also, being more prone to anxiety increases the risk of developing an anxiety disorder and depression.

Beyond mental health, anxiety might also have physical effects; the authors of the new study write that sustained high levels of anxiety “may increase the risk of developing cardiovascular disease.”

The Anxiety and Depression Association of America say that anxiety disorders impact almost 1 in 5 adults in the United States each year.

Anxiety disorders are as commonTrusted Source as depression, but until relatively recently, they received much less attention.

Because of its growing prevalence, the neurological mechanisms that are involved are receiving increased attention. The latest study, which now appears in The Journal of Neuroscience, investigates the role of glutamate in the hippocampus.

What is glutamate?

Glutamate is an amino acid and the primaryTrusted Source excitatory neurotransmitter in the brain. In recent years, studiesTrusted Source have hinted that glutamate might be involved in anxiety.

Reductions in glutamate activity seem to increase anxious behavior, and glutamate levels within the hippocampus — which is the part of the brain primarily involved in regulating emotions and memory — seem particularly important.

Earlier studies have also concluded that two other regions of the brain work with the hippocampus to modulate anxiety; called area 25 and area 32, these regions form part of the prefrontal cortexTrusted Source.

However, our understanding of glutamate’s role in anxiety is not fully formed — other studies have produced conflicting results.

As an example, a study using nonanxious rats found that a reduction of activity at some glutamate receptor subtypes in the hippocampus actually reducedTrusted Source levels of anxiety.

The authors of the latest study wanted to examine the role of glutamate in anxiety in more detail. To get a clearer picture, they ran a series of experiments on marmosets.

Glutamate and anxiety in primates

First, the team tested each marmoset’s anxiety levels when introduced to an unfamiliar human (one of their handlers wearing a mask). As expected, the animals with the greatest levels of anxiety — or high-trait anxiety — had significantly lower levels of glutamate in their hippocampus.

High-trait anxiety correlated with glutamate levels in the right anterior hippocampus.

Next, they artificially increased the level of glutamate in the highly anxious marmosets. They found that once glutamate levels reached normal levels, the animals responded less anxiously in psychological tests.

This second arm of the experimentation gave the researchers evidence of a causal relationship: Anxious primates naturally had lower levels of glutamate activity, and when glutamate was increased in the anxious primates’ hippocampi, anxiety was reduced.

To gain more information about the role of brain areas 25 and 32, the team carried out further experiments.

Blocking activity in these regions, they found that the anti-anxiety effects of increasing glutamate were abolished when area 25 was out of action. Blocking area 32, however, did not make a difference.

The study authors suggest that the hippocampal-area 25 pathway could be an interesting target for future pharmaceutical interventions. Overall, the authors outline their conclusions:

“These findings provide casual evidence in primates that hippocampal glutamatergic hypofunction regulates endogenous high-trait anxiety, and the hippocampal-area 25 circuit is a potential therapeutic target.”

Though scientists are still unpicking glutamate’s role in anxiety, studies such as this bring us closer to having a full understanding.