Dogs are of the taxonomic order Carinvora but are not obligate carnivores and may be described as omnivores, indeed, being able to tolerate a diet high in carbohydrates. However, in March 2019, Dr Emma Bermingham et al of AgResearch at Massey University, New Zealand, conducted a study into dog nutrition. The researchers said: “Up until now science has looked at studies on nutrient digestion in humans, mice and rats and assumed the same to be true of dogs………………..much more needs to be done to understand the digestive system of dogs and the long-term health consequences of feeding different diets”. Dr Bermingham goes on to say: “We already know dogs have no nutritional need for [added] carbohydrates in their diet, so this study looked at the role different bacteria, and its production of serotonin, play in a dog’s digestive system to help us work toward a clearer picture of what is the optimum diet for dogs” (Bermingham, 2017).
Serotonin, an amino acid, is one of the constituent molecules of proteins, involved in sleep, memory, mood, depression, aggression, pain, anxiety, temperature regulation, eating behaviour and other neurological processes. It is manufactured in the brain and the intestines the majority of which, between 80-90%, can be found in the gastrointestinal (GI) tract. It is also found in the blood platelets and the central nervous system (CNS) as a neurotransmitter – though is not classified as a hormone. It is synthesized from tryptophan (trp). Tryptophan in the body has to compete with large neutral amino acids (LNAAs) found in protein, too much of which can, therefore, be potentially detrimental to a dog’s behaviour. However, using a two pronged approach the ratio of tryptophan to LNAAs can be increased in order to enhance good mood (and potentially behavioural issues in dogs). Firstly by increasing, in the diet, food rich in tryptophan such as turkey, chicken, salmon, certain red meats, oats, beans, lentils, pineapple and others. Secondly, whilst these foods alone will not boost serotonin levels and, indeed, may upset the balance causing a shortage of serotonin, the addition of certain carbohydrates in the diet will aid its absorption. These include brown rice, whole grain, fish, eggs, wheat flour, sweet potatoes, peas, carrots, beet pulp, chia seeds and oatmeal.
Nicholas Dodman, along with Drs. Richard and Elizabeth Wurtman of the Massachusetts Institute of Technology, conducted studies in 2000, the results of which were published in the Journal of the American Veterinary Medical Association (AVMA). The objective was to “evaluate the effect of high and low protein diets with or without tryptophan supplementation on behaviour of dogs with dominance aggression, territorial aggression and hyperactivity” (Dodman et al 2000). Given that the research is now 20 years old and only 33 dogs were tested it is most certainly not conclusive. The results were that dominance and territorial aggression scores were highest in dogs that were fed unsupplemented high-protein rations. Significantly lower results were obtained by feeding a low-protein tryptophan supplemented diet rather than low–protein diets without tryptophan supplements.
The results for hyperactivity appear less conclusive. In a report by Dr Karen Becker at HealthyPets-Mercola.com, she points out that hyperactivity and/or ADHD is rare amongst canines and that often, reported cases are misunderstood and may be age or breed related (Becker, 2017). The report also points out that low-protein diets for young and growing dogs should only be given under strict medical supervision.
In conclusion, protein, a macronutrient and source of slow release energy, should ideally not exceed 25% of total diet. Nicholas Dodman et al have concluded that there is a correlation between high protein diets and fear based territorial and dominance aggression. Conversely, the behaviourist and author, William E Campbell, found, in another study, that feeding more protein and fewer carbohydrates improved learning and reduced hyperactivity.
A well balanced diet, therefore, is essential for our dogs, containing, I would suggest, primarily high quality meat based protein, including organs – heart, kidney, liver – for optimum ‘performance’ whether this be dry, wet or ‘natural’ home cooked or raw food. As a treat, oily fish and cooked eggs are an excellent source of fatty acids and protein respectively along with green vegetables, certain fruits and cereals which may help boost serotonin levels (as discussed). Dogs (and cats) will sometimes forage for grass, even berries, possibly as a form of ‘self medication’. Commercial pet food manufacturers have an obligation to domesticated animals, but alas also have an obligation to their share holders and the ‘bottom line’. Learning to read the label is important as cheap meat derivatives, water, vegetable and cereal ‘fillers’ are invariably included. It is clear the ‘jury is still out’ regarding a dog’s ideal diet!
You’ve drawn the short straw this time!