As the well-known phrase “you are what you eat” suggests, what we consume has far-reaching effects. Along with the foods we eat, we also consume bacteria that can make up what is known as microbiota, or the microorganisms that inhabit our gastrointestinal tract and other bodily surfaces. As Dr. Jane Foster explains, scientists have discovered a link between microbiota and anxiety-like behaviors in animal models and in humans..1
One research group, Neufeld et al., examined mice raised in a germ-free environment against those raised under typical conditions. After allowing both groups of mice to explore an elevated plus maze, the germ-free mice spent more time in the open arms indicated a reduced level of anxiety-like behavior in germ-free mice.2 Interestingly, in other studies, mice given beneficial bacteria in the form of probiotics had reduced anxiety-like and depression-like behavior.
Now taking these principles and applying them to human subjects, Messaoudi and colleagues (2011) conducted a double-blind, placebo-controlled, randomized study where healthy volunteers received a mixture of probiotic supplements of L. helveticus and B. longum for 30 days.3
The team assessed individuals using several clinical questionnaires including the Hopkins Symptom Checklist, the Hospital Anxiety and Depression Scale, the Perceived Stress Scale, and the Coping Checklist. After receiving the probiotic mixture, individuals showed reduced general signs of anxiety and depression in addition to a decrease in stress hormone, cortisol, levels over time.
Expanding on this research, Tillisch and colleagues4 gave healthy individuals a fermented milk product with or without probiotics for 28 days. The probiotic mixture included Bifidobacterium animalis subsp. lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis subsp. lactis. The researchers were able to determine, using Functional magnetic resonance imaging (fMRI), that individuals that consumed the probiotic mixture had altered brain activity in resting state and a reduced response to an emotional-recognition task.
Unfortunately, developing a connection between intestinal bacteria and behavior is only the beginning. The next step is to seek to find out what mechanisms are involved. Dr. Foster suggests microbiota may be targeting immune signaling, various neural pathways, altering neurotransmitter levels and gene expression in the CNS, and intestinal permeability.1
Dr. Foster highlights more clinical work is needed to directly examine the microbiota-gut-brain axis in individuals with depression and anxiety disorders. In particular, she recommends a comprehensive analysis of immune markers, gut function and brain activity, in both healthy individuals and those with mood and anxiety disorders. She posits this understanding may help improve anxiety and depressive-related symptoms.
1. Foster, J. “Microbes and the Mind” Culture, Volume 35 Number 3 | ISSN 09650989
2. Neufeld KM, Kang N, Bienenstock J, Foster JA (2011) “Reduced anxiety-like behavior and central neurochemical change in germ-free mice.” Neurogastroenterol Motil 23:255–64–e119.
3. Messaoudi M, et al. (2011) “Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects”. Br J Nutr 105:755–764
4. Tillisch K, et al. (2013) “Consumption of fermented milk product with probiotic modulates brain activity”. Gastroenterology 144:1394– 401–1401.e1–4.