on June 18, 2026
The brain does not live in isolation: emotions, metabolism and the internal environment
For many years, mental well-being has been interpreted almost exclusively through the functioning of brain neurotransmitters. Anxiety, mental fatigue, mood changes or loss of motivation were often attributed mainly to imbalances in serotonin, dopamine or noradrenaline.
Today, the picture has become more complex.
Modern knowledge in the fields of neurobiology, nutrition and psychoneuroendocrinoimmunology (PNEI) shows that the brain functions within a complex network in which diet, gut microbiota, immune system, sleep-wake rhythm, physical activity and stress management contribute to determining psychological well-being.
Among the main players in this balance are serotonin and cortisol.
Serotonin: much more than the so-called “happiness hormone”
Serotonin is a neurotransmitter involved in the regulation of:
mood
sleep quality
appetite
motivation
pain sensitivity
cognitive processes
eating behavior
It is important to remember that serotonin is not simply “taken in” with food.
Its synthesis depends on the availability of tryptophan, an essential amino acid obtained through diet.
The main dietary sources of tryptophan include:
eggs
fish
legumes
soy
nuts
dairy
whole grains
Serotonin production also depends on the presence of metabolic cofactors, including:
vitamin B6
folates
vitamin B12
magnesium
iron
A monotonous or unbalanced diet can reduce the efficiency of these processes.
The gut produces serotonin: what does this really mean
One of the most interesting discoveries in recent years concerns the role of the gut.
About 90% of the body's serotonin is produced by enterochromaffin cells in the gut.
This fact is often interpreted in a simplistic way.
Gut serotonin does not enter the brain directly by crossing the blood-brain barrier.
However, the gut microbiota can indirectly influence the nervous system through:
tryptophan metabolism
production of short-chain fatty acids
activation of the vagus nerve
immune regulation
modulation of systemic inflammation
For this reason, diet and gut health are now considered important components of mental well-being.
Cortisol: when the stress hormone stops being useful
Cortisol is produced by the adrenal glands and is essential for:
regulating energy and blood sugar
promoting adaptation to stress
coordinating the immune response
maintaining the circadian rhythm
The problem is not cortisol itself.
The problem arises when stress becomes chronic.
Excessive activation of the hypothalamus-pituitary-adrenal axis can be associated with:
insomnia
agitation
reduced concentration
mood changes
increased perception of fatigue
increased emotional hunger
In the long term, elevated cortisol levels can alter tryptophan metabolism, reducing its availability for the synthesis of serotonin and melatonin.
Diet and stress: the role of low-grade inflammation
Modern diet can contribute to creating a biological environment conducive to maintaining stress.
An excess of:
refined sugars
ultra-processed foods
sugary drinks
highly processed fats
can be associated with chronic low-grade inflammation.
This state has been studied in relation to:
changes in neuroplasticity
microglia activation
reduced insulin sensitivity
increased vulnerability to stress
Conversely, dietary patterns rich in plant-based and minimally processed foods have been associated with better indicators of mental health.
Nutrients involved in neurochemical well-being
Proteins and amino acids
Adequate protein intake provides the precursors for numerous neurotransmitters.
Tryptophan → serotonin
Phenylalanine and tyrosine → dopamine and noradrenaline
Omega-3
Omega-3 fatty acids are structural components of neuronal membranes.
They have been studied for their role in:
supporting neuroplasticity
inflammatory modulation
cognitive well-being
The main dietary sources include oily fish, oilseeds and nuts.
Magnesium
Magnesium participates in hundreds of enzymatic reactions.
It has been studied for its involvement in stress regulation and nervous system physiology.
The main sources are:
whole grains
legumes
nuts
cocoa
green vegetables
B vitamins
B vitamins contribute to the metabolic processes involved in energy production and neurotransmitter synthesis.
Physical activity changes the brain
Regular physical activity is one of the non-pharmacological interventions with the strongest evidence.
Exercise helps to:
modulate cortisol
improve insulin sensitivity
increase neurotrophic factors such as BDNF
promote sleep
improve mood
Even moderate activity performed regularly shows benefits.
Sleep, light and biological rhythms
Sleeping little or irregularly alters:
cortisol secretion
glucose metabolism
microbiota activity
emotional regulation
Exposure to natural light in the morning and maintaining regular hours helps synchronize circadian rhythms.
Phytotherapy and integrated approaches: what the research says
Several phytocomplexes have been studied to support mental well-being.
Those of greatest scientific interest include:
saffron
lavender
bacopa
St. John's wort
It is important to remember that plant extracts do not replace medical treatments and that some substances, such as St. John's wort, can interact with numerous medications.
The role of emotions and lifestyle
Mental well-being does not arise from a single food or a single neurotransmitter.
Social relationships, stress management, quality of rest, diet and movement build the biological context in which the brain works every day.
Mental health is the result of a dynamic balance.
Conclusions
Serotonin and cortisol represent two central nodes in the physiology of adaptation.
Through diet, physical activity, sleep quality and gut care, we can influence many of the biological systems involved in mental well-being.
The goal is not to pursue a single miracle nutrient, but to build an environment conducive to the body's resilience.
Bibliography
Firth J et al. The effects of dietary improvement on symptoms of depression and anxiety: meta-analysis of randomized controlled trials. Psychosom Med. 2019.
Jacka FN et al. A randomised controlled trial of dietary improvement for adults with major depression (SMILES trial). BMC Med. 2017.
Marx W et al. Diet and depression: exploring biological mechanisms. Mol Psychiatry. 2021.
Cryan JF, O’Riordan KJ et al. The microbiota–gut–brain axis. Physiol Rev. 2019.
Clarke G et al. Gut microbiota and the serotonergic system. Int J Neuropsychopharmacol. 2013.
Calder PC. Omega-3 fatty acids and inflammatory processes. Nutrients. 2017.
Miller AH, Raison CL. The role of inflammation in depression. Nat Rev Immunol. 2016.
Donelli D et al. Effects of lavender on anxiety: systematic review and meta-analysis. Phytomedicine. 2019.
Lopresti AL, Drummond PD. Saffron and mood disorders. Hum Psychopharmacol. 2014.
