Do gut bacteria control your mind?

August 20, 2014

The relationship between gut bacteria and unhealthy eating (credit: UC San Francisco)

Bacteria within you — which outnumber your own cells about 100 times — may be affecting both your cravings and moods to get you to eat what they want, and may be driving you toward obesity.

That’s the conclusion of an article published this week in the journal BioEssays by researchers from UC San Francisco, Arizona State University and University of New Mexico from a review of the recent scientific literature.

How your gut microbiome may control you

  • The diverse community of microbes, collectively known as the gut microbiome, influence human eating behavior and dietary choices to favor consumption of the particular nutrients they grow best on, rather than simply passively living off whatever nutrients we choose to send their way.
  • Some bacterial species prefer fat, and others sugar, for instance. They vie with each other for food and to retain a niche within their ecosystem — your digestive tract — and they also often have different aims than you do when it comes to your own actions.
  • Bacteria may influence your decisions by releasing signaling molecules into your gut. Because the gut is linked to the immune system, the endocrine system, and the nervous system, those signals could influence your physiologic and behavioral responses — and health.
  • Bacteria may be acting through the vagus nerve, which connects 100 million nerve cells from the digestive tract to the base of the brain, changing taste receptors, producing toxins to make you feel bad, and releasing chemical rewards to make you feel good.
  • Certain strains of bacteria increase anxious behavior (in mice).
  • Some strains of bacteria cause stomach cancer and perhaps other cancers.

What you can do (with medical guidance)

  • Make changes in what you eat. There are measurable changes in the microbiome within 24 hours of diet change, evolving on the time scale of minutes.
  • Take appropriate probiotics. One study showed a drink containing Lactobacillus casei improved mood in those who were feeling the lowest.
  • Kill targeted species with specific antibiotics.
  • Acquire specialized bacteria that digest your favorite foods. (Bacteria that digest seaweed are found in humans in Japan, where seaweed is popular in the diet.)
  • See previous KurzweilAI posts on gut bacteria

The co-authors’ study was funded by the National Institutes of Health, the American Cancer Society, the Bonnie D. Addario Lung Cancer Foundation, and the Institute for Advanced Study in Berlin.

Abstract of BioEssays paper

Microbes in the gastrointestinal tract are under selective pressure to manipulate host eating behavior to increase their fitness, sometimes at the expense of host fitness. Microbes may do this through two potential strategies: (i) generating cravings for foods that they specialize on or foods that suppress their competitors, or (ii) inducing dysphoria until we eat foods that enhance their fitness. We review several potential mechanisms for microbial control over eating behavior including microbial influence on reward and satiety pathways, production of toxins that alter mood, changes to receptors including taste receptors, and hijacking of the vagus nerve, the neural axis between the gut and the brain. We also review the evidence for alternative explanations for cravings and unhealthy eating behavior. Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating.