on June 15, 2026
Anxiety Does Not Originate Solely in the Brain
Anxiety and stress are currently among the most widespread conditions in the general population. Although they are often interpreted exclusively as psychological phenomena, modern research shows that they involve a much broader biological network integrating the brain, gut, immune system, metabolism, and endocrine system.
Stress was defined by Hans Selye as the non-specific response of the organism to environmental stimuli, capable of activating adaptation mechanisms and maintaining homeostasis. However, when this response becomes chronic, a condition of neuroendocrine and inflammatory dysregulation may arise.
In recent years, particular interest has emerged in the so-called microbiota–gut–brain axis, a bidirectional communication system that connects the intestinal environment, immune function, and central nervous system activity.
The microbiota–gut–brain axis: a new perspective on mental health
The gut microbiota includes trillions of microorganisms that participate in digestion, immunity, metabolism, and the production of biologically active metabolites.
Increasing evidence suggests that the microbiota may also influence mood and the stress response through several mechanisms:
immune modulation
production of neuroactive metabolites
regulation of the vagus nerve
influence on neurotransmitter synthesis
modulation of the hypothalamus–pituitary–adrenal axis
In animal models, alterations in microbiota composition have been associated with changes in the stress response and anxious behavior. It has also been observed that animals lacking microbiota show a more intense neuroendocrine response to stress, with increased ACTH and corticosterone.
Serotonin and the gut: much more than a brain neurotransmitter
Serotonin is one of the neurotransmitters most involved in the regulation of mood, sleep, and emotional response.
Contrary to popular belief, a very significant portion of the body's serotonin is produced in the gut by enterochromaffin cells in the gastrointestinal mucosa.
The microbiota may contribute indirectly to serotonergic regulation through metabolites derived from fermentation and the modulation of tryptophan metabolism.
However, it should be emphasized that the role of intestinal serotonin and its direct impact on human mood represent an area of research that is still evolving.
BDNF, neuroplasticity, and chronic stress
Another key molecule is Brain-Derived Neurotrophic Factor (BDNF), a neurotrophin involved in neuronal survival, synaptic plasticity, and learning processes.
Reduced levels of BDNF have been observed in several studies of individuals with depression and chronic stress.
Experimental models suggest that intestinal inflammation may be associated with reduced hippocampal BDNF and that certain changes in the microbiota may influence its expression.
These data support the hypothesis of a biological relationship between gut health and brain function.
Neuroinflammation, cortisol, and persistent stress
Chronic stress prolongs the activation of the hypothalamus–pituitary–adrenal axis, leading to increased cortisol production.
When the system remains persistently active, the following may occur:
mental fatigue
reduced concentration
irritability
mood alterations
poorer stress tolerance
Research also suggests that chronic inflammatory processes and metabolic alterations may contribute to the persistence of neuropsychiatric symptoms.
Diet and mental health: is there a relationship?
Diet does not replace medical treatment for psychiatric disorders, but it is a factor that may help maintain neurobiological balance.
Among the most studied elements are:
dietary proteins as a source of tryptophan
omega-3 fatty acids for neuronal structure and function
magnesium for neurochemical metabolism
B vitamins
iron
polyphenols and plant compounds
Several observational studies associate a diet rich in plant-based foods, whole grains, legumes, high-quality protein sources, and unsaturated fats with better mental health outcomes.
Phytotherapy and an integrated approach
In phytotherapy, several plant substances have been studied for their potential to support mood and the stress response.
Among those most extensively investigated in the literature are:
St. John's wort for the support of mild–moderate depressive disorders
saffron for stress and mood
certain probiotic formulations currently under research as so-called psychobiotics
Phytotherapy does not replace medical or psychological treatment but can be incorporated into integrated health strategies.
Anxiety and stress are not exclusively mental phenomena.
Neurotransmitters, the gut–brain axis, the microbiota, nutrition, inflammation, and endocrine regulation all work together to maintain psychophysical balance.
Understanding these mechanisms is opening increasingly integrated perspectives on the prevention of and support for mental well-being.
Bibliography
Selye H. A syndrome produced by diverse nocuous agents. Nature. 1936.
Cryan JF, Dinan TG. Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nat Rev Neurosci. 2012.
Clarke G et al. Gut microbiota and the serotonergic system. Mol Psychiatry. 2013.
Mayer EA, Knight R, Mazmanian SK et al. Gut microbes and the brain. J Neurosci. 2014.
Kelly JR et al. Breaking down the barriers: the gut microbiome and psychiatric disorders. Front Cell Neurosci. 2015.
Foster JA, McVey Neufeld KA. Gut–brain axis. Trends Neurosci. 2013.
Young SN. How to increase serotonin in the human brain. J Psychiatry Neurosci. 2007.
Ng QX et al. A systematic review of probiotics and depression. Neuropsychiatr Dis Treat. 2018.
