Research has long suggested a connection between our diet and our mental health. The gut microbiome—the shared genome of the trillions of bacteria that live in the gut, largely shaped by what we eat and drink—appears to influence how we feel and think.

But there are not enough human studies to identify what bacteria are, even if they are important.

That is slowly changing. The largest analysis of depression and the gut microbiome, published in December, found that many types of bacteria were increased or decreased in people with symptoms of depression.

“This study provides some empirical evidence that you are what you eat,” said study author Andre Utterlinden, who conducted the genetics study at the Erasmus Medical Center in Rotterdam, the Netherlands.

Or to be more precise, how you feel is closely related to what you use.

The gastrointestinal system has been featured in brain research for centuries. In the early 1800s, prominent London physician John Abernethy said, “Constipation” was the root of all mental illness.

And often there are gastrointestinal symptoms reported People with mental illness. Changes in weight and appetite are common among people with depression Adolescence to the Old age. Anxiety has been Attached to. High risk of nausea, vomiting, diarrhea and constipation. The connection between food and emotion exists even when we reach for macaroni and cheese to comfort us in stressful times.

Interest in the gut-brain axis has experienced a resurgence in the past 20 years. Many studies have pointed to a connection between the microbiota in our gut and our brains, including ours. Memory, Feeling And Cognitive skills.

Such research has led to probiotics, prebiotics and everything fermented. as scientific names Bacteroidetes And Lactobacillus, Two of the most common bacteria found in healthy people have become household words.

The best foods to feed your gut microbiome

The health trend is a little ahead of the evidence. Most of the research linking depression and the gut, for example, has been done in animals and few studies have included human participants.

Still, the evidence so far points to a connection between the two. An interesting one Research, titled “Transmission of the Blues,” showed that bacteria-free mice with stool samples from people with severe depression were anxious and less interested in pleasurable activities. Their metabolism is related to tryptophan, a chemical Depression, has changed. But the mechanics behind the microbe-mood pathway — and which bacteria are important — have been hard to pin down.

Bacteria that predict symptoms of depression

This new study moves that needle, mostly due to size. The investigators, led by Najaf Amin, who studies population health at the University of Oxford, analyzed data from the Rotterdam Study, a decades-long effort to understand the health of local populations.

Amin and her colleagues focused on this phase of the study, which involved collecting stool samples from more than 1,000 people. These participants self-reported depression using a 20-item assessment.

The researchers analyzed the relationship between bacteria in stool samples and depression assessment scores. They then conducted similar experiments using data from 1,539 other Dutch citizens of different ethnicities. (Confirming findings from one large cohort in a second, larger cohort makes them particularly reliable.)

The analysis revealed 16 types of bacteria that the authors called “significant predictors” of different levels of depressive symptoms. for example, The studyPublished in natural relationships, found exhaustion Eubacterium ventriosum Among depressed people. Interestingly, this same reduction was observed in microbiological studies. Traumatic brain injury And Excessive obesityThey are both Arrested to the DepressionSupporting the idea that this bacterial species has something to do with this mood disorder.

Migrants arrive with thriving gut microbes. Then the American diet throws them garbage.

The study authors also attempted to answer the big question: Does any particular gut flora cause depression? It’s a tricky idea. Major depressive disorder has been linked to more than 80 different genetic mutations, all of which are weak.

“There is no single gene that causes depression,” said Jane Foster, a professor of psychiatry at UT Southwestern who studies the gut-brain connection and was not involved in this study.

There is no technology that can clearly prove the cause. So the researchers turned to a tricky statistical calculation called Mendelian randomization, which can tease out the direction of the effect when the gene-disease association is strong. This is not the case with depression, which makes the calculations here interesting, but not necessarily useful.

Still, the calculations indicated many bacteria: Eggerthella – In people with depression, they can be symptoms of depression. The discovery did not surprise Amin.

Eggerthella“Anxious people have a constant increase in the gut,” she says. The results provide evidence that changes in gut flora can cause symptoms of depression. “We cannot exclude our own DNA as a contributing source,” Foster said. “It’s a combination of the DNA you were born with, your life experiences to date, and your environment.”

Plants can cause depression or, on the contrary, be close to the point. “The cause is not a one-way street,” said Jack Gilbert, who directs the Center for Microbiome and Metagenomics at the University of California, San Diego, and was not involved in the new study.

Instead, the gut and brain cycle together. For example, comfort eating after a stressful event appears to alter the microbial community in our gut, which can exacerbate depression.

Clearly, Gilbert says that when we are depressed, the gut microbiome often lacks beneficial flora. “If we can add those nutrients back in, maybe we can reactivate that cycle,” Gilbert said.

Changing your diet to improve your mood

This is where nutrition comes into the picture. An individual who doesn’t consume enough fiber, for example, may have reduced butyrate-producing bacteria, Amin said, which can lead to symptoms of anxiety and inflammation and possibly depression.

It may sound pessimistic that the message from all this work is to eat more fruits and vegetables, not more sugar. But more research proving the power of a healthy gut has become undeniable even to the most serious skeptics, Gilbert adds.

“When the evidence suggests that eating healthy, getting a little exercise, and taking mental breaks show benefits, we should listen to that information,” he says.

Eating fiber changes the microbiome. It may also increase cancer treatment.

Research is slowly unraveling exactly how bacteria communicate with the brain. For example, many produce short-chain fatty acids such as butyrate and acetate Influence Brain activity. Others produce a chemical called GABA, which is also deficient Connected. to the Depression.

This improvement means that diet may not be the only way to improve our intestinal colonies. While the use of probiotics to prevent and treat depression may be an exact science, eventually leading to effective alternatives to antidepressants, Gilbert says, there is still a stigma in many communities.

Foster said profiling the bacteria could help identify people at risk for depression. Her lab is looking for clues among the gut flora that might help someone with depression.

All of this research has convinced Utterlinden that there is only one significant side effect of adopting a gut-boosting diet. “You’ll be happier,” he said.

Have a question about healthy eating? email EatingLab@washpost.com And we will answer your question in the next column.

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