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→Protein, Tryptophan and Carbohydrate
====Protein, Tryptophan and Carbohydrate====
====Protein, Tryptophan and Carbohydrate====
There are several theories about how protein, tryptophan and carbohydrates may affect behaviour. These include the following:
l-Tryptophan is large neutral amino acid (LNAA) which acts as a precursor for serotonin. l-Tryptophan is actively transported across the blood brain barrier by the L1 carrier<ref>Hawkins, R.A., O’Kane, R.L., Simpson, I.A., Vin ̃az, J.R. (2006) Structure of the Blood–Brain Barrier and Its Role in the Transport of Amino Acids. J. Nutr. 136: 218S–226S.</ref>. l-Tryptophan is therefore in competition for this carrier with other LNAAs, such as leucine, valine, methio- nine, histidine, isoleucine, tyrosine, phenylalanine, and threonine. l-Tryptophan is converted to kynurenine by the enzyme indoleamine 2,3,-dioygenase (IDO), which is activated by pro-inflammatory cytokines. Activation of Ido leads to depletion go -l-tryptophan, and therefore of serotonin, leading to signs of anxiety and depression<ref> Wichers, M.C., Maes, M. (2004) The role of indoleamine 2,3-dioxygenase (IDO) in the pathophysiology of interferon-α-induced depression. J Psychiatry Neurosci. 29(1):11-7.</ref>.
The serotonin theory of depression and anxiety led to consideration of dietary manipulation to enhance CNS availability of l-tryptophan in order to improve psychiatric symptoms. However, evident of clinical effect of l-tryptophan supplementation in humans is weak, with a Cochrane Report concluding that evidence for effect above placebo was of insufficient quality to be conclusive<ref>Shaw, K.A., Turner, J., Del Mar, C. (2008) Tryptophan and 5-Hydroxytryptophan for depressions.The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.</ref>.
There are several theories about how protein, tryptophan and carbohydrates may affect behaviour. These include the following:
*It is thought that very high protein diets could possibly result in a reduction in in the brain of levels of serotonin. Serotonin is formed from tryptophan and if amino acid levels are high competition for the carrier with tryptophan is increased. This means that lower quantities of tryptophan are able to cross the blood-brain barrier. Aggression has been linked to low serotonin levels in some cases<ref>Rosado, B., Garcia-Belenguer, S., Leon, M., et al. Blood concentrations of serotonin, cortisol, and dehydroepiandrosterone in aggressive dogs. Appl Anim Behav Sci 2010; 123:124-30</ref> and in a small percentage of dogs, diets with lower protein levels decreased territorial aggression<ref>Dodman, N.H., Reisner, I., Shuster, L., et al. Effect of dietary protein content on behaviour of dogs. J Am Vet Med Assoc 1996; 208:376-9</ref>, although other types of aggression seemed to be uninfluenced. In both dogs and cats fed a L-tryptophan supplement, lower levels of behaviours related to stress and fewer signs of anxiety were seen<ref>Da Graca Pereira, G., Fragoso, S., L-tryptophan supplementation and its effect of multi-housed cats and working dogs. Proceedings of the 2010 European Veterinary Behaviour Meeting. Hamburg, 2010, 30-35</ref><ref name="Kato">Kato, M., Miyaji, K., Ohtani, N., et al. Effects of prescription diet on dealing with stressful situations and performance of anxiety-related behaviours in privately owned anxious dogs. 2012; 7:21-6</ref>
*It is thought that very high protein diets could possibly result in a reduction in in the brain of levels of serotonin. Serotonin is formed from tryptophan and if amino acid levels are high competition for the carrier with tryptophan is increased. This means that lower quantities of tryptophan are able to cross the blood-brain barrier. Aggression has been linked to low serotonin levels in some cases<ref>Rosado, B., Garcia-Belenguer, S., Leon, M., et al. Blood concentrations of serotonin, cortisol, and dehydroepiandrosterone in aggressive dogs. Appl Anim Behav Sci 2010; 123:124-30</ref> and in a small percentage of dogs, diets with lower protein levels decreased territorial aggression<ref>Dodman, N.H., Reisner, I., Shuster, L., et al. Effect of dietary protein content on behaviour of dogs. J Am Vet Med Assoc 1996; 208:376-9</ref>, although other types of aggression seemed to be uninfluenced. In both dogs and cats fed a L-tryptophan supplement, lower levels of behaviours related to stress and fewer signs of anxiety were seen<ref>Da Graca Pereira, G., Fragoso, S., L-tryptophan supplementation and its effect of multi-housed cats and working dogs. Proceedings of the 2010 European Veterinary Behaviour Meeting. Hamburg, 2010, 30-35</ref><ref name="Kato">Kato, M., Miyaji, K., Ohtani, N., et al. Effects of prescription diet on dealing with stressful situations and performance of anxiety-related behaviours in privately owned anxious dogs. 2012; 7:21-6</ref>
*A higher carbohydrate diet is thought to be linked to tryptophan levels in the brain increasing. This as previously mentioned can be calming, which may in turn decrease the potential for aggressive behaviour. It must be noted however, that if the levels of carbohydrates are increased by reducing protein levels, the reduced protein may be the factor which causes this effect.
*A higher carbohydrate diet is thought to be linked to tryptophan levels in the brain increasing. This as previously mentioned can be calming, which may in turn decrease the potential for aggressive behaviour. It must be noted however, that if the levels of carbohydrates are increased by reducing protein levels, the reduced protein may be the factor which causes this effect.