The Gut-Brain Axis: Why Your Pet’s Gut Health Shapes Their Mood

The gut-brain axis is a two-way communication system between the gastrointestinal (GI) tract and the brain. It works through neural, hormonal, immune, and microbial pathways, allowing continuous communication between the gut and the brain¹.

In simple terms:

✔ The gut can influence how your pet feels, behaves, and copes with stress.

✔ The brain can influence how well the gut functions.

Your pet’s gut microbiome - the trillions of bacteria, fungi, and other microorganisms living in the digestive system - plays a central role in mental and emotional health. When the microbiome is in balance, it helps produce key neurotransmitters like serotonin and dopamine, which regulate mood, behaviour, and stress response. Certain beneficial gut bacteria, like Lactobacillus species, can also produce GABA - a calming neurotransmitter involved in reducing anxiety. But when the gut is out of balance, so too is the brain². Supporting a healthy gut - through food, probiotics, or both - has been shown to improve emotional regulation and reduce anxiety-related behaviours in both animals and humans³. Imbalances in gut bacteria have been associated with mood disorders, poor stress resilience, aggression, and hyperactivity.

How the Gut Shapes Behaviour

Research shows strong links between gut health and behavioural outcomes in animals:

• Fecal Microbiota Transplants (FMTs) in rodents have shown that transferring gut bacteria from anxious animals to calm ones (and vice versa) can alter behaviour accordingly⁴.

• High-fat, low-carb diets in animal models like minipigs have been associated with reduced aggression and fear-related behaviours⁵.

• Probiotic supplementation has been shown to reduce anxiety, improve mood, and even modulate neurotransmitter activity in animal brains^6,7.

There’s also growing interest in the role of intestinal barrier function. For example, certain processed ingredients may increase zonulin - a protein that loosens tight junctions in the gut wall - potentially contributing to leaky gut, inflammation, and behaviour changes⁸.

These findings support what we hear every day: when pets switch to a raw, species-appropriate diet, they often become calmer, more focused, and more affectionate.

Feeding the Gut to Support the Brain

Here’s how a raw diet may support your pet’s mood and brain health:

1. Species-Appropriate Nutrition
Raw diets are naturally rich in the amino acids tryptophan and tyrosine - key building blocks for serotonin and dopamine, which support emotional regulation, focus, and mood stability. While most serotonin is produced in the gut, the brain relies on tryptophan crossing the blood–brain barrier to synthesise its own supply. Studies in dogs suggest that supplementing tryptophan may help reduce stress-related and agonistic behaviours^9,10. In contrast, high-carbohydrate diets can cause insulin spikes that may limit tryptophan’s access to the brain - potentially reducing serotonin production when it’s needed most.

2. Microbiome Support
Fresh, unprocessed foods support a more resilient microbiome, unlike ultra-processed foods (like kibble) which may disrupt microbial balance and compromise gut integrity^11,12.

3. Stable Energy, Stable Mood
Raw diets provide slow-burning energy from healthy fats and high quality animal protein, avoiding the blood sugar crashes that can come with high-carb processed foods. This helps support consistent, calm behaviour.

4. Reduced Inflammation
A healthy gut helps keep systemic inflammation low, which is increasingly recognised as a contributor to neurological and mood disorders³.

1. Bercik P, Collins SM, Verdu EF. Microbes and the gut-brain axis. Neurogastroenterol Motil. 2012 May;24(5):405-13. doi: 10.1111/j.1365-2982.2012.01906.x. PMID: 22404222.

2. Foster JA, McVey Neufeld KA. Gut–brain axis: how the microbiome influences anxiety and depression. Trends Neurosci. 2013 May;36(5):305-12. doi: 10.1016/j.tins.2013.01.005. PMID: 23384445.

3. Dinan TG, Cryan JF. The Microbiome-Gut-Brain Axis in Health and Disease. Gastroenterol Clin North Am. 2017 Mar;46(1):77-89. doi: 10.1016/j.gtc.2016.09.007. PMID: 28164855.

4. Li N, Wang Q, Wang Y, Sun A, Lin Y, Jin Y, Li X. Fecal microbiota transplantation from chronic unpredictable mild stress mice donors affects anxiety-like and depression-like behavior in recipient mice via the gut microbiota-inflammation-brain axis. Stress. 2019 Sep;22(5):592-602. doi: 10.1080/10253890.2019.1617267. PMID: 31124390.

5. Haagensen AMJ, Sørensen DB, Sandøe P, Matthews LR, Forkman B. High fat, low carbohydrate diet limits fear and aggression in Göttingen minipigs. Physiol Behav. 2014 Jul;129:64-70. doi: 10.1016/j.physbeh.2014.02.054. PMID: 24631336.

6. Borrelli L, Aceto S, Agnisola C, De Paolo S, Dipineto L, Stilling RM, Dinan TG, Cryan JF, Menna LF, Fioretti A. Probiotic modulation of the microbiota-gut-brain axis and behaviour in zebrafish. Sci Rep. 2016 Jul 15;6:30046. doi: 10.1038/srep30046. PMID: 27416816; PMCID: PMC4945902.

7. Khanna HN, Mukherjee S, Saini S, et al. Impact of probiotic supplements on behavioural and gastrointestinal symptoms in children with ASD. BMJ Paediatr Open. 2025;9(1):e003045. doi: 10.1136/bmjpo-2024-003045.

8. Fasano A. All disease begins in the (leaky) gut: role of zonulin-mediated gut permeability in the pathogenesis of some chronic inflammatory diseases. F1000Res. 2020 Jan 31;9:F1000 Faculty Rev-69. doi: 10.12688/f1000research.20510.1. PMID: 32051759; PMCID: PMC6996528.

9. Bosch G, Beerda B, Hendriks WH, van der Poel AF, Verstegen MW. Dietary tryptophan supplementation in privately owned mildly anxious dogs. Appl Anim Behav Sci. 2009 Aug;121(3-4):197-205. doi: 10.1016/j.applanim.2009.09.014.

10. Robinson E, Templeman JR, Thornton E, Croney CC, Niel L, Shoveller AK. Investigating the effects of incremental conditioning and supplemental dietary tryptophan on the voluntary activity and behaviour of mid-distance training sled dogs. PLoS One. 2020 Aug 13;15(8):e0232643. doi: 10.1371/journal.pone.0232643. PMID: 32790737; PMCID: PMC7425858..

11. Sandri M, Dal Monego S, Conte G, Sgorlon S, Stefanon B. Raw meat-based diet influences faecal microbiome and end products of fermentation in healthy dogs. BMC Vet Res. 2017 Feb 23;13(1):65. doi: 10.1186/s12917-017-0981-z. PMID: 28231824; PMCID: PMC5320848.

12. Marques TM, Cryan JF, Shanahan F, Fitzgerald GF, Ross RP, Dinan TG, Stanton C. Gut microbiota modulation and implications for host health: Dietary strategies to influence the gut–brain axis. Nutrients. 2016 Nov;8(11):E67. doi: 10.3390/nu8110676. PMID: 27801857; PMCID: PMC5133117.

13. Song SJ, Lauber C, Costello EK, Lozupone CA, Humphrey G, Berg-Lyons D, Caporaso JG, Knights D, Clemente JC, Nakielny S, Gordon JI, Fierer N, Knight R. Cohabiting family members share microbiota with one another and with their dogs. Elife. 2013 Apr 16;2:e00458. doi: 10.7554/eLife.00458. PMID: 23599893; PMCID: PMC3628085.