Thanksgiving, Turkeys, and Tryptophan

Photo credit: Tim Sackton (timsackton/Flickr)

Photo credit: Tim Sackton (timsackton/Flickr)

Turkey is the star of the most famous dinner of the year; it is also the victim of a myth that persists every holiday season. At the end of Thanksgiving dinner, there’s a good chance that someone will mention that a molecule called tryptophan is the culprit for the post-feast drowsiness. The science seems sound enough. Turkey contains tryptophan, which is a precursor for serotonin, a neurotransmitter. In turn, serotonin produces melatonin, a hormone that helps regulate sleep. This myth perpetuates, like many others, because it is based on a huge oversimplification of the truth.

On the most fundamental level, tryptophan is an essential amino acid required to make many different proteins in the body. Our bodies can’t produce tryptophan, so we have to get it from the foods we eat. Considering amino acids are used to make proteins, we get them by consuming other proteins such as meats, poultry, eggs, dairy, rice, and beans.

Chemically, tryptophan is the same whether it’s in a test tube or in our bloodstream, meaning there’s really nothing special about the tryptophan found in turkey versus other protein sources, like chicken. Turkey actually contains less tryptophan per gram than chicken, and half as much as in soybeans [1], but would anyone ever blame a tryptophan-induced food coma on a Thanksgiving chicken or tofurkey?

Tryptophan can directly cause drowsiness—if taken in pill form on an empty stomach [2]. Before tryptophan can be converted to serotonin, it must first cross the blood-brain barrier to enter the brain. This would be simple enough if tryptophan was the only amino acid capable of crossing the blood-brain barrier. However, after a meal―especially a high-protein meal like a turkey dinner―there will be many different amino acids floating around the bloodstream, many of which can also enter the brain. Despite this barrage at the gates, the brain can only take up a limited amount of amino acids. As tryptophan makes up only a small fraction of all the amino acids we consume, the other amino acids directly compete with tryptophan to cross the blood-brain barrier, ultimately decreasing tryptophan’s chances of entering the brain. Even if you stuffed yourself on nothing but tofurkey, only small amounts of tryptophan would ever enter the brain to make you sleepy.

The culprits behind the Thanksgiving dinner food coma are thus largely the high-carbohydrate dishes (and alcoholic beverages) surrounding the turkey: potatoes, yams, pies, bread, and stuffing. Eating carbohydrate-rich meals stimulates the production and release of insulin into the bloodstream [3]. Insulin then signals the uptake of amino acids into the muscles. Unlike most amino acids, tryptophan has a rather large and bulky structure that prevents it from entering muscles, so it is left behind in the bloodstream. With fewer of the other amino acids in the blood, tryptophan has less competition and is more likely to cross the blood-brain barrier, where it can be converted into serotonin and melatonin, the brain chemicals attributed to happiness and sleepiness [4].

At this point you might be thinking, “So turkey does make you sleepy! It just needs help from carbs!” Yes, but on that level, Thanksgiving dinner wouldn’t be any different from, say, a bacon and biscuits binge, or any other high-protein, high-carb meal.

And some of you might still adamantly insist, “I even eat turkey outside of Thanksgiving, and I still get super sleepy! It must be the turkey!” But remember: the sugar pill works for a reason. Never underestimate the power of the mind.

Still, don’t let any of this stop you from enjoying this holiday and stuffing your face to your heart’s content.


References Cited

  1. Foods Highest in Tryptophan. Nutrition Data.
  2. Hartmann E (1982). “Effects of L-tryptophan on sleepiness and on sleep”. Journal of Psychiatric Research 17 (2): 107–13.
  3. Wurtman RJ, Wurtman JJ, Regan MM, McDermott JM, Tsay RH, Breu JJ (2003). “Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios”. Am. J. Clin. Nutr. 77 (1): 128–32.
  4. Lyons PM, Truswell AS (1988). “Serotonin precursor influenced by type of carbohydrate meal in healthy adults”. Am. J. Clin. Nutr. 47 (3): 433–9.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Thanksgiving Tips, Tricks, and DNA

ThanksgivingTurkey

Just in time for Thanksgiving, Discover Magazine gets up close and personal with Thanksgiving genomes, and Harold McGee leads the way to a more delicious Thanksgiving dinner. Read more

5 Things About Baking

At our 2013 Science of Pie event, Christina Tosi, Zoe Nathan, and the fantastic students from the Science & Food undergraduate course taught us all about pies, baking, creativity, and the scientific process. We just can’t get enough pie science, so here are 5 fun facts related to baking and some of our favorite baking ingredients:

Baking5


Baking1


Baking2


Baking3


Baking4


Liz Roth-JohnsonAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

Read more by Liz Roth-Johnson


The Science of Cookies

How would you describe your perfect chocolate chip cookie? Thin and chewy? Ultra-crispy? Thick and cakey? Whatever your preference, knowing how to manipulate the ingredients in a basic cookie recipe is the first step toward chocolate chip cookie bliss. At last week’s “Science of Cookies” student event, graduate student Kendra Nyberg showed us how to achieve two very different cookie textures by riffing off of the classic Toll House chocolate chip cookie recipe.

ScienceofCookies

Cookies wait to be tasted (left) while Kendra explains how gluten makes cookies chewy (right)

ScienceofCookies2

Thin, chewy cookies (left) and thick, soft cookies (right)

Thin, Chewy Cookies from Smitten Kitchen
These cookies are all about moisture. A wetter cookie dough spreads more during baking, creating a much thinner cookie. Extra moisture also promotes gluten development in the cookie dough, creating a slightly denser, chewier cookie. This recipe from Smitten Kitchen maximizes moisture content by using melted butter, less flour, less egg white (which can dry out cookies), and a higher brown-to-white sugar ratio (brown sugar can help retain moisture) than the classic Toll House Recipe.

ThinChewyCookieRecipe

Thick, Soft Cookies from My Baking Addiction
Where the previous cookies craved moisture, this recipe from My Baking Addiction removes extra moisture to create thicker, less chewy cookies. Increasing the flour content and using extra cold butter creates a drier dough that spreads less easily in the oven; adding baking powder to the dough lends extra fluffing power. The reduced moisture in this dough also limits gluten formation for a slightly softer (less chewy) cookie.

ThickSoftCookieRecipe

Of course, this is barely the tip of the cookie engineering iceberg. There are so many ways to tweak a cookie recipe to achieve different textures. In addition to this brief introduction, the internet is full of great resources for cookie hacking. This particularly handy guide from Handle the Heat clearly show some of the ingredient manipulations described above. If you end up experimenting with your favorite cookie recipes, be sure to tell us about it in the comments below!


Liz Roth-JohnsonAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

Read more by Liz Roth-Johnson


WikiPearls & Dunking Science

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Harvard professor David Edwards creates a new edible food packaging, and Chef Heston Blumenthal investigates why dunking cookies in milk (or tea) makes them taste so delicious. Read more

The Science of Pie

The Science of Pie
Featuring Christina Tosi & Zoe Nathan
May 19, 2013

At the world’s first scientific bakeoff, the students of the Science & Food undergraduate course presented results from their final projects, including a live taste test of apple pies. The final projects were judged by Chefs Christina Tosi and Zoe Nathan, food critics Jonathan Gold and Evan Kleiman, and UCLA Professors Andrea Kasko, and Sally Krasne.

Chefs Christina Tosi and Zoe Nathan also shared their perspectives on inventing desserts, with an emphasis on pie. Watch the entire lecture or check out some of the shorter highlights below.

Christina Tosi on…

…creating cereal milk

“Cereal milk, fortunately for us but unfortunately for the scientific process, was very simple to make . . . But a lot of the other things that we make at Milk Bar go through a much more vigorous question asking and testing process before we actually decide whether or not its successful.”

…crack pie and re-inventing pie crust

“Crack pie is our approach to pie. It very much embodies our approach to pie. We don’t use a traditional American pie crust . . . Pie crust is an opportunity to surprise and wow and provide texture and flavor that is beyond, perhaps, you standard traditional American pie crust.”

…creativity, curiosity, and the scientific process

Whether or not we’re aware of it, the scientific process is often an integral part of cooking and baking. When Christina Tosi describes her creative process at Milk Bar, she might as well be describing the process of scientific research and discovery:

“The second that I got out of school and I was able to have my own voice, I stepped back and I looked at everything that I was taught and listened to and followed  without questioning, and I questioned it. And not in a disrespectful way, just in a ‘Well, what if? Why and what if?’ And I think that that curiosity and that forcing yourself to question every single thing in the creative process is incredibly helpful … you really just need that wandering spirit and the courage to ask ‘Why?’ And then of course the momentum and the patience to test through and be willing to fail but also be excited when you succeed.”

Zoe Nathan on…

…being a traditional baker and working with simple ingredients

“A really good baker isn’t bored of flour, and isn’t bored of sugar, and isn’t bored of salt, and isn’t bored of butter. They just know that through process they can make an entirely different thing every single day using five ingredients.”

…how to create the most amazing pie

“My second biggest pet peeve as a baker is how people bake. They forget that this is also an ingredient. Color is flavor: without it, you don’t have flavor. It just doesn’t work. Color and baking time and how your pie looks needs to be treated as another ingredient. It’s just as important as salt, sugar, flour, or anything. If you forget your color, you didn’t make the thing. . . It’s like you don’t have chocolate for your chocolate chip cookies.”

…baking and being present

“I would wish for everybody to throw away their timers and to start to engage all of their senses.  Smell! Is it done? Look at it! Is it ready? . . . The whole thing about baking is that it makes you be present.”