The Canine Gut-Brain Axis and why nutrition helps.
The canine gut-brain axis is a complex communication network that connects the digestive system to the brain and influences most aspects of health and wellbeing.
Essentially, this axis is an intricate bi-directional system that facilitates the exchange of information between gut and brain, in dogs and humans alike[1]. That’s a dry way of saying it is a conduit for messages from brain to gut, relaying information about cognitive and emotional activity, and from gut to brain, updating on activity in the intestinal system. These interactions enable the gut to impact mood, cognition and mental health and the brain to influence intestinal activities.
The gut-brain axis is the subject of ongoing and intensive research. Whilst there is still much to learn about the pathways and carriers of messages conveying information between the two organs, we do already know that disturbances in one organ are likely to affect the proper functioning of the other. And that when communication breaks down, health will almost inevitably suffer.
As dog owners, we need to recognise the importance of the gut-brain axis and the key role it plays in the physical and mental wellbeing of our dogs. And know that a balanced diet creates the healthy gut needed to keep communications flowing.
Communication from gut to brain
The gut microbiota in dogs consists of trillions of microorganisms, mainly bacteria, living in the digestive tract. It’s quite well known that these microorganisms are crucial for digesting food, synthesising certain vitamins, and regulating the immune system. Perhaps not so well known, but equally important, is their role in producing chemicals that send signals to the brain. Those signals tell the brain that all is well – or not.
One of the routes for information to the brain is via cytokines, molecules produced by immune cells within the gut lining that are released at low, baseline levels as part of everyday communication between gut and brain. When things are amiss, such as an infection in the gut, the immune cells release more cytokines, increasing their concentration and changing the balance of signals. That change sends an urgent warning to the brain.
Cytokines don’t cross the blood-brain barrier: they activate the vagus nerve, the primary pathway in this communication, which then relays the information about various conditions in the digestive tract to the brain. This will include conditions like gut dysbiosis, irritable bowel syndrome (IBS), inflammation – and even feelings of hunger and fullness.
And then we come to the ‘second brain’! That’s another name for the enteric nervous system (ENS), a network of neurons within the gut wall. While it can work independently to keep digestion running smoothly, the ENS is also in constant communication with the central nervous system, which includes the brain. When this network senses changes in the gut (presence of food, discomfort or infection), it manages local responses like adjusting blood flow or gut motility and simultaneously informs the brain about the changes so that it can respond.
Chemical messengers, metabolites and neurotransmitters that you’ll probably have heard of in connection with human mood, including the ‘happy hormones’ serotonin and dopamine, are produced by dogs in the gut. These chemicals are vital for regulating stress responses and affect mood, behaviour and even digestion. Working together, they help control how the body reacts to stress, how calm a dog feels and how well the digestive system functions. But when their balance is disrupted, it can lead to changes in mood or behaviour as well as problems with digestion[2].
Communication from brain to gut
Most canine research to date has focused on gut‑to‑brain signalling, since changes in gut bacteria and metabolites are easier to measure than brain‑to‑gut pathways. Research may be less extensive, yet we know that signals from the canine brain to the gut also influence its function. After all, it is described as ‘bi-directional’.
The brain sends signals to the gut for a variety of reasons: to keep digestion steady during everyday life and to adapt gut activity to suit the dog’s situation. For example, if it is resting (parasympathetic dominance: “rest and digest”), gut motility is steady and nutrients can be absorbed; when active or stressed (sympathetic dominance: “fight or flight”), the gut is essentially put on hold to divert energy to the muscles. The brain also signals the need to trigger protective changes when the dog is unwell. These signals take two main forms — electrical messages carried by nerves and chemical messages carried by hormones.
Much of this communication travels through the autonomic nervous system, i.e. the part which runs automatic processes like digestion and includes the vagus nerve and sympathetic and parasympathetic fibres (parasympathetic fibres generally promote digestion, while sympathetic fibres tend to slow it). These nerve pathways transmit rapid electrical signals directly from brain to gut, adjusting digestion ‘in real time’. That means they accelerate or decelerate the muscular contractions that move food through the intestines, increase or reduce the release of stomach acid or adjust blood flow to the gut as appropriate.
Although the enteric nervous system (that ‘second brain’) operates independently, it is also sensitive to input from the brain and will adjust its control as required when messages are received. So, if it is needed, the brain can actually override or fine‑tune ENS activity, to help coordinate digestion to its wider needs, for example during strenuous exercise or in the event of a perceived threat.
The brain also communicates with the gut using hormones released into the bloodstream. When the brain detects stress, it activates the adrenal glands to release cortisol, a stress hormone which acts directly on the gut. It too can alter motility, change the sensitivity of the gut nerves and even influence the balance of bacteria in the digestive tract. These changes are part of the body’s attempt to prepare for external threats or cope with internal strain, such as infection or inflammation.
In calmer conditions, other neurotransmitters and chemical messengers play their part. Serotonin and dopamine, for example, are produced not only in the gut but also under the brain’s direction, helping to regulate mood and digestive function together. In this way, the brain’s ongoing input through both nerve pathways and chemical signals ensures that the gut stays in tune with the dog’s emotional state, activity levels and overall health.
Studies have also linked disruptions in the canine gut‑brain axis with neurological conditions such as idiopathic epilepsy, where altered gut bacteria, immune responses and metabolites may play a role.
Supporting the gut-brain axis: What nutrition can do
Poorer diets that are high in processed, low-quality ingredients can disrupt the gut microbiome, leading to dysbiosis and potential inflammation, which can negatively affect the gut-brain axis.
A varied and balanced diet that includes fibre, beneficial bacteria and plenty of nutrient-rich foods can help maintain the healthy gut microbiome that is crucial for the gut-brain axis. The condition of the gut microbiome can directly affect, for example, the ENS and the vagus nerve. Gut health also influences production – in the gut – of key neurotransmitters and hormones like serotonin and dopamine, which are vital for mood regulation and emotional balance, and SCFAs, which can cross into the circulation to influence brain function.
(See also “The gut command centre” and “Fibre for Dogs” for ingredient examples.)
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Happy gut, happy dog
Keeping the gut happy isn’t just about digestion and stools (though goodness knows that’s important – and of course it acts as a non-invasive indicator of gut health). It’s giving your dog the best chance of being healthy and happy.
One simple takeaway: a happy gut makes for a happy dog. And a happy dog – working dog or otherwise – will get more enjoyment out of life.
References:
[1] Gernone F, Uva A, Silvestrino M, Cavalera MA, Zatelli A. Role of Gut Microbiota through Gut-Brain Axis in Epileptogenesis: A Systematic Review of Human and Veterinary Medicine. Biology (Basel). 2022 Aug 30;11(9):1290. doi: 10.3390/biology11091290. PMID: 36138769; PMCID: PMC9495720.
[2] Strandwitz P. Neurotransmitter modulation by the gut microbiota. Brain Res. 2018 Aug 15;1693(Pt B):128-133. doi: 10.1016/j.brainres.2018.03.015. PMID: 29903615; PMCID: PMC6005194.