Gut Feeling: Curing the Mind Through the Stomach?


The endocrinologist Dr. Mark Lyte suggested that gut microbes speak to the brain using their own neurotransmitters. Gut bacteria produce and respond to the same chemicals the brain uses to govern mood (for example, serotonin, dopamine, and GABA). Presumably, the brain might monitor — and react to — “gut feelings” in order to control outside influences. Probiotics may alleviate anxiety by producing anti-inflammatory molecules, such as serotonin, or reducing activity of the hypothalamic-pituitary-adrenal axis, a set of organs whose interaction helps regulate stress.

Treating The Gut To Treat The Brain

The beneficial effects of prebiotics and probiotics on digestive health in humans are well-known. However, there are not too many studies on how they affect the brain.

One research team, led by the neuroscientist Dr. Philip Burnet at the University of Oxford, tested the effects of prebiotics on anxiety in 45 healthy adults. Prebiotics are carbohydrates (fibers) that feed beneficial bacteria already found in the gut. Participants received either a prebiotic supplement or placebo every day for three weeks. The results were published in the journal Psychopharmacology.

“People who are depressed tend to focus on negative information,” says Burnet. To test emotional processing, the researchers performed several computerized assessments, such as eliciting responses to positive and negative words. “After using prebiotics people focused more on positive stimuli than negative information,” says Burnet. Saliva cortisol levels were also lower in the prebiotic group than in controls, indicating diminished anxiety.

The reduction in anxiety is likely due to the anti-inflammatory effects of gut bacteria, according to Burnet. The gut responds to stress or infection by releasing inflammatory cytokines, these in effect disturb brain chemistry and increase susceptibility to anxiety or depression. Prebiotics may increase bacterial diversity, which alters the gut ecosystem and helps put out the fire. “The results suggest prebiotics could work on mechanisms that affect mental health,” Burnet says.

A study published in Brain, Behavior, and Immunity, led by psychologist Dr. Laura Steenbergen from the Leiden Institute of Brain and Cognition in the Netherlands, investigated the potential effects of probiotics on depression. For four weeks, 40 healthy participants received either a multistrain probiotic or placebo.

“Rumination is one of the most predictive vulnerability markers of depression,” said Steenbergen in a statement. “Persistent ruminative thoughts often precede and predict episodes of depression.” At the end of the study, the probiotic users had fewer negative thoughts than the placebo group, suggesting that beneficial bacteria have the power to brighten up a dark mood.

Probiotics have also been linked to activation of certain brain areas. A study published in the journal Gastroenterology by Dr. Kirsten Tillisch and colleagues used functional MRI to measure changes in resting brain activity and emotion recognition. They gave 36 healthy women probiotics twice daily for four weeks. Twelve consumed a probiotic yogurt, 11 had a nonprobiotic yogurt, and 13 received no intervention. The fMRI results showed that probiotics led to reduced reactivity in the brain regions associated with anxiety (including the insula and somatosensory cortex) in response to images of angry or frightened faces. Their research was an important step in demonstrating the influence of gut health on brain circuitry.

Perhaps one day a drug remedying the gut could treat the brain? Most scientists agree it’s too soon to tell. “Probiotics and prebiotics offer a natural option without the side effects of drugs that target the brain, but it is unlikely that they will replace traditional therapies,” cautions Burnet. “They could improve brain function overall, and therefore improve the response to a drug in treatment-resistant patients.”

Good for Your Gut — And Head

  • Probiotics: kimchi, some yogurts, kefir, tempeh, olives
  • Prebiotics: asparagus, garlic, endive, wheat, oats
  • Anti-inflammatories: ginger, turmeric, fish oil, cayenne, green tea

This article is updated from its initial publication in Brain World Magazine’s Fall 2015 issue.

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