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Can Diet Cause Aggression in Dogs?

B-Naturals Newsletter – July 2010

Can Diet Cause Aggression in Dogs?

By Lew Olson, PhD Natural Health

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Last month we dispelled the myth about raw diets being dangerous. This month we’re going to address diets causing aggression in dogs. As always, I’m scouring the internet for valid information and research and I read a variety of responses and recommendations on this issue from the perspective of many different authors. These recommendations included reducing protein to control aggression, blaming aggression on not having enough fat in the diet, and current research trying to prove that adding tryptophan to the diet will curb aggression. There were recommendations stating more vegetables should be added to the dog’s diet and one suggestion stating you should add 5-hydroxytryptophan (5-HTP), which is a derivative of tryptophan, to a dog’s diet.

What I would like to do here is examine each of these theories, and look at how a diet may or may not change a dog’s behavior.

Many sources report reducing protein in the diet helps lessen aggression. But the best study I found doesn’t show that: http://www.ncbi.nlm.nih.gov/pubmed/8575968 :

Effect of dietary protein content on behavior in dogs.

“Results of this study suggest that a reduction in dietary protein content is not generally useful in the treatment of behavior problems in dogs, but may be appropriate in dogs with territorial aggression that is a result of fear.”

This study doesn’t state what type of food was fed, although inference from the total article leads me to believe a commercial, dry dog food was utilized. In that light, the research is limited to this one type of diet, which is a processed food that is heavily laden with starches and carbohydrates.

Newer studies are trying to prove that tryptophan (an amino acid) can help reduce aggression. The idea is that tryptophan helps with the production of serotonin, which in turn helps produce calmness. However, a glitch in the current studies is that tryptophan must be consumed with soluble fiber and the actual production of serotonin occurs during the fermentation process in the gut. Studies have been done with pigs and rats, but the study with dogs was inclusive:


“Aggressive behaviour, as well as anxiety or fearfulness in dogs, can sometimes lead to dangerous situations for the public. By changing diet composition to ensure a high enough tryptophan level and a more constant blood glucose and insulin concentration might reduce these types of behaviour. It is known that fermentable carbohydrates result in lesser fluctuations in insulin levels in the blood and that it can reduce activity in group housed pigs.

The aim of this project is to investigate which carbohydrates (in combination with tryptophan) can be added to dog’s diets without negatively affecting faecal quality (smell, volume etc.), and to investigate whether this can result in reduced undesired behaviour. “


Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs.

“For dominance aggression, behavioral scores were highest in dogs fed unsupplemented high-protein rations. For territorial aggression, [corrected] tryptophan-supplemented low-protein diets were associated with significantly lower behavioral scores than low-protein diets without tryptophan supplements. CONCLUSIONS AND CLINICAL RELEVANCE: For dogs with dominance aggression, the addition of tryptophan to high-protein diets or change to a low-protein diet may reduce aggression. For dogs with territorial aggression, tryptophan supplementation of a low-protein diet may be helpful in reducing aggression.”

While no description of the diets is revealed, my assumption is that these studies are limited to commercially processed dog food diets, which are already high in carbohydrates, use poor quality protein sources and may contain added preservatives. Their conclusion on these types of diets is that they ‘may’ reduce aggression, with no firm conclusive evidence to show that this is the case.

Further, tryptophan may not work the same in dogs as studies done with pigs, rats and humans, who have longer digestive tracts. See effects of 5-HTP on dogs (tryptophan converts to 5-HTP, and 5-HTP converts to serotonin):



“When 5-hydroxytryptophan is administered to animals, it is rapidly taken up by most tissues and is converted to serotonin wherever 5HTP decarboxylase occurs. Brain levels more than 10 times normal have been reached and maintained for several hours. At these levels laboratory animals exhibit marked central disturbance, the effects being similar to those observed after administering the hallucinogenic drug, lysergic acid diethylamide.”


“Symptoms and signs of the serotonin syndrome include confusion, agitation, diaphoresis, tachycardia, myoclonus and hyperreflexia. In addition, hypertension, coma/unresponsiveness, seizure, and death may turn out if the syndrome is not promptly recognized and treated. There are no reports of the serotonin syndrome occurring near use of 5-HTP in humans. However, it could transpire and the combination of 5-HTP with another serotonergic agent can increase the risk of it occurring. As a side document, there are 21 cases of 5-HTP toxicosis reported contained by dogs. Accidental ingestion of 5-HTP by dogs resulted in a serotonin-like syndrome. Three of the dogs died.”

What isn’t explained is that serotonin needs to be fed with soluble carbohydrates and fermented in the gut to excrete serotonin. But dogs are carnivores, and since they wouldn’t eat carbohydrates in the wild, it wouldn’t make sense that they would require serotonin, at least in this form. Why would dogs need this nutrient when their anatomy has trouble digesting large amounts of soluble fiber? What most studies have concluded is that diets with the high levels of carbohydrates creates fecal and gas problems in dogs. The volume of stool is increased significantly, and dogs struggle to ferment and digest soluble fiber in large amounts.

The most logical answer is that dogs don’t need it. What dogs do need, being carnivores to remain calm and keep blood glucose levels stable, is high quality animal protein. In a process called glyconeogenesis, amino acids and fats are converted to glucose. When dogs are fed low amounts of animal based protein, they use carbohydrates for energy. But this type of energy is not consistent and the blood sugars fluctuate, by going up and then falling. This, in turn, creates mood swings. Creating glucose from animal based proteins and fats creates a stable blood sugar level, which keeps a dog calm and focused.

Amino acids are found in proteins, and dogs, as carnivores, specifically need animal based proteins. Plant proteins lack some of the amino acids, which dogs, as carnivores specifically need. This includes l-taurine (for heart health), and l-carnitine (also for the heart and organ health). When dogs get a full complement of amino acids, it is not only calming to them, but helps support their organs, skin, coat, eyes and brain. Meat is also rich in B vitamins and minerals, including iron (which is lacking in plant based foods).

To further substantiate this, William Campbell, author of “Behavior Problems in Dogs”, reports using high quality protein has helped stop hyper-activity in dogs, and used it in his training techniques with success: http://www.webtrail.com/petbehavior/april99.html

Feeding a dog a diet high in carbohydrates, especially starches and grains, will simply create less focus and blood sugar spikes. Additionally, when carbohydrates are higher than 35% of the diet, they have the potential to ‘protein starve’ the dog, in that the dog, being a carnivore, is not getting all the amino acids necessary to sustain and maintain healthy organs, brain function, and healthy coat and skin.

Fats are also a component needed for calmness. Not only is fat satiating (helps make a dog feel full) and helps ward off dehydration, but it also contains essential fatty acids. Most importantly, DHA (docosahexaenoic acid). Research has shown dogs that display more aggressive tendencies have lower blood serum levels of DHA.


It is important to give dogs animal based sources of DHA (such as fish oils), as dogs have difficultly converting the ALA found in plant based oils. I give my dogs 180 EPA/120 DHA of fish oil per 10 to 20 lbs of body weight daily. Omega 3 fatty acids are fragile and difficult to find in food. I would also suggest using fish oil capsules, rather than bottled oil, as fish oil is fragile and easily destroyed by heat, light and air.

In conclusion, I would recommend a diet of high bioavailable animal proteins, fat and Omega 3 fatty acids to help dogs remain calm and stable. It is important to offer a variety of proteins, to make sure the dog is getting all the amino acids needed, for healthy organs, brain, nervous system function, and healthy skin, coat. If you are feeding a raw or homemade diet, it is easy enough to offer a variety of proteins. If you are feeding a commercial diet, change protein sources often and be sure to add fresh protein sources to the food, such as yogurt, eggs, meat and canned fish such as mackerel or salmon. Please note, not all aggression issues are due to diet. It is always a good idea to fully socialize any puppy or young dog through group training classes and by allowing the dog to experience numerous situations. Good food, good socialization and good training help make a calm, happy and healthy dog!

We wish all of you a very Happy and Safe 4th of July Holiday.

Please be sure to keep your dogs a safe distance from all fireworks. While we enjoy the bright colors and loud bangs, it’s an activity our dogs aren’t particularly fond of!


Dogs playing frisbee

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