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For those of you who are fans of diet soda, or fans of reading ingredients labels, like me,
you may have noticed a warning that says “contains phenylalanine” on every can, bottle, or jug of
diet soda you’ve ever had. Maybe you spent two seconds wondering about the dangers of this
mysterious five-syllable menace before shrugging and getting on with your refreshing beverage.
And for 99.99% of you, that’s fine. But if you happen to be one of the one in ten to fifteen
thousand people living with one rare genetic disease, that information was so important
it’s worth baffling the rest of us over. Phenylalanine is an amino acid. That is,
a basic, building-block compound the body strings together to make proteins for a variety of uses.
Phenylalanine is also a precursor in creating helpful substances like adrenaline and dopamine,
which play a variety of information-carrying roles in our body. In short, phenylalanine is
an essential ingredient in our body’s kitchen. Though as vital as phenylalanine is to the body,
it can’t be produced by the body. Instead, we get our phenylalanine fix from external sources,
mainly foods such as meat, poultry, fish, cottage cheese, lentils, peanuts, and sesame seeds. That
makes it one of the so-called essential amino acids, meaning essential to ingest in our diets.
The amino acid is also found in aspartame, an artificial sweetener used in many of the
low-calorie, super-sweet foods and beverages on the market today. That includes many diet
soda brands, sugar-free chewing gum, and so on. So, if it’s such a necessary and common
component of our diets, it seems strange why we would need to be warned of its presence. Well,
back to that point zero one percent of folks we discussed earlier. Hi, by the way. Certain
individuals simply can’t digest phenylalanine, or process it into all those helpful substances
we discussed earlier. These people suffer from a genetic disorder known as phenylketonuria,
or PKU. There are a few other similar conditions as well. People with PKU don’t correctly produce
an enzyme called phenylalanine hydroxylase, or PAH. That enzyme normally converts phenylalanine
to another amino acid, tyrosine, for further use. Without functional PAH,
high concentrations of phenylalanine can build up in the body. And phenylalanine, while necessary,
is actually neurotoxic in high concentrations. Ask any toxicologist and they’ll tell you: The dose
makes the poison. It’s the very definition of too much of a good thing. With too much
phenylalanine swimming around, PKU can result in numerous negative health effects including
intellectual disability, seizures, tremors, and ataxia if left untreated. And unfortunately,
treatment isn’t as easy as just passing on the lentils. Individuals with PKU normally have to
adhere to a low-phenylalanine diet. This is as opposite to a high-protein fad diet as you can
possibly get. It means cutting out or reducing common foods like meat, fish, eggs, cheese,
potatoes, corn, peas, and beans, and diet soda. Further, because completely eliminating protein
from the diet would cause its own set of problems for the body, individuals with PKU often have
to take poor-tasting and smelling formulas that contain other essential nutrients several times
a day. And if you’ve had this experience, you may be screaming at the screen, “Yeah,
it’s really hard!” If you are, say hi in the comments. With so many restrictions, it’s not
uncommon for individuals with PKU to struggle with maintaining such a rigid diet. Which is
why there’s a lot of motivation to develop other treatment options. Over the past few decades,
a breakthrough in PKU treatment has arisen from a surprising source: plants. In the mid 1950s,
researchers were busy working to discover the origin of lignin, a chemical that gives plants
rigidity. During their investigations, however, they found that the plants they were examining
were using an enzyme called PAL, not PAH, to break down phenylalanine into smaller compounds. So
throughout the next six decades, a hodgepodge of international researchers from various entities,
private and public, gradually built upon that fortuitous finding. They were working to see
whether PALcould do for humans what it does for plants. And it seems, for the most part,
PAL is really good at breaking down phenylalanine into harmless byproducts the body can simply flush
out. In 2018, PAL became available for daily use by injection to help manage phenylalanine levels.
Plus, it potentially allows people with PKU to transition to a more typical diet. Which means
finally enjoying a delicious, hot bowl of lentils. Every kid’s dream. But PAL can have serious side
effects for certain users. So, researchers have also been looking into other solutions. By 2019,
multiple teams of scientists had launched various types of gene-therapy experiments to treat this
disease, using mouse models of PKU. That’s right. A mouse who also can’t drink diet soda. In one
experiment, these brave, furry participants received injections of genetically edited,
PAH-producing viruses into their livers to help produce the enzyme. Instead of making the mice
sick, these so-called viral vectors would read out the gene for PAH. And, the results were promising:
the mice were able to sustain suitable phenylalanine blood levels for a period of
17 weeks. But, if you’ve ever read Steinbeck, you’ll know there’s a big difference between
Mice and Men. So, more research is underway to determine the safety and efficacy of these
kinds of therapies in humans. Lastly, if you’re wondering if you could have PKU, and need to mind
those soda warnings, you probably already know if you have it. PKU tests have been routinely given
to newborns in many countries since around the mid-1970s. And, for individuals living with PKU,
maintaining vigilance over how much phenylalanine is ingested is still a daily challenge. Hence,
the explicit advertisement on diet soda cans. So, now you know, the next time you
see an unfamiliar warning on a product, even if it doesn’t affect you, there is a reason,
because it could potentially be life-saving to someone else. So carry on with your soda.
Disclaimers for things like phenylalanine are the soda brand’s version of open and honest discourse
with you, the consumer. If you’re looking for a product that goes beyond disclosure requirements
and offers behind the scenes intel, you’ll find it in Linode. Linode is a cloud computing
company from Akamai that powers the internet worldwide through storage space, databases,
analytics and more. But they don’t keep all of that power to themselves. Their platform’s
cloud manager source code is available online, so anyone can access it. They even take it one
step further by explaining how the code works and how you can use it in video tutorials,
written guides, and real live customer support representatives available 365 days of the year.
You can see all of Linode’s tools and services by clicking the link in the description down
below or heading to linode.com/scishow. That link gives you a $100 60-day credit on a new
Linode account. Thanks to Linode for supporting this SciShow video and thank you for watching!
[♪ OUTRO]