In Chapter 8 of The Highly Sensitive Dog, 2nd edition, I examine the prevailing myth that high-protein diets cause or contribute to aggression in dogs. (Spoiler alert: that's rubbish!)

A recent study in the Journal of the American Animal Hospital Association tries to sell us, once again, on the notion that high-protein diets increase aggression in dogs.

Davis G, Labadie J, Swafford B, et al. Association between protein content in dry dog food and aggression in Golden Retriever dogs. Journal of the American Animal Hospital Association, 2025; 61(4): 90-95.

“Our results support our hypothesis that dogs fed commercially available dry food with a high protein percentage (≥ 30%) have higher aggression scores compared with dogs fed a medium protein percentage …”

But the devil, as the saying goes, is in the details.

All of these crude-protein figures are on a dry-matter basis (i.e., discounting all water in the food).

For a little context, one popular commercial frozen raw diet for dogs contains 40% crude protein on a dry-matter basis.

Behavior categories

The ten behavior categories initially examined were these:

1. Stranger-directed aggression

2. Owner-directed aggression

3. Dog-directed aggression

4. Dog rivalry

5. Nonsocial fear

6. Stranger-directed fear

7. Dog-directed fear

8. Separation-related behaviors

9. Attachment and attention-seeking

10. Touch sensitivity

Each category comprised between four and ten questions, each question requiring a score from 0 (none/never) to 4 (severe/always). The dog's maximum score for that category was used for analysis.

Very few dogs had scores of 3 or 4 in any category, with the notable exception of 'Attachment and attention-seeking'. A whopping 97% of the dogs in this study scored between 2 and 4 in this category!

Ahh, Goldens. Gotta love 'em! ☺︎

So, 'Attachment and attention-seeking' was not analyzed in this study.

Separation-related behavior

Compared with medium-protein diets, low-protein diets significantly increased, and high-protein diets significantly decreased, the likelihood of separation-related behaviors in these dogs.

Low-protein diets increased the odds by an average of 43% (OR: 1.43; P = 0.044).

High-protein diets decreased the odds by an average of 35% (OR: 0.65; P = 0.001). This P value was the smallest (most significant) of all comparisons in this study, by far!

If this study is broadly applicable to all dogs, then feeding even a kibble diet that is higher in protein than average may reduce the likelihood of separation-related behaviors.

Now, that's good to know. (Not the kibble part; the protein part.)

Feeding a higher-protein diet may decrease the likelihood

of separation-related behaviors.

As for the dogs on the low-protein diets, it's worth noting that when the crude protein content of the diet is lowered, one or more of the other main dietary components — carbohydrates, fat, fiber, and ash (mainly minerals) — inevitably rises to take its place.

For example, here's the breakdown of that popular raw food I mentioned earlier (all percentages on a dry-matter basis):

* protein: 40%

* fat: 30%

* carbohydrates: 10%

* fiber: 10%

* ash: 10%

That adds up to 100%. If you were to lower its protein content, you'd do that by proportionately increasing one or more of the other components.

With kibble diets, it's typically the carbohydrates (especially starchy foods such as cereal grains or potatoes) that are increased, as they're cheap and easy calories.

If that was the case in this study, then we may be able to infer that the lower-protein diets were also higher-starch diets. (Although the ifs and maybes are starting to pile up here.)

As I discuss in Chapter 8 of The Highly Sensitive Dog, even moderate-starch diets increase behavioral reactivity in horses and ponies. The same is almost certainly true in dogs as well.

Even moderate-starch diets increase behavioral reactivity.

So, to the extent that a higher-protein diet is also a lower-starch diet, separation-related behaviors in dogs may respond well to increasing the protein content of the dog's diet a bit.

. . .

Stranger-directed fear

Compared with medium-protein diets, high-protein diets significantly decreased the likelihood of stranger-directed fear in these dogs.

High-protein diets decreased the odds by an average of 29% (OR: 0.71; P = 0.029).

One possible explanation is that feeding even a kibble diet that is higher in protein than average may create a greater sense of calm or confidence in some dogs, making stranger-directed fear less likely.

It's worth noting that there was no significant effect of dietary protein on stranger-directed aggression. This effect was specifically about fearfulness toward strange people. And here, a little more protein helped some dogs.

As I discuss in Chapter 2 of The Highly Sensitive Dog, fearfulness is a tricky thing to study in dogs because it is both innate and learned through specific life experiences. As with separation-related behaviors, it's good to know that nudging up the protein content of the diet may help some highly sensitive dogs be a bit less reactive when encountering strange people.

Nudging up the protein content may help some highly sensitive dogs

be a bit less fearful toward strangers.

We don't know whether this group of 1,618 Golden Retrievers included any highly sensitive dogs, but it's a fairly safe bet that it did, as this personality trait is found in every breed and the inclusion criteria did not select for/against any particular behaviors.

The authors did exclude dogs on daily behavior medications or supplements, so perhaps that filtered out a few highly sensitive dogs. But otherwise, there should have been at least 250 highly sensitive dogs (roughly 16%) in the study group.

As I discuss in the book, whenever we see a really wide range of values for what should be a fairly uniform group of individuals — such as we see with the 95% confidence intervals in this study — we can be fairly sure that the group represents individuals across the sensitivity spectrum, from very high to very low sensitivity.

. . .

Dog rivalry

However, dog rivalry was more likely in dogs on high-protein diets compared with those on medium-protein diets.

High-protein diets increased the odds by an average of 35% (OR: 1.35; P = 0.037).

In this study, dog rivalry was specifically defined as threatening or hostile responses to other familiar dogs in the same household.

What's going on there? I don't know, as family dynamics were not addressed in this study. (Gender, spay/neuter status, and age at spay/neuter were properly accounted for in the multivariable models, though.)

The effect was not large, although it was in the wrong direction, in terms of peace and harmony at home. Still, the authors are overstating their findings — by a wide margin! — in claiming higher aggression scores in the dogs on the high-protein diets.

It's also worth noting that, if dietary protein content is the main driver of this behavior, then we should have seen a significant decrease in dog rivalry in the dogs on the low-protein diets. Yet we did not.

The authors overstate their findings — by a wide margin!

. . .

Other behaviors

There were no significant effects of dietary protein on the following behavior categories:

* aggression directed toward strangers, the owner(s), or other dogs; each a separate category

* nonsocial fear (e.g., sudden or loud noises, unfamiliar objects or situations)

* dog-directed fear

* touch sensitivity (fearful or wary responses to potentially painful procedures such as grooming)

So, in this fairly large, single-breed, single-country study, the amount of protein in the dog's diet had little or no effect on reactive behaviors that are common in highly sensitive dogs, such as nonsocial fear and touch sensitivity.

That said, increasing the protein content of even a kibble diet – which would likely have lowered its carbohydrate content proportionately – significantly decreased the incidence of separation-related behaviors and stranger-directed fear.

And that makes me very happy! ☺

Increasing the protein content decreased separation-related behaviors and stranger-directed fear.

. . .

Click on the title to order The Highly Sensitive Dog, 2nd edn.