The gut microbiome: how our bacteria influence our health and our mood

At the time I’m writing this article, sunset in England is at 4:12 p.m… a warning for sensitive souls!

As the days grow shorter, our mental health can suffer: less light, more sedentary behaviour and sometimes fewer social interactions create a rather unfavorable mix for our mood. Fatigue, irritability, and a drop in motivation are common, partly due to reduced production of serotonin, a key neurotransmitter involved in mood regulation (1). Some people affected by this drop in serotonin develop Seasonal Affective Disorder (SAD).

The Central Role of the Gut–Brain Axis

The link between the gut and the brain plays an important role in this phenomenon. These two organs communicate via the vagus nerve, a bit like a walkie-talkie where signals travel in both directions. The “butterflies in the stomach” during a first date or the sudden urge to go to the bathroom before a stressful event are perfect examples. Our microbiome produces essential neurotransmitters (serotonin, dopamine, and GABA) that regulate mood and anxiety (2). When the gut flora is imbalanced (dysbiosis) or the intestine becomes too permeable (leaky gut), this production can be disrupted, influencing our mental well-being (3).

The gut–brain axis is now well established in the scientific literature and research shows a link between functional gastrointestinal disorders and disorders of the central nervous system, such as autism or anxious-depressive behaviors (4). In reality, almost all pathologies have (directly or indirectly) a component linked to an alteration of the gut microbiome (5).

Factors That Weaken the Microbiome

Several factors can weaken our microbiome: ultra-processed foods, low fibre intake, stress, lack of sleep, physical inactivity, poor oral hygiene, repeated use of antibiotics, or excessive alcohol and sugar consumption (the list is far from exhaustive!) (6,7,8,9,10). In the UK, these issues are compounded by limited dietary habits: average fibre intake is 19 g/day compared with the recommended 30 g and many Britons often buy the same ingredients, which reduces the diversity of the gut flora (11).

How can you support your microbiota during winter?

There’s no need for complicated diets. A few simple actions are enough: increase the proportion of varied plant foods (fruits, vegetables, legumes, whole grains, nuts, and seeds) (12). Make life easier with frozen vegetables, canned beans, or berries to add to porridges and smoothies. Also consider fermented foods (plain yogurt, kefir, sauerkraut), which provide beneficial microorganisms (13). Finally, play with herbs, spices and seasonal produce to naturally vary fibre and polyphenol intake.

A balanced microbiome supports digestion, immunity, and helps regulate mood more effectively (14). Although this does not replace medical or psychological care, taking care of your gut remains a valuable pillar of mental health especially during the long winter months in the UK!

I originally wrote this article for Le Petit Journal, a French publication, which you can find here.

References:

1. Liu, H.N.; Nakamura, M.; Kawashima, H. New Role of the Serotonin as a Biomarker of Gut–Brain Interaction. Life 2024, 14, 1280. https://doi.org/10.3390/life14101280

2. Hu gaofei, Zhu Y, Ding S, Zheng L. Role of gut microbiota in the 5-hydroxytryptamine signal transduction mechanism. Metabol Transl Med. 2023;1. doi:10.54844/mtm.2023.0344

3. Szőke, et al. "Gut dysbiosis and serotonin: intestinal 5-HT as a ubiquitous membrane permeability regulator in host tissues, organs, and the brain" Reviews in the Neurosciences, vol. 31, no. 4, 2020, pp. 415-425. https://doi.org/10.1515/revneuro-2019-0095

4. Minuti, A., et al. (2022). The complex relationship between gut microbiota dysregulation and mood disorders: A narrative review. Current Research in Neurobiology, 3, 100044.

https://doi.org/10.1016/j.crneur.2022.100044

5. Han W, et al (2022). Reviewing the role of gut microbiota in the pathogenesis of depression and exploring new therapeutic options. Front Neurosci. Dec 8;16:1029495. doi:

10.3389/fnins.2022.1029495. PMID: 36570854; PMCID: PMC9772619.

6. Hart, P. D., et al. (2019). Intakes and food sources of dietary fibre in UK adults. Nutrients, 11(8), 1839. https://doi.org/10.3390/nu11081839

7. Zheng, P., et al. (2020). Current perspectives on gut microbiome dysbiosis and depression. Advances in Therapy, 37, 1321–1339.

https://doi.org/10.1007/s12325-020-01272-7

8. Zhang, L., et al. (2025). Sleep deprivation alters gut microbiome diversity and taxonomy: A systematic review and meta-analysis. Sleep Medicine Reviews, 67, 101852.

https://doi.org/10.1016/j.smrv.2023.101852

9. Palleja, A., et al. (2018). Recovery of gut microbiota after antibiotic treatment in humans. Nature Microbiology, 3, 1255–1265. https://doi.org/10.1038/s41564-018-0257-9

10. Liu, H., et al. (2022). High sugar diets alter gut microbiota composition and host metabolism. Nutrients, 14, 3241. https://doi.org/10.3390/nu14153241

11. Mathers JC. Dietary fibre and health: the story so far. Proceedings of the Nutrition Society. 2023;82(2):120-129. doi:10.1017/S0029665123002215

12. Potter K, Gayle EJ, Deb S. Effect of gut microbiome on serotonin metabolism: a personalized treatment approach. Naunyn Schmiedebergs Arch Pharmacol. 2024 May;397(5):2589-2602. doi: 10.1007/s00210-023-02762-5. Epub 2023 Nov 3. PMID: 37922012.

13. Akram N, et al (2023). Exploring the serotonin-probiotics-gut health axis: A review of current evidence and potential mechanisms. Food Sci Nutr. Dec 7;12(2):694-706. doi:

10.1002/fsn3.3826. PMID: 38370053; PMCID: PMC10867509.

14. Sultana A, et al. The Gut Connection: A Narrative Review on the In-depth Analysis of Gut Microbiota and Metabolites in Depression. Curr Rev Clin Exp Pharmacol. 2025 Jan 31. doi: 10.2174/0127724328332998250118182255. Epub ahead of print. PMID: 39901675.