It’s slowly changing. The largest-ever analysis of depression and the gut microbiome, published in December, found that several types of bacteria were either significantly elevated or decreased in people with symptoms of depression.
“This study provides real evidence that it’s what you eat,” said study author André Uterlinden, who studies genetics at the Erasmus Medical Center in Rotterdam, the Netherlands.
Exactly how you feel is closely related to what you consume.
The gastrointestinal system has been featured in brain research for centuries. In the early 1800s, John Abernethy, a popular London physician, believed that “stomach upset” was the root of all mental disorders.
Gastrointestinal symptoms are also commonly reported in people with mental illness. Changes in weight and appetite are common in depressed patients from adolescence to old age. Anxiety is linked to increased risk of nausea, heartburn, diarrhea and constipation. Whether it’s macaroni or cheese that calms you down during a stressful time, the connection between food and mood is there.
Interest in the gut-brain axis has revived over the past two decades. Many studies point to a connection between the microbiome that inhabits our intestinal tract and our mind, including our memory, mood, and cognitive abilities.
Research like this has spawned an industry that ferments probiotics, prebiotics, and everything. bacteroides When lactic acid bacteria, The two most common bacteria found in healthy humans have become a common term.
Health trends are a little ahead of the evidence. For example, most of the studies linking depression to the gut have been done in animals, with only a small number of studies involving human participants.
Yet the evidence so far points to a link between the two. In one notable study, entitled “Transferring the Blues,” germ-free rats given stool samples from humans diagnosed with major depression became anxious and disinterested in pleasurable activities. Altered metabolism of tryptophan, a chemical associated with depression. However, it has been difficult to clarify the mechanisms behind microbial mood pathways and which bacteria are at fault.
Bacteria that predict depressive symptoms
This new study moves that needle, mainly because of its size. 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 specifically on this phase of the study, which involved collecting fecal samples from more than 1,000 people. These participants also provided a self-report of their depression using a 20-item rating.
Researchers analyzed data for associations between bacterial populations in stool samples and scores on depression assessments. She then conducted the same test using data from another of her 1,539 Dutch citizens, including various ethnicities. (Findings from one large group are particularly reliable when validated with her second large group.)
The analysis revealed 16 types of bacteria that the authors called “significant predictors” of depressive symptoms to varying degrees. for example, Nature Communications, found depletion of Eubacterium ventriosum in depressed people. Interestingly, this same reduction was found in microbiome studies of traumatic brain injury and obesity, both associated with depression, supporting the idea that this type of bacteria is associated with this mood disorder. I support you.
The study authors were also challenged to answer the big question. Do specific gut microbiomes cause depression? That’s a tough proposition. Major depressive disorder is associated with over 80 different genetic variants, all of which are weak.
“There’s no gene that causes depression,” says Jane Foster, a professor of psychiatry at UT Southwestern University who studies the gut-brain connection and was not involved in the study.
No technology exists to clarify causality. So researchers turned to a clever statistical calculation known as Mendelian randomization. This can lead to the direction of influence when genes and diseases are strongly related. This is not the case for depression, which makes the calculations here interesting, but not necessarily useful.
Still, calculations showed that one bacterium was present in abundance — Eggerterra — People with depression as the cause of their symptoms of depression. This discovery did not surprise Amin.
Eggerterra, she said, “is found to be consistently and abundantly increased in the gut of depressed individuals. This result provides evidence that alterations in the gut microbiota can cause depressive symptoms.” “We cannot rule out our own DNA as a contributing source,” says Foster. “It’s a combination of your DNA, your life experiences, and your environment.”
Whether flora causes depression or vice versa may be out of the question. said he was not involved in the new study.
Rather, the gut and brain circulate together. For example, it appears that eating comfort after a stressful event can alter the microbial community in the gut, which in turn can exacerbate feelings of depression.
What’s clear, says Gilbert, is that our gut microbiome is often deprived of beneficial flora when we’re depressed. , we might be able to reinvigorate that cycle,” says Gilbert.
change your diet to feel better
This is where dining comes into the picture. For example, people who don’t consume enough fiber may experience a decrease in butyrate-producing bacteria, leading to stress and inflammation, and potentially symptoms of depression.
You may feel disappointed that the message from all this work is to eat lots of fruits and vegetables and not too much excess sugar. The sheer volume of research has made even the most ardent skeptics undeniable, including Gilbert.
“If the evidence points to the fact that eating healthy, exercising a little, and taking mindfulness breaks is beneficial, then you should probably listen to the data,” he says.
Research reveals exactly how bacteria interact with the brain. For example, many of them produce short-chain fatty acids such as butyrate and acetate, which affect brain activity. Others produce a chemical called GABA, a deficiency of which has been linked to depression.
This advance means diet may not be the only way to improve gut colonization. , which may eventually lead to effective alternatives to antidepressants.
Bacterial profiling could also help identify people at risk for depression, Foster said. Her lab looks for signs in the gut flora that indicate which drugs might work best for people suffering from depression.
All this research has convinced Uitterlinden that there is only one major side effect of adopting a gut-enhancing diet. “You will be happier,” he said.
Questions about healthy eating? Email EatingLab@washpost.com I may answer your question in a future column.
