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The importance of tryptophan in pet food was largely ignored until 2000 when DeNapoli JS, Dodman NH, Shuster L, et al. wrote a study showing how dogs fed diets with this amino acid reduced their aggression.

In our evaluation of dog food brands, we look at the composition of amino acids. This will give some insight as to how complete the diet is for a growing puppy or an adult dog.

What is Tryptophan amino acid:

Tryptophan is an essential amino acid. This means that your pet’s body cannot produce it and it must be supplied through their diet. Tryptophan has been studied for its role in helping to reduce anxiety and improve mood.

Tryptophan is a precursor to serotonin, which is a neurotransmitter that helps regulate mood, sleep, and appetite. A deficiency of tryptophan can lead to behavioral problems such as aggression and anxiety.

Is Tryptophan a solution to dog anxiety? What Research says:

Study #1:

In the Netherlands, Beerda and her colleagues from Wageningen University released a study of 138 dogs who suffered from anxiety-related behavioral problems. The control group consisted of half the dogs and were fed standard dog food and the other half were given dog food supplemented with L-tryptophan.

The study found that supplementing L-tryptophan had no effect in reducing anxiety-related behaviors in dogs.  Read the study here

Study #2:

Another 2016 study with 29 dogs was aimed at finding out if Tryptophan could improve abnormal-repetitive behavior in dogs. The study concluded that “supplementing L-tryptophan had no effects on the intensity or frequency of abnormal/repetitive behaviors”

Study #3:

A 2012 study found a small improvement in anxiety-related behaviors. It is, however, important to note that the dog food in the study was supplemented with L-tryptophan and alpha-capsazepine (a peptide found in milk protein) – not just L-tryptophan.

What does this mean to you as a pet owner?

Given that 2 of the studies claimed that tryptophan does not improve anxiety or behavioral problems in cats and dogs, and one study showed a small improvement – it is fair to say that more research needs to be done in this area.

If your dog is anxious, speak with your veterinarian about possible solutions as there are many things that can help including supplements, changes in diet, and training.

If your dog or cat is anxious, I don’t think it hurts to try it out as FDA has approved various supplements with L-tryptophan. FDA has evaluated L-tryptophan and found it to be a safe supplement for cats and dogs.

Sources of L-tryptophan:

L-tryptophan is found in animal proteins such as turkey, chicken, and beef. It is also found in some plant proteins such as soybeans and pumpkin seeds.

Benefits of Tryptophan:

The production of serotonin from tryptophan is one of the benefits associated with this amino acid. Serotonin is a neurotransmitter that helps to regulate mood, sleep, and appetite.

Another benefit of tryptophan is that it can help to improve cognitive function. A study in 2016 found that L-tryptophan supplementation improved memory and learning in aged rats.

How much tryptophan to feed dog?

AAFCo recommends that you give tryptophan to your puppy 0.20% on a dry matter basis and 0.16% to adult dogs

How much tryptophan to give cat?

AAFCO recommends that you give a min of 0.25% of tryptophan to kittens, min of 0.16% to adult cats and a max of 1.7% to older cats as shown in the table below

Do senior cats need tryptophan more?

Tryptophan is an important amino acid for senior cats. As cats age, they often suffer from cognitive decline and a decrease in serotonin levels. Supplementing with tryptophan can help to improve cognitive function and increase serotonin levels.

As you can see from the AAFCo recommendation above, senior cats need about 11 times those recommended from adult dogs and about 7 times more than the recommended amounts for kittens.

Tryptophan Deficiency Symptoms:

A deficiency of tryptophan can lead to behavioral problems such as aggression and anxiety. Supplementing with tryptophan has been shown to help reduce anxiety in some dogs.

Dog Food Brands with Tryptophan:

Tryptophan is not commonly found in dog food but there are a few brands that do include it. Here is a list of some dog food brands that include tryptophan:

  • Nature’s Variety Instinct
  • Orijen
  • Acana
  • Zignature
  • Fromm
  • Taste of the Wild
  • Blue Buffalo

1. DeNapoli JS, Dodman NH, Shuster L, et al. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. J Amer Vet Med Assoc 2000; 217:504-508.

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