Tuckered Out By Turkey’s Tryptophan?

Posted by socogal42 on November 28, 2013 in Cognition, Neuroscience, NeuWrite, Thanksgiving Week, UCSD | 1 Comment

The carcass lies half eaten in the middle of the room.  Its devourers are scattered about, full stomachs groaning as they sleep off their heavy meal.  A sense of quiet calm settles around their tired forms.  Yes, it has been a successful feast, one that is taking place across a joyful nation.  I’m talking, of course, about the Thanksgiving meal where hundreds of thouands of turkeys will be consumed across America.

 

You may have heard that there’s something in turkey that contributes to that sleepy feeling some people feel after their Thanksgiving dinner.  You may also have heard that this thing is called “tryptophan.”  But is this a food fact or myth?  What can neuroscience tells us about Thanksgiving dinner?

 

What is tryptophan?

 

Tryptophan is an essential amino acid that we get from the food we eat.  It is also a precursor to the neurotransmitter serotonin.   Studies in rats have found that a diet without tryptophan leads to a significant decrease in serotonin in the brain (Biggio et. al. 1974).  Serotonin is an excitatory neurotransmitter, meaning it increases the firing rate of neurons that it affects.  Serotonin is important for mood regulation as well as sleep.

Where can we get tryptophan?

 

The human body only produces small amounts of tryptophan, so much of it has to come from food that we eat (Wurtman 1983).  We get tryptophan from products with high protein content, such as meat and dairy (Young 2007).  Interestingly, turkey may not be the only thing you eat this Thanksgiving containing tryptophan.  Spinach, seaweed, eggs and soy products have higher levels of tryptophan than turkey,  so vegetarians enjoying their tofurkey may be just as vulnerable to tryptophan-induced tiredness as their meat-eating counterparts.

 

Serotonin and tryptophan make you sleepy, right?

 

Research has suggested that serotonin plays a role in the sleep-wake cycle.  Lesions of the raphe nucleus in the brain stem, where many serotonin neurons reside, have led to disrupted sleep.  Some patients with depression complain of insomnia and disturbed sleep.  Selective serotonin re-uptake inhibitors (SSRIs) are a common class of antidepressants that keep serotonin active for longer periods of time.  When depressive patients with disturbed sleep were treated with SSRIs they reported reduced insomnia. In addition, studies have shown that blocking the function tryptophan in the brain can lead to insomnia, and this effect can be reversed by the infusion of tryptophan into the brain (Ursin 2002).

So it’s the turkey that’s giving me that food coma?

 

Not really.  Studies showing the effects of tryptophan infuse pure tryptophan directly into the brain and in much higher concentrations than normally eaten.  The tryptophan in turkey is not a pure compound and very little of it will make it into the brain, no matter how much you eat.  This is because tryptophan needs a transporter protein to get into the brain, and is competing with many other, more prevalent amino acids to get into the brain (Young 2007).  Tryptophan in its pharmaceutical form has been used as a treatment for mild depression, but only a small percentage of patients report drowsiness as a side effect (Thompson et. al. 1982).

 

Well then why am I so tired after Thanksgiving dinner?

 

It may be a condition called “postprandial somnolence” (aka food coma).  Studies have suggested that meals high in carbohydrates can lead to an increase in the hormone cholecystokinin and an increase in fatigue and sleepiness (Wells et. al. 1997) and decrease the number of other amino acids in the body, making it more likely that tryptophan will be transported into the brain (Wurtman et. al. 2003).  However, other studies have found that it may not be the composition of the meal, but the ratio of solids to liquids involved in the meal that may affect post-meal fatigue (Orr et. al. 1997).  So the turkey probably isn’t making you tired by itself, but when combined with mashed potatoes, rolls, and not enough water, it could make you want to take a nap.

So what can I do to keep myself awake?

 

Well, while Thanksgiving may be a huge event for most American families, treating it like you would any other dinner is probably your best bet to avoid falling asleep on the couch before the dishes are fully washed.  Don’t stuff yourself (delicious as the food may be), make sure to drink plenty of water, moderate your alcohol intake and keep to your regular exercise schedule.  Although, if you’re planning to hit the Black Friday sales at midnight, going to bed at 3 pm might not be the worst idea in the world.

 

References Cited

 

G. Biggio, F. Fadda, P. Fanni, A. Tagliamonte, and G. L. Gessa, Rapid depletion of serum tryptophan, brain tryptophan, serotonin and 5-hydroxyindoleacetic acid by a tryptophan-free diet. Life Sciences, 1 April 1974; 14(7): 1321-1329

 

R.J. Wurtman, Food consumption, neurotransmitter synthesis, and human behaviour. Experientia Supplementum, 1983; 44:356-36

 

S.N. Young, How to increase serotonin in the human brain without drugs. J Psychiatry Neurosci. 2007 November; 32(6): 394–399.

 

R. Ursin, Serotonin and Sleep. Sleep Medicine Review, February 2002; 6(1):55-67

 

J. Thomson, H. Rankin, G. W. Ashcroft, Celia M. Yates, J. K. McQueen and S. W. Cummings, The treatment of depression in general practice: a comparison of L-tryptophan, amitriptyline, and a combination of L-tryptophan and amitriptyline with placebo. Psychological Medicine, 1982; 12: 741-751

 

A. S. Wells, N.W Read, K Uvnas-Moberg, P Alster, Influences of Fat and Carbohydrate on Postprandial Sleepiness, Mood, and Hormones. Physiology & Behavior, May 1997; 61(5): 679-686,

 

R. J. Wurtman, J. J. Wurtman, M. M. Regan, J. M. McDermott, R. H. Tsay, and J. J. Breu

Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. American Journal of Clinical Nutrition, 2003; 77(1): 128-132

 

W. C. Orr, G. Shadid, M. J. Harnish, and S. Elsenbruch, Meal Composition and Its Effect on Postprandial Sleepiness. Physiology & Behavior, October 1997; 62(40): 709-712