Alpha-casozepine is a decapeptide derived from alpha-s1 casein, a protein in cow's milk. Its effect is thought to be due to its action at the GABA receptor.  The dosing range is15-30 mg/kg/day. It is marketed in Canada and Europe as the supplement, Zylkene.   

Alpha casozepine has been shown to significantly decrease cortisol levels in anxious Beagles when compared to a placebo diet. In another study, a significant difference was shown between a group of cats treated with alpha casozepine and the control group regarding friendliness with familiar and unfamiliar people.  

Nicotinamide, the metabolically active form of niacin increases the affinity of GABA for its receptors.

L-tryptophan is a amino acid which is the precursor of serotonin, a neurotransmitter involved in fear and anxiety.  Its effect on the brain depends on the protein level in the diet.  

This diet is most appropriate for smaller dogs due to the dosing of the calming ingredients. The ratio of the calming ingredients to other nutritional ingredients doesn't rise linearly with the amount of food being fed to the dog. Meaning that the dose of the calming ingredients is relatively less in a larger dog when compared to a smaller dog. So, in the case of medium to large dogs, treatment with the CALM diet alone may not have as much of a clinically significant effect when compared to treatment in small dogs.   

This diet can be used with Reconcile and Clomicalm. It is a chicken based diet. The cat formulation has the same nutrient profile as Feline S/O.

I have not tried this diet myself, however I would advocate using it in small dogs who have anxiety. It is worth trying.