How Starch negates Proteins

The starch lines the stomach wall, having a negative effect on the pH of the hydrochloric acid in the stomach reducing the dogs ability to digest food. The only way starch can be broken down other than the very small amounts of amylase produced by the pancreas is via microbial fermentation in the gut.
This fermentation process produces large quantities of gases, which promote bloat & further reduces the ability of the dog to digest other food ingested.

Corn & Soy are made up of short-chain fatty acids, that are known to inactivate lipase, hydrochloric acid & pepsin (Brosey et al. 2000), this inevitably has a negative effect on digestion, especially of proteins and therefore the amino acids necessary for mood regulation.

Any mammal’s inherant immunity is reliant on many factors, ‘The Compliment System’ being one of the first and most important.
‘Compliments’ bind to anti-bodies, creating a catalyst to speed up an immune response and faciliate anti-bodies in targeting certain bacteria.
These ‘compliments’ are to do with proteins.
Proteins are vital for cellular repair, cellular membranes and as building blocks.
It is therefore vital that every animal obtains the correct amount of amino acids from protein in order to keep these cells and therefore the immune system healthy.

Cooking de-natures proteins. (Pond, 2003)

Here’s another scientific article about how feeding a high protein, no-grain diet, has a positive effect on behaviour: http://www.animalmedcenter.com/news-and-press/article/the-influence-of-nutrition-on-aggression