The connection of the gut and the brain is a topic that has fascinated medical researchers almost from the dawn of organized medical thought. Second century Greek physician Galen, whose work underpinned much of Western medical thought really up to the advent of the microscope, had much to say on the subject, believing that certain foods gave rise to beneficial or harmful humors, and certain herbs or fermented products such as yogurt could regulate these humors in the gut.
The whole idea of humorism has been passé for centuries. But Galen, who entirely lacked an appreciation of the microscopic world but was nonetheless brilliant in the detail of his observations and the power of his insight, was groping in the right direction. Mental states and the decisions that arise from these and are expressed as behaviors, are interrelated with the makeup and activity of the gut microbiome to a degree that is only now being fully appreciated.
Becoming a convert
Dr Emeran Mayer, director of the Oppenheimer Center for the Neurobiology of Stress at the University of California Los Angeles, spoke on the subject of the gut brain axis at the recent Probiota Americas event in San Diego that was hosted by NutraIngredients-USA.
“This has been a topic that has fascinated me throughout my career. It was a fringe area for many years, I would say decades. If if I had to pick one area as clearly the recognition that the gut microbiome was a huge player in the gut-brain axis,” Mayer said.
Mayer said he had been skeptical of probiotics research earlier in his career because he thought a number of the studies had not been carefully done. But he accepted an unrestricted grant from a probiotic company to do research on the topic. He was given freedom to design a study looking at a four week probiotic intervention and what effect that had on brain response. He was convinced going into it that the result would be negative and would serve mostly to characterize the placebo effect. To his surprise, his study among health women showed a statistically significant effect on brain activity in the regions that control the processing of emotion and sensation. Mayer said follow-up studies have confirmed the effect, and have led him to infer that gut microbial makeup early in life has a big effect on structural effects seen in adults.
“In some ways it has completely changed the trajectory of my career,” he said.