The Neurobehavioral Effects of Consuming Dietary Tryptophan

Monday, 9 November 2015

Glenda Lindseth, PhD, RN, FADA, FAAN
Nursing Department, University of North Dakota, Grand Forks, ND, USA
Thomas Petros, PhD
Psychology Dept, University of North Dakota, Grand Forks, ND, USA


Tryptophan, an essential amino acid, serves as a precursor to serotonin synthesis with the rate of synthesis dependent on tryptophan concentrations in the brain (Fernstrom, 2013).  Because serotonin is involved in the regulation of mood, low brain serotonin levels may contribute to increased depression.  However, tryptophan is obtained through the diet because it cannot be synthesized by the body (Soh & Walter, 2011).  Therefore, some have questioned if dietary consumption of tryptophan can affect behavior in depressed, vulnerable individuals. Sleep has also been implicated to have a relationship with tryptophan which may in turn have an effect on levels of depression. Therefore, the purpose of this study is to examine the effects of dietary tryptophan on sleep, depression, and mood in a population of depressed participants.

Based on Pender’s Health Promotion Model and using a randomized crossover study design, 36 participants with depression will be examined for differences in sleep, depression, and mood after consuming a high tryptophan diet, a low tryptophan diet and a control diet for a week each. The order of the sessions will be counterbalanced across the control and dietary treatment groups.  A two-week washout period is planned between the diets.  Study measures will include Demographics, weighed Tryptophan food Intakes, the Positive and Negative Affect Schedule,  Zung’s Self-Rating Depression Scale, the Sternberg Item Recognition Test, the Actiwatch Sleep Watch, and Serotonin and Cortisol Laboratory tests.  A repeated measures ANOVA will be used to calculate differences between sleep, depression, and mood scores resulting from the consumption of the two tryptophan diets and the control diet. Further post hoc analysis of significant results will follow. 

Benefits of this study include determining whether ingestion of functional foods, such as high tryptophan foods, may provide significant mental and physiologic benefits to vulnerable depressed individuals. The impact of these results may have a positive effect for the general population as well.