Diet can affect behaviour. The extent to which it does is largely unknown at this stage. More and more research is being conducted in this area but we still know relatively little with regard to canine aggression and the influence of diet. A couple of studies have given indications, however, of an effect.
In one study two groups of aggressive dogs, displaying either household aggression or territorial aggression, were fed various degrees of protein (17%, 25% and 32%) in their diet to compare the effects. With household aggression there were no significant effects of feeding a low protein diet and, if anything, the trend was towards a decrease in aggression with a high protein diet. With territorial aggression, however, dogs on a high protein diet for 2 weeks were more aggressive towards strangers. Dogs who were fearful of strangers benefited most from the low protein diet.
Another study looked more closely at the effects of diet on canine household aggression, and compared high (30%) and low (18%) protein diets but also looked at the effects of the presence of tryptophan. Tryptophan is an essential amino acid and the precursor of serotonin, a neurotransmitter associated with feelings of well-being. In diets with high protein but without tryptophan, dogs were more aggressive around the home. The presence of tryptophan in a low protein diet decreased territorial aggression. The inclusion of essential amino acids, in particular tryptophan, in the canine diet may be a useful way of reducing household aggression.
With more knowledge and time, we may even be able to formulate diets, not just to suit stages of life but also to help with specific behaviour problems.