Noodling on Nutrition

Is there a relationship between diet and behavior? Many people seem convinced that this is the case, and it's not hard to find some pretty bold assertions regarding how some diets will cure all woes, while others, or at least some ingredients, are to be avoided.

I did some searching, and the scientific evidence is sparse and rather frustrating.

One of the first papers I came across was this article about nutrition and hip dysplasia. I didn't buy it - the abstract told me enough. Rapid growth and weight gain can contribute to hip dysplasia. But this is more of a case for portion control and not free-feeding. This paper (fixed link) seems to reinforce that idea.

But what about specific macronutrients? Is a diet of all or mostly protein better than one that contains carbohydrates? I've read some, again, pretty bold assertions about dogs and protein/carbs, but where's the science?

I spent some time searching and kept coming back to the same handful of studies.

Impact of nutrition on canine behaviour: current status and possible mechanisms (fixed link), essentially concludes with "we need more study." It discusses the influence of protein, lipids, and carbohydrates on behavior, but doesn't really say much.

Studies on the effects of tryptophan or tyrosine on behaviour in dogs seem to be limited to one. DeNapoli et al. formulated diets with high or low protein content (approximately 310 or 190 g crude protein/kg, respectively) and with or without tryptophan supplementation (1·45 g/kg) in order to provide varying tryptophan contents and tryptophan:LNAA ratios (Table 1). Each of the four diets was fed in random order for 1 week to thirty-three privately owned dogs that displayed a high territorial aggression, dominance aggression or hyperactivity. There was no effect of dietary protein or tryptophan content on the behavioural scores within each group of problem behaviour. (emphasis added) However, when the groups of dogs were analysed as one study population a lower territorial aggression score was obtained for dogs fed the high-tryptophan diet compared with dogs fed the low-tryptophan diet, but only when fed a low-protein diet. In addition, dogs fed the high-protein diet without tryptophan supplementation showed a higher dominance aggression score compared with dogs on the other dietary treatments.

(I added the link to the citation in lieu of a footnote.)

So we have one study, with 33 dogs. A study that, if anything, showed more about tryptophan than anything else; and even that seems like something that needs more study.

I downloaded the study expecting to read more about the effect of carbohydrates. It's almost an article of faith with raw-feeders than dogs don't require them at all, and it's also widely believed that diets high in corn can have an effect on behavior. The study contained no direct information on starches (edited from "simple carbs" based on feedback) at all, instead focussing on the effects of fiber on satiety.

The degree of satiety in animals such as pigs has been shown to affect behaviour, including aggressive and stereotyped behaviour. Although likely, it is up till now unknown whether canine behaviour can be affected by degree of satiety and further research is required. Assuming that behaviours in dogs are more favourable during times of satiety than during times of hunger as observed in pigs (for example, aggression), specific dietary fibres through their potential to prolong satiety may assist in preventing unwanted canine behaviours.

So, it's possible, and this is all conjecture on my part, that a food that is too high in simple carbohydrates (such as corn) could reduce satiety and lead to an increase in aggressive or stereotyped behaviors.

But! the effect of fiber hasn't been studied on dogs yet, let alone the effects esimple carbs. And there's no evidence that replacing carbs with protein is any better. As a matter of fact, the one study of protein cited in this study indicates that too much protein without tryptophan can also lead to aggression:

In addition, dogs fed the high-protein diet without tryptophan supplementation showed a higher dominance aggression score compared with dogs on the other dietary treatments.

The one thing I learned from reading this is that the advice that most trainers receive — stay away from making advice about nutrition — is pretty sound. This paper went from zero to baffling in a single paragraph.

So what am I missing? Is there a body of peer-reviewed research (not just anecdotes or charges of conspiracy against the big, evil, pet food corporations) out there? I reviewed this paper for two reasons - it literally dropped in my lap over the holidays and I have also decided to participate in a product review/challenge of a food that receives a lot of criticsm from some, while having a loyal following with others. I'll be writing about that on Wednesday over at Dog Spelled Forward.

I'd really like to hear from you.