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The Link Between Diet and Behaviour

By Junior Hudson

Many thanks to ISCP affiliate Junior Hudson for sharing his article with us, which was first published in Edition Dog Magazine.

You are what you eat, goes the saying. Dietary links to health have been well established, however, dietary links to behaviour are less discussed. What effect does diet have on our dog’s behaviour and are we worsening some behavioural issues by what we put in their bowl?

The link between artificial food colourings and hyperactivity in humans has been well documented; some of these dyes (originally derived from coal tar and now petroleum) have also been found to be carcinogenic. Whilst some are banned, numerous artificial colourings and additives still find their way into human and pet diets. The term “EC permitted additives” covers a list of about 4,000 chemicals, some colourings, flavourings and preservatives have been found to have negative behavioural effects in susceptible children. (Donna McCann, 2007) It is the belief of many professionals that similar effects may be found in dogs; however, conclusive studies have not been performed. It is typically lower quality dried foods and treats which contain these ingredients, pet parents would be wise to check labelling and use products with no artificial colourings, flavourings or preservatives.

Just as certain foods and herbs can have either inflammatory or anti-inflammatory effects in the body, they can exert similar effects in the brain. There has been much discussion concerning the links between inflammatory markers in the body and psychological disorders such as depression, anxiety etc. Pro-inflammatory cytokines (cell signallers) have been found to activate enzymes which lower Serotonin in the brain and negatively affect other neurotransmitters (Andrew H. Miller, 2013). Omega 3 acids (EPA & DHA) being one of many dietary anti-inflammatories; beneficial effects for both the body and brain, down-regulating inflammation and modulating neuro-chemical activity in the brain, improving both depressive and anxiety symptoms. Anti-inflammatory foods and herbs include; vegetables (particularly leafy green), fruit, fatty fish, seeds & nuts (Chia, Almonds, Walnut), turmeric, ginger, garlic, Extra Virgin Olive oil, amongst others.

The relationship between the gut and the brain is in fact quite intrinsic, yet we rarely pay any attention to it; the term ‘gut instinct’ is not coincidental. The Vagus nerve (known as the wandering nerve) has multiple branches, running from the brain down to the lowest point of the abdomen, touching many organs along the way. This nerve acts as a communication transmitter between the body and the brain. Studies around this nerve have demonstrated how a calm and healthy gut, can be reflected in the brain; via the communicatory utilisation of GABA and other calming neurotransmitters (Bonaz, 2018). This is one major factor in the spectrum of gut and behavioural links. Everything we do to promote gut health including; feeding fresh, less processed, biologically appropriate foods, microbiome awareness and avoiding known dietary sensitivities, ultimately can influence anxiety and other negative behavioural states.

One area of debate regarding diet and behaviour is the subject of protein; do high-protein diets cause adverse behaviour? As dogs are naturally carnivorous, common sense would say no, although it is not quite so simple. Diets above 30% protein (dry matter basis) are considered to be high-protein. I personally believe ‘moderate-high’ would be a more accurate term, for diets containing between 30 and 40 per cent protein. It is difficult to see how a high-protein diet can have negative health or behavioural effects on dogs, considering their physiological design. However, today’s dogs do not necessarily live the lives of their ancestors. Less exercise, boredom and all-around more sedentary lifestyles, may mean that we need to rethink individual dog’s nutrient needs based on their utilisation. Dogs use fat primarily but also protein as an energy source, although hypothesised there has been no conclusive evidence linking high-protein and hyperactivity (true hyperactivity is rare). There are other factors though, which I am about to discuss, which signify the need for awareness when feeding higher protein diets to dogs with existing behavioural issues.

Serotonin, a neurotransmitter in the brain, is associated with improved mood and a reduction in anxiety and aggression. Tryptophan (an amino acid), which is naturally present in protein sources, is a precursor to serotonin. However, in terms of biosynthesis, it lacks priority and competes with other protein amino acids, struggling to reach the brain and subsequently unable to boost serotonin levels. Feeding a high-protein diet can result in tryptophan depletion, which may warrant tryptophan supplementation (alongside the diet) in some dogs, particularly those with behavioural issues; dominance and territorial related aggression, most specifically (Jean S. DeNapoli, 2000). The addition of carbohydrates in the diet causes an insulin increase, which clears the way for tryptophan to cross the blood-brain barrier. In aid of this, some recommend feeding a carbohydrate source separate to and post a protein-based meal. In my experience, the general inclusion of complex carbohydrates in the diet can still be of benefit, regardless of separate meal status. It is important to remember that excessive carbohydrate content is not recommended in canine or feline diets. Regarding dietary protein, we should also be mindful of how our pet’s high-protein diets are delivered; is the protein delivered in a content of above 60% moisture (raw, cooked and canned food) or is the protein concentrated as it is in high-protein dry foods. This can affect how the body handles protein, dogs would naturally have consumed high amounts of protein but this would always have been in high moisture contents. Over-processing protein will also lead to a reduction in amino acid content, signifying further depletion of tryptophan, which as discussed previously can be counter-productive for adverse behaviours.

For health and behaviour, gut health is paramount. Particularly when addressing a dog’s reactivity, anxiety or aggression related issues, the diet should be prioritised. Balancing and harmonising the body, through dietary optimisation, microbiome awareness and immune system modulation, can help bring balance and harmony to the mind.


Andrew H. Miller, M. (2013). Cytokine Targets in the Brain: Impact on Neurotransmitters and Neurocircuits.

Bonaz, B. (2018). The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis.

Donna McCann, P. e. (2007). Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial.



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