Dog Food and Behavior Problems:
Figuring Out What Causes Aggression in Dogs

If you’re like me, you may never have imagined that dog food and behavior problems could be related. If you google “Can dog food cause aggression?” very few articles show up that talk about food sensitivities causing aggression.

When reading about aggressive behavior, most articles you find either define the different types of aggression or list possible medications.

Other articles place the blame on the owner, implying they are causing the aggression to occur because they aren’t “alpha” enough.

On the positive side, there are many helpful articles that teach you training methods that reduce your dog’s stress and build their confidence (reduce fear) in potentially reactive situations. Educating yourself about how to reduce fear aggression in dogs or how to stop resource guarding in dogs is an important step to take if you have a dog exhibiting aggressive behaviors.

What frustrates me is the limited amount of information on the internet about the possible causes. The articles I could find discussed causes I couldn’t control: hormone changes, genetics, brain tumors…not much you can do in those situations.

My Dog’s Aggression Journey

Tico is a border collie German shepherd mix (we think). When he was around 7 months old, he began showing signs of fearful and aggressive behavior. I read the standard articles on dog aggression, trying to make sense of it.

But something about my dog Tico’s aggressive behavior didn’t make sense. His reactivity would be better on some days, horrible on others. I wracked my brain wondering what could change from one day to another that affected his behavior so much.

The trainer I worked with knew that weather changes could affect behavior. That made sense since I had experienced that when my kids were young. Phases of the moon were also possible behavior influencers.

I didn’t think about diet, until the oatmeal incident:

At the recommendation of Tico’s veterinary acupuncturist, we added oatmeal to his diet. Oatmeal was a “cooling” food, and she thought it might be beneficial.

Within days, his behavior changed from normal to on-alert, then to amped-up. He postured at people and dogs out our windows. Soon he started physically attacking my senior golden retriever Moose whenever he would enter the room. Tico had never displayed any aggressive behavior towards Moose before.

The aggression continued to get progressively worse. One night Tico ran at Moose, barking with teeth showing and snapping at Moose’s face. I started to cry; I knew we couldn’t keep both dogs if this continued – Tico was going to hurt Moose.

Feeling desperate, I wracked my brain trying to think of anything that had changed in the past week. The only thing I could come up with was the addition of oatmeal to his diet.

It made no sense, oatmeal would not cause aggression, right? But, it was all I could think of, so out of desperation I eliminated the oatmeal.

Within days the aggression began to subside, and Tico slowly returned to his normal behavior around Moose.

I searched the internet for articles discussing food as a cause of aggressive behavior and found nothing. But I knew with certainty that when Tico had eaten oatmeal, it had caused some type of chemical change in his brain that made him act aggressively.

It was the start of a long and frustrating road. My goal was to figure out what foods (and other things) were causing his brain to react more aggressively in certain situations.

This incident opened up a whole new way of thinking about reactivity for me. I started trying to educate myself on what factors can cause aggression that I might be able to control.

Why is My Dog Being Aggressive All of a Sudden?

Important Disclaimer: I am not a vet. Not even close. I’m just sharing my own personal experience and the information I have read. If you think you want to try something you read about here, talk to your vet! But first read this and many more articles to empower yourself for a good discussion in which you can ask your vet great questions about what you want to try.

Knowledge is power – never forget that!

dog being aggressive all of a sudden at passing dog

When a dog you have known for years starts showing aggressive behavior, it’s shocking and heart breaking. You know the potential of your dog to act sweet and loving. So why do they act so different in certain situations?

The first thing you want to do is take the dog to the vet to investigate any medical causes. The vet will run bloodwork and check for any signs of pain that your dog may be experiencing.

Before you go to your appointment, read through these possible causes of aggression so you can discuss them with your vet.

What Causes Aggression in Dogs?

Genetics

Genetics can play a part in aggression in multiple ways.

If your dog had an aggressive parent, they may have inherited some of their aggressive tendencies. One of my past dogs who showed increasing reactive behavior as he aged turned out to be from a mother who had THREE brothers euthanized for aggression. Not helpful to find that out after owning him for years, but it helped explain the aggressive behavior.

Another genetic factor comes from the dog’s in utero experience. Was the mother stressed? Underfed? Nutrient-deprived?

Patricia McConnell wrote a great article discussing how Fear in Dogs May be Influenced by In Utero Experience. This is a growing area of research and discussion. Preliminary knowledge is based on studies of humans, such as this study in which maternal stress during pregnancy was significantly correlated with infant cortisol reactivity after birth.

Socialization

Puppies miss a crucial socialization period when they are pulled from their litter too early. During this time, their mother and siblings teach them important lessons about playing and interacting with other dogs.

We think this is a factor in Tico’s aggression. He came to rescue as a tiny puppy, and we think he was pulled from his litter too early.

Socialization needs to continue once a dog is placed in a home. The goal is to expose the dog to many different situations and settings so they develop comfort and confidence in changing environments.

Thyroid

When a dog starts showing aggression out of the blue, the thyroid can be the culprit. Many vets do not check this, so it’s up to you to advocate for your dog and have the thyroid level tested.

I highly recommend having your vet send the dog’s blood draw to Dr. Jean Dodds and her staff at Hemopet. Hemopet does an age- and breed-specific analysis of your dog’s thyroid levels that flags levels that may be overlooked as “low end of normal” by a vet who doesn’t specialize in the thyroid’s effect on behavior.

Injury or Chronic Pain

Sometimes pain can be the cause of aggressive behavior. If your dog has an injury or is experiencing chronic pain, they may react toward other animals or humans who get too close or are unknowingly touching the painful area.

I found a heart-rending story that illustrates how pain can cause aggressive behavior. This poor dog was growling to try and keep people from touching a painful area of her body. Many dogs are unnecessarily and inhumanely euthanized because their owners fail to investigate this possibility.

Illness

Extreme medical conditions such as brain tumors can alter a dog’s behavior.

Eyesight

Don’t rule out poor eyesight as a cause of aggressive behavior. I read a story about a 5 month old dog who was barking aggressively and snapping at people who approached him. After some pretty intelligent observations and troubleshooting, the vet determined that the dog was aggressive because he had juvenile cataracts and couldn’t see approaching people well.

Nutritional Deficiency

Hormones and neurotransmitters regulate dog behavior. Changes in the availability of nutrients, amino acids, and enzymes that help form and regulate these hormones and neurotransmitters may influence your dog’s behavior.

For example, emerging research suggests that levels of tryptophan and DHA (from fish oil) may reduce aggression in some dogs because they can increase serotonin availability in the brain.

This article on the impact of nutrition on canine behavior discusses a number of publications that have studied this phenomenon.

Poor Gut Health

Studies in humans have shown that poor gut health can affect anxiety and behavior. Could similar findings be true for dogs?

A small study conducted by Purina (Impact of Diet on Anxious Behavior in Dogs) found that a certain probiotic (B. longum BL999) had impressive results on anxiety.

24 anxious labrador retrievers were split into two groups. One group was given a Purina probiotic product called Calming Care, which contains B. longum, the other a placebo.

Researchers then monitored anxiety-like behaviors, salivary cortisol, heart rate, and heart rate variability for 6 weeks.

After 6 weeks, all dogs were taken off supplements for 3 weeks, then the groups were reversed (initial placebo group received Calming Care, initial Calming Care group received placebo).

After 6 more weeks, the results were impressive:

  • 22 of 24 dogs showed a significant reduction in barking, jumping, spinning, and pacing while on Calming Care
  • 20 of 24 dogs showed reduced salivary cortisol concentrations when exposed to anxiety inducing stimuli while on Calming Care
  • 18 of 24 dogs had a decrease in heart rate, and 20 of 24 dogs had increased heart rate variability (both a sign of decreased stress)

I give Tico Calming Care as well. When I started giving it to him I did notice subtle but positive changes in his behavior. He is obviously also affected by food sensitivities, so Calming Care didn’t perform any miracles, but I think it gives him a more solid intestinal health base to build on.

Purina Calming Care

Food

Food sensitivities as a possible cause of behavior problems is a relatively new area of exploration. Preliminary studies are showing what some of us have seen firsthand in our dogs: food sensitivities can cause behavioral changes, including aggression.

Read on to discover more about this emerging discovery.

Dog Food and Behavior Problems

During the first few years of Tico’s aggression I started to wonder why his reactivity was so up and down. One day he would do a great job when seeing dogs or people on our walks, and I would of course think “Yay! Our training is working!” Then two days later we would have similar training opportunities and he would act like a raging lunatic.

It made no sense. I was doing the exact same training protocol. The dogs or people we saw, as far as I could tell, had no glaringly different behaviors that might make him respond differently.

So why was his aggression so unpredictable? I started to wonder . . . could the treats I was using, or the food I was feeding him, be changing his behavior?

confused woman wondering why is my dog being aggressive all of a sudden

Lack of Studies About Dog Food and Behavior Problems

When asked “Can dog food cause aggression?” many vets still shake their head and discount the idea. Most vets rely on scientific studies to learn about the causes of and solutions for aggressive behavior, and there is a significant lack of studies investigating possible links between dog food and behavior problems.

Studies are emerging, however, that are starting to look at isolated relations between food components and behavior:

Protein & L-tryptophan

A study published in the Journal of the American Veterinary Medical Association investigated the relationship between dog aggression and dietary protein content and/or L-tryptophan supplementation.

The science behind it is a bit of a brain drain, but here’s a simplified version:

L-tryptophan is an amino acid needed to form serotonin in the brain. Serotonin, in turn, can help reduce aggressive responses to stimuli.

Protein contains low amounts of L-tryptophan, but high amounts of a large neutral amino acid called LNAA. LNAA uses the same transport mechanism to cross the blood-brain barrier as L-Tryptophan – so you could think of them competing for the transport mechanism to get into the brain.

The hypothesis for this study was that lower protein would lessen the LNAA, allowing more L-tryptophan to get to the brain.

They also had one study group that was fed supplemental L-Tryptophan in addition to the low protein diet. This was building on results from a previous study about adding L-tryptophan to reduce aggression which showed inconclusive results for only adding L-Tryptophan to dogs’ diets. In its conclusion it recommended that, in future studies, L-Tryptophan be added while also lowering protein to see if that would improve the measurable response.

Results showed promising evidence that both low protein diets and low protein L-tryptophan-rich diets may decrease dominance aggression.

In addition, the study showed that low protein diets supplemented with L-tryptophan may be beneficial in reducing territorial aggression in dogs.

Gluten Hypersensitivity

I found a really interesting article in the Journal of Veterinary Behavior that explored the link between gluten hypersensitivity and dog aggression.

It discusses a case study in which a 7 year old dog was exhibiting worsening aggressive behavior that started at age 5. The dog showed no aggression in his first 5 years. Researchers found elevated antibodies indicating gluten hypersensitivity in the dog’s bloodwork results. and put the dog on a gluten-free hydrolyzed protein diet.

Three weeks after the diet change, the dog’s aggression had disappeared.

In the time that followed, the dog ingested carbohydrates two times. Once, he ate the cat’s food, which contained gluten. He became aggressive that same day and for 4 days after, but then returned to normal (no aggression).

In the second incident, the owner changed the dog’s diet to a commercial dog food. After 1 day the dog’s aggressive behavior returned. The owner immediately switched back to the gluten free hydrolyzed protein diet, and over the next 4 days the aggressive behavior disappeared.

Pretty mind-boggling, isn’t it? For me it was validating; I have known my dog reacted to different foods but to hear such a marked example of aggression turning “on” and “off” made me think about the possibility that I might be able to improve Tico’s reactivity even more with more diet refinements or omissions.

The one question I had was, why did they use a hydrolyzed diet? It makes it hard to discern if the behavior changed solely due to the removal of gluten, or if the easier-to-digest (hydrolyzed) protein was also involved.

I emailed the study author and will update this article when/if she responds.

Too Much Iodine in The Diet

This was another interesting find that could be a possible link between dog food and behavior problems. Feeding excessive amounts of iodine (either through the dog’s food or through kelp/seaweed supplements) can reduce thyroid function. Whether you feed a commercial diet or homemade, check the iodine content to be sure it isn’t too high.

“. . . the iodine concentration in commercial pet foods today is 3-5 times the stated minimum requirement, which causes more problems because excess iodine is associated with hypothyroidism and thyroiditis in dogs (and hyperthyroidism in cats).”

Dr. Jean Dodds, Nutrition and Thyroid Function Affect Canine Behavior and Cognition

Skin Responses to Dog Food Sensitivities

Dr. Dodds published a retroactive study describing food sensitivity and intolerances associated with diet type in golden retrievers. This paper does not discuss behavioral responses, but I included it as it has impressive photos of dog skin issues before and after the offending foods were removed from the dog’s diet.

Behavioral responses to food allergies are very hard to conceptualize as there is no easy-to-see visual change that occurs. But, if you think of them like the skin changes in this study, it helps you conceptualize the “path” that behavioral improvement will follow if it is caused by food sensitivities:

  • Changes are gradual and improve over time, just as the skin improvements in these pictures
  • Over time, the improvement you can achieve if you remove offending foods is quite impressive

If food sensitivities can cause severe skin problems such as the ones in Dr. Dodd’s pictures, it sure seems possible that they could affect body systems that in turn affect your dog’s temperament. (if your dog struggles with skin issues, learn more about how to treat dog allergies naturally to relieve your dog’s symptoms)

How Can I Test for Food Sensitivities?

NutriScan

I would highly recommend Dr. Dodd’s NutriScan test. Some vets don’t believe in the science behind this test, my own vet poo-poo’d it. But, I did my homework, and read many articles that supported it from a scientific perspective.

I did the Nutriscan with Tico and guess what one of his highest food sensitivities came back as . . . oatmeal! That was enough proof for me. I did not submit any information about foods Tico had eaten, just a saliva sample. If the measures of the test identified oatmeal as a trigger food, the people at Hemopet know what they are doing.

Trial and Error

Before I heard about the NutriScan test, I did a lot – and I mean A LOT – of trial and error food experimentation with Tico. This meant only making one change at a time and then waiting 4-7 days to see if I noticed any changes. If I thought I saw increased reactive behavior, I would note that in my log, then go off the food and keep notes on behavioral changes in the following 4-7 days.

Using trial and error to find links between dog food and behavior problems can be hard because other things can affect your dog’s behavior. If they have a run-in with another dog (i.e. they bark like a raging lunatic at a dog who surprises you coming around a corner on a walk), that will increase their cortisol levels and you will see behavior changes for hours or days afterward.

I swear phases of the moon and weather patterns can affect our dogs’ behavior too, just like many moms notice changes in their kids’ behavior from these things.

Trial and error can be tough because you sometimes can’t be sure what caused what. You always have to consider what else is changing or going on in your dog’s life.

Can Dog Food Cause Aggression?

happy dog with owner that figured out the connection between his dog food and behavior problems

There is no doubt in my mind that food sensitivities absolutely can and do cause aggression.

Studies are needed that delve further into the connection between dog food and behavior problems, so that owners like me don’t spend the dog’s lifetime trying to figure out why their dog’s behavior varies.

The studies above give me hope that perhaps in Tico’s lifetime I can find and eliminate enough triggers to help him become less fearful of and less reactive towards other dogs, people, bikes, skateboarders, pickup trucks . . . you get the gist.

If you have had luck identifying a connection between dog food and behavior problems in your dog, please share in the Comments section below so the rest of us can learn from your experiences!

Until next time-

Naturally,

Karen

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Karen Pedersen Written by:

Karen is an independent copywriter who loves dogs and everything about them. She is married to Scott, has 4 kids, and likes to take a natural and holistic approach to living and pet ownership.

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