Effect of Dietary Protein Content and Tryptophan Supplementation on Dominance Aggression, Territorial Aggression, and Hyperactivity in Dogs

Jean S. DeNapoli, Nicholas H. Dodman, Louis Shuster, William M. Rand,  Kathy L. Gross, 2000


L-tryptophan is a biosynthetic precursor for the neurotransmitter serotonin. It has been hypothesized that decreased concentrations of this amino acid would lead to reduced formation of serotonin and possibly more aggressive responses to stimuli in dogs. Three groups of dogs with dominance aggression, territorial aggression, and hyperactivity respectively were fed diets differing in protein and tryptophan levels. It was found that, for dogs with dominance aggression, adding tryptophan to a high-protein diet or changing to a low-protein diet may reduce aggression. For dogs with territorial aggression, a low-protein diet with added tryptophan may be helpful in reducing aggression. The behavior of hyperactive dogs was not influenced by dietary protein content or addition of tryptophan.

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  1. I find the information about tryptophan interesting, but I find the conclusions about protein very flawed when you look at the diet in the study. The high protein diets used, compared to the low protein diets also have a very low fat content compared to the low protein diets. Therefore the study can just as well be interpreted as “low fat diets contribute to aggression”. It is ultimately an uncontrolled study.
    Anyone reading this study may also find the study on fats and aggression interesting that was conducted 7 years later: https://www.dogtraining.world/knowledge-base/aggressive-dogs-characterized-low-omega-3-polyunsaturated-fatty-acid-status/

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