Food and mood

We know that diet affects mood and behaviour in humans and animals – and it may reduce unwanted behaviour in dogs. Foods demonstrated to influence behaviour include beet pulp as a source of fibre, or salmon oil as a source of polyunsaturated fats[1]. But did you know that pumpkin seeds (a source of tryptophan) are traditionally used in China to alleviate depression?

The ‘happy hormone’

So what is tryptophan? This essential amino acid is integral to various physiological functions, including protein biosynthesis, which is fundamental for growth and tissue repair.

Tryptophan is also precursor to serotonin, the ‘happy hormone’, which supports mood regulation, emotional stability and behaviour. Research has shown that tryptophan and the “serotonergic system” can influence anxiety as well as stress-related behaviours and aggression.

Evaluating the effect of tryptophan

Vets and scientists agree that anxiety exists in dogs and that it is an important issue. One study points out that anxious states account for up to 70% of all behavioural disorders occurring in dogs[2].

The effect of tryptophan on dog mood and behaviour has been the subject of several studies. One study[3] published in the Journal of the American Veterinary Medical Association highlighted that, in combination with a low protein diet, tryptophan may positively impact on behaviour and potentially reduce stress-related aggression. Another study[4] which investigated the effect of tryptophan supplementation on anxiety- and stress-related disorders found that these behaviours decreased. A third study[5] suggested that tryptophan may decrease aggression in sled dogs without affecting performance. (Sled dogs were chosen because of their teamwork and interaction with humans and other dogs and unwanted traits that may occur such as fear, anxiety and aggression.)

Tryptophan in the diet

Because dogs are unable to synthesise tryptophan naturally, they must obtain it from their diet. The National Research Council nutrient requirements recommend that to maintain basic health, dogs be given at least 1.1 g of tryptophan for every kilo of dry food[6].

Dogs fed a varied diet including meats, fish, eggs, along with some seeds or legumes are likely to get enough tryptophan for normal physiological needs. However, tryptophan has the lowest concentration of amino acids and has to compete with the other amino acids in protein foods to get across the blood-brain barrier. So increasing protein levels effectively reduces the tryptophan ratio and as a less tryptophan gets in[7].

For most dogs, however, a healthy and balanced diet should naturally provide sufficient levels of tryptophan. Avoid the risk of over-supplementation: consult your vet before administering tryptophan supplements.

Key Natural Sources

Wholefood sources are a practical and natural way to include tryptophan in the diet. Offering foods like lean meats or kefir  are effective ways to ensure dogs receive a regular intake of this important amino acid. Complex carbohydrate sources like vegetables, fruits and legumes help to give tryptophan a better chance!

The following foods are suitable, natural sources of tryptophan which can safely be included in a dog’s diet in moderation:

  • Oats
  • Yoghurt and kefir
  • Cottage Cheese
  • Beef
  • Fish
  • Poultry
  • Sesame Seeds
  • Hemp Seeds
  • Pumpkin Seeds
  • Sunflower Seeds
  • Chickpeas
  • Buckwheat
  • Spirulina

 

Ground roast pumpkin seeds

Incorporating Tryptophan into the diet

It’s easy enough to incorporate these ingredients in the diet:

  • Meal toppers: Add lightly toasted or ground pumpkin seeds and sunflower seeds as sprinkle toppers to food.
  • Cooked meats and fish: Adding a small portion of chicken or salmon to a topping recipe.
  • Treat additions: Mixing a small amount of cottage cheese or yoghurt into homemade treats or serving a dollop with or after meals.

Tryptophan is an invaluable amino acid with multiple benefits for mood regulation, behavioural support, and cognitive health in dogs.

Natural sources provide a safe and nutritious way to incorporate tryptophan, supporting serotonin production for mood stability. In healthy animals, a balanced diet will provide the required levels.

 

References:

[1] Guido Bosch, Bonne Beerda, Anton C. Beynen, Joanne A.M. van der Borg, Antonius F.B. van der Poel, Wouter H. Hendriks, Dietary tryptophan supplementation in privately owned mildly anxious dogs, Applied Animal Behaviour Science, Volume 121, Issues 3–4, 2009, Pages 197-205, ISSN 0168-1591, https://doi.org/10.1016/j.applanim.2009.10.003.
[2] Guido Bosch, Bonne Beerda, Anton C. Beynen, Joanne A.M. van der Borg, Antonius F.B. van der Poel, Wouter H. Hendriks, Dietary tryptophan supplementation in privately owned mildly anxious dogs, Applied Animal Behaviour Science, Volume 121, Issues 3–4, 2009, Pages 197-205, ISSN 0168-1591, https://doi.org/10.1016/j.applanim.2009.10.003.
[3] DeNapoli JS, Dodman NH, Shuster L, Rand WM, Gross KL. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. J Am Vet Med Assoc. 2000;217:504–8.
[4] Pereira GG. L-Tryptophan supplementation and its effect on multi-housed cats and working dogs. Improv Vet Pract. 2010. https://www.veterinary-practice.com/article/l-tryptophan-supplementation-and-its-effect-on-multi-housed-cats-and-working-dogs.
[5] Robinson E, Templeman JR, Thornton E, Croney CC, Niel L, Shoveller AK. Investigating the effects of incremental conditioning and supplemental dietary tryptophan on the voluntary activity and behaviour of  mid-distance training sled dogs. PLoS One. 2020 Aug 13;15(8):e0232643. doi:10.1371/journal.pone.0232643. PMID: 32790737; PMCID: PMC7425858.
[6] https://pmc.ncbi.nlm.nih.gov/articles/PMC6168022/#b1-cjvr_10_294
[7] Fernstrom, J.D. Large neutral amino acids: dietary effects on brain neurochemistry and function. Amino Acids 45, 419–430 (2013). https://doi.org/10.1007/s00726-012-1330-y

 

Want to know more? These studies may be useful:

  • Templeman JR, Davenport GM, Cant JP, Osborne VR, Shoveller AK. The effect of graded concentrations of dietary tryptophan on canine behaviour in response to the approach of a familiar or unfamiliar individual. Can J Vet Res. 2018 Oct;82(4):294-305. PMID: 30363384; PMCID: PMC6168022: The Templeman study explores how varying dietary levels of tryptophan can influence canine behaviour, particularly social responses.
  • Ilana R. Reisner, J. John Mann, Michael Stanley, Yung-yu Huang, Katherine A. Houpt, Comparison of cerebrospinal fluid monoamine metabolite levels in dominant-aggressive and non-aggressive dogs, Brain Research, Volume 714, Issues 1–2, 1996, Pages 57-64, ISSN 0006-8993, https://doi.org/10.1016/0006-8993(95)01464-0: Reisner et al. provide insight into monoamine metabolite levels in aggressive versus non-aggressive dogs, examining the biochemical basis for behaviour.

 

Important Considerations:

  • Always consult your veterinarian before making any significant dietary changes, particularly where there are pre-existing health conditions or dietary restrictions.
  • If you are feeding commercial food, check the label for ingredients before giving more. Excessive intake of any foods can have adverse effects.
  • Ensure (where possible) that you use high-quality, organic products specifically formulated for pets (or better still, human grade ingredients) to avoid any potential adverse effects.
  • Introduce new foods gradually to avoid adverse effects such as gastrointestinal upset or diarrhoea.
  • I provide nutritional information purely as a helpful guide. Nutritional information on ingredients is obtained from the US Department of Agriculture’s FoodData Central site (https://fdc.nal.usda.gov/index.html) and any nutritional information provided in recipes is based on an online calculator: calories and other information will vary based on brands, ingredients and other factors.
  • Check nutrient levels and recommendations for your dog’s weight, age and activity. For example this nutritional guideline produced by FEDIAF