We often talk about how nutrition affects weight, digestion or energy levels. But what’s often left out of the conversation is how much what you eat affects how you feel. Your mood, motivation, clarity, and mental resilience all start in the gut. Let’s break down how nutrition, especially dietary fibre and protein, plays a key role in mental wellbeing, as we explore the gut-brain axis.
Fibre: Not Just for Digestion
Dietary fibre supports far more than just regular bowel movements. It’s essential for gut microbiota diversity, regulating metabolism, and even protecting against chronic disease. Fibre helps you feel full, improves blood sugar control, and supports immune function (Rao et al., 2015; Barber et al., 2020).
There are two types of fibre, soluble and insoluble. Soluble fibre forms a gel-like substance that slows digestion and stabilises blood sugar levels. It also gets fermented by gut bacteria into short-chain fatty acids (SCFAs) like butyrate, which reduce inflammation and support brain function (Guan et al., 2021; Choe, 2025).
Insoluble fibre acts as a bulking agent. It helps prevent constipation and supports gut motility. This type of fibre contributes indirectly to mental wellbeing by improving toxin elimination, gut integrity, and blood sugar balance (New Zealand Nutrition Foundation, n.d.).
Higher fibre intake has been linked to a lower risk of type 2 diabetes (de Munter et al., 2007), heart disease, and early death (Hartley et al., 2016). It also plays a role in mood regulation, possibly through the gut-brain axis, although more research is needed (Chen et al., 2021).
SCFAs: The Gut’s Mood Messengers
When fibre is fermented in the gut, beneficial bacteria like Bifidobacteria and Lactobacillus produce SCFAs, mainly acetate, propionate, and butyrate. These compounds are absorbed into the bloodstream and impact various physiological processes.
Butyrate supports the strength of both the gut lining and the blood-brain barrier. It helps reduce inflammation by boosting anti-inflammatory molecules like interleukin-10 and blocking inflammatory pathways (Choe, 2025b). It also improves the production of tight-junction proteins (e.g., occludin, claudin), helping prevent harmful substances from entering the bloodstream (Choe, 2025c).
SCFAs influence neurotransmitter production: butyrate boosts serotonin, dopamine, and GABA, all of which are essential for mood, cognition, and stress response (Choe, 2025d).
Serotonin: The Food-Mood Link
Serotonin regulates mood, appetite, sleep, and digestion. Around 95% of it is produced in the gut. Low serotonin levels are linked to depression, anxiety, and irritability (Bamalan et al., 2023; Carhart-Harris & Nutt, 2017).
The precursor to serotonin is tryptophan, an amino acid found in protein-rich foods. It’s converted to serotonin in a two-step process that requires iron, oxygen, BH4, and vitamin B6 (Frazer & Hensler, 1999).
Inflammation increases the breakdown of tryptophan, reducing serotonin production. Antioxidants like polyphenols and vitamins can reduce this breakdown and support mood (Strasser et al., 2016).
Carbohydrates help transport tryptophan into the brain. When carbs are eaten, insulin clears other amino acids from the blood, giving tryptophan a clear path to the brain (Wurtman & Wurtman, 1988). That’s why low-carb diets can sometimes negatively impact mood.
Gut Health = Brain Health
The diversity and balance of your gut microbiota are critical for mental health. An imbalanced microbiome (dysbiosis) can disrupt serotonin production and contribute to anxiety and depression (Appleton, 2018).
Prebiotics (fibre-rich foods) and probiotics (fermented foods) feed beneficial bacteria and support serotonin production, immune regulation, and emotional stability (Mayo Clinic, 2025).
Nutrients That Boost Mental Health
- Omega-3 fatty acids (e.g., salmon, sardines): reduce brain inflammation and support neurotransmitter function (DiNicolantonio & O’Keefe, 2020).
- Tryptophan-rich foods: turkey, eggs, tofu, oats, bananas, dark chocolate (Zuraikat et al., 2021).
- Vitamin D: linked to mood regulation and reduced depression risk (Gasmi et al., 2022).
- Wholegrains: stabilise blood sugar and provide lasting energy for the brain (Mergenthaler et al., 2013).
If you’re feeling flat, foggy, or emotionally off, look at your plate. Nutrition isn’t just about physical health, it’s about mental resilience too. A fibre-rich, protein-adequate, antioxidant-packed diet can profoundly shift how you feel, think, and cope.
Eating for your brain doesn’t need to be complicated. Focus on wholefoods, eat plenty of fibre, prioritise protein, and nourish your gut. Your mood will thank you for it.
Written and researched by Anastasia Bennett, Nutrition Coach specialising in Women’s Health and Perimenopause. Learn more at www.perimenopausehealth.co.nz.
References
Appleton, J. (2018). The gut-brain axis: Influence of microbiota on mood and mental health. Integrative Medicine (Encinitas, Calif.), 17(4), 28–32. https://pmc.ncbi.nlm.nih.gov/articles/PMC6469458/
Bamalan, O. A., Moore, M. J., & Al Khalili, Y. (2023, July 30). Physiology, serotonin. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK545168/
Barber, T. M., Kabisch, S., Pfeiffer, A. F. H., & Weickert, M. O. (2020). The health benefits of dietary fibre. Nutrients, 12(10), 3209. https://doi.org/10.3390/nu12103209
Carhart-Harris, R. L., & Nutt, D. J. (2017). Serotonin and brain function: A tale of two receptors. Journal of Psychopharmacology, 31(9), 1091–1120. https://doi.org/10.1177/0269881117725915
Chen, Y., Xu, J., & Chen, Y. (2021). Regulation of neurotransmitters by the gut microbiota and effects on cognition in neurological disorders. Nutrients, 13(6), 2099. https://doi.org/10.3390/nu13062099
Choe, U. (2025). Role of dietary fiber and short-chain fatty acids in preventing neurodegenerative diseases through the gut-brain axis. Journal of Functional Foods, 129, 106870. https://doi.org/10.1016/j.jff.2025.106870
de Munter, J. S. L., Hu, F. B., Spiegelman, D., Franz, M., & van Dam, R. M. (2007). Whole grain, bran, and germ intake and risk of type 2 diabetes: A prospective cohort study and systematic review. PLOS Medicine, 4(8), e261. https://doi.org/10.1371/journal.pmed.0040261
DiNicolantonio, J. J., & O’Keefe, J. H. (2020). The importance of marine omega-3s for brain development and the prevention and treatment of behavior, mood, and other brain disorders. Nutrients, 12(8), 2333. https://doi.org/10.3390/nu12082333
Frazer, A., & Hensler, J. G. (1999). Serotonin. In G. J. Siegel, B. W. Agranoff, R. W. Albers, et al. (Eds.), Basic neurochemistry: Molecular, cellular and medical aspects (6th ed.). Lippincott-Raven. https://www.ncbi.nlm.nih.gov/books/NBK28150/
Gasmi, A., Nasreen, A., Menzel, A., Gasmi Benahmed, A., Pivina, L., Noor, S., Peana, M., Chirumbolo, S., & Bjørklund, G. (2022). Neurotransmitters regulation and food intake: The role of dietary sources in neurotransmission. Molecules (Basel, Switzerland), 28(1), 210. https://doi.org/10.3390/molecules28010210
Guan, Z. W., Yu, E. Z., & Feng, Q. (2021). Soluble dietary fiber, one of the most important nutrients for the gut microbiota. Molecules (Basel, Switzerland), 26(22), 6802. https://doi.org/10.3390/molecules26226802
Hartley, L., May, M. D., Loveman, E., Colquitt, J. L., & Rees, K. (2016). Dietary fibre for the primary prevention of cardiovascular disease. The Cochrane Database of Systematic Reviews, 2016(1), CD011472. https://doi.org/10.1002/14651858.CD011472.pub2
Joyce, S. A., Kamil, A., Fleige, L., & Gahan, C. G. M. (2019). The cholesterol-lowering effect of oats and oat beta glucan: Modes of action and potential role of bile acids and the microbiome. Frontiers in Nutrition, 6, 171. https://doi.org/10.3389/fnut.2019.00171
Mayo Clinic. (2025, April 25). Probiotics and prebiotics: What you should know. Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/probiotics/faq-20058065
Mergenthaler, P., Lindauer, U., Dienel, G. A., & Meisel, A. (2013). Sugar for the brain: The role of glucose in physiological and pathological brain function. Trends in Neurosciences, 36(10), 587–597. https://doi.org/10.1016/j.tins.2013.07.001
New Zealand Nutrition Foundation. (n.d.). Fibre. https://nutritionfoundation.org.nz/nutrition-facts/nutrients/fibre/
Rao, S. S. C., Yu, S., & Fedewa, A. (2015). Corrigendum. Alimentary Pharmacology & Therapeutics, 42(4), 490. https://doi.org/10.1111/apt.13167
Strasser, B., Gostner, J. M., & Fuchs, D. (2016). Mood, food, and cognition: Role of tryptophan and serotonin. Current Opinion in Clinical Nutrition and Metabolic Care, 19(1), 55–61. https://doi.org/10.1097/MCO.0000000000000237
Wurtman, R. J., & Wurtman, J. J. (1988). Do carbohydrates affect food intake via neurotransmitter activity? Appetite, 11(Suppl 1), 42–47. https://pubmed.ncbi.nlm.nih.gov/2903717/
Zuraikat, F. M., Wood, R. A., Barragán, R., & St-Onge, M. P. (2021). Sleep and diet: Mounting evidence of a cyclical relationship. Annual Review of Nutrition, 41, 309–332. https://doi.org/10.1146/annurev-nutr-120420-021719
