Drugs, Guts, Brains, but Not Rock and Roll: The Need to Consider the Role of Gut Microbiota in Contemporary Mental Health and Wellness of Emerging Adults

Abstract

Emerging adulthood (ages 18-25) is a critical period for neurobiological development and the maturation of the hypothalamic-pituitary-adrenal axis. Recent findings also suggest that a natural perturbation of the gut microbiota (GM), combined with other factors, may create a unique vulnerability during this period of life. The GM of emerging adults is thought to be simpler, less diverse, and more unstable than either younger or older people. We postulate that this plasticity in the GM suggests a role in the rising mental health issues seen in westernized societies today via the gut-brain-microbiota axis. Studies have paid particular attention to the diversity of the microbiota, the specific function and abundance of bacteria, and the production of metabolites. In this narrative review, we focus specifically on diet, physical activity/exercise, substance use, and sleep in the context of the emerging adult. We propose that this is a crucial period for establishing a stable and more resilient microbiome for optimal health into adulthood. Recommendations will be made about future research into possible behavioral adjustments that may be beneficial to endorse during this critical period to reduce the probability of a "dysbiotic" GM and the emergence and severity of mental health concerns.

Keywords: adolescent; emerging adult; environmental exposure; gut–brain–microbiota axis; mental health/ethnology; microbiota.

Figure 2

Common findings for the different types of diet on the gut–brain–microbiome axis. (A) Diets rich in vegetables, fiber, micronutrients such as vitamins D and C, probiotics and prebiotics, fermented foods, anti-inflammatory omega-3-rich, low-fat, and low-carbohydrate foods promote positive mental health and increases in Bacteroidetes, Prevotella, short-chain fatty acids, Bifodobacteria, Akkermansia, Roseburia, Lactilobacillus, and interleukin (IL)-10, and decreases in Firmicutes, Escherichia coli, Ruminococcus, Coprococcus, vascular endothelial growth factor, monocyte chemoattractant protein-1, interferon gamma-induced protein 10, IL-17, IL-12, c-reactive protein, IL-2, tumor necrosis factor, and lipopolysaccharide [49,50,51]. (B) High-fat, high-sugar, and ultra-processed foods increase Bacteroides, bile acids, Bilophila wadsworth, Enterobacteriaceae, Firmicutes, Enterobacteriaceae, Escherichia, Klebsiella, and Shigella [49,52]. Figure created with Biorender (accessed on 29 April 2022).

Figure 1

Interface between the gut microbiota and mental health likely depends upon several factors. (A) The first being the inputs to the intestinal tract which shape the microbiota accordingly (diet, medication, antimicrobials, etc.). (B) Periods where microbiota goes through changes in diversity (alpha) occur in healthy people, especially between late teens and early twenties, which likely result in differences of metabolic output which impact brain health. (C) The intersection of the adolescent brain, combined with a normally fluctuating microbiota of the age group, the promotion of a desirable microbiota through physical activity/exercise and circadian rhythm, and less desirable microbiota using different substances. Part (C) adapted from Bian et al., 2017 [12]. Figure created with Biorender (accessed on 29 April 2022).