# Phenylketonurics/Phenylalanine in Diet Coke - What's the poop?
**URL:** https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161
**Category:** Factual Questions
**Created:** [August 14, 2001, 6:00am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161 "2001-08-14T06:00:48Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@Sultan\_Kinkari](https://boards.straightdope.com/u/Sultan_Kinkari)
#### Post date: [August 14, 2001, 6:00am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/1 "2001-08-14T06:00:48Z")
Most Diet Coke® drinkers have read the term but havn’t a clue what it means.
Some people(appx. 1 in 15,000) with the recessive disorder called PKU(Phenylketonuria) are deficient in the enzyme which is necessary for metabolizing the amino acid known as Phenylalanine. Phenylalanine is found in most foods that contain protein(meat, dairy, tofu, etc.) and also aspartame, the sweetner used in most sugar-free foods including Diet Coke®. Don’t worry, usually a person knows if they have PKU.
[Here is an info. site.](http://www.ess.sunysb.edu/tracy/whatis.html)
I was always under the impression that the phenylketonuric warning on Diet Coke® cans was essentially a “drink at your own risk” warning by innuendo that meant it just may have caused cancer in lab rats. **I was wrong.** It is essentially the same thing as the “Kosher K”, a warning to consumers that it contains aspartame.
It just sounds too good to be true: A carbonated beverage that is 100% calorie-free and perfectly safe, except for the 40mg of sodium, but my blood pressure is fine.
Is there anything else I should know, considering that I drink gallons upon gallons of Diet Coke® anually?
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### Author:  [@sewalk](https://boards.straightdope.com/u/sewalk)
#### Post date: [August 14, 2001, 6:13am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/2 "2001-08-14T06:13:21Z")
Gallons per year? I probably average a gallon a day or more and have for years. If someone has a specific, citable warning, I’d be quite interested to know, too.
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### Author:  [@MrDeath](https://boards.straightdope.com/u/MrDeath)
#### Post date: [August 14, 2001, 6:25am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/3 "2001-08-14T06:25:58Z")
Aspartame is about as safe as they get if you’re not phenylketonuric.
I mean, it’s just two amino acids (phenylalanine and aspartic acid) bonded together. How much safer can you get? [Scientific studies](http://web.mit.edu/newsoffice/tt/1998/sep16/aspartame.html) have confirmed again and again that it is safe, even in ludicrously high doses.
But that doesn’t stop the fanatics. Just type “Aspartame” into Google and click on any of the first half-dozen or so links. Here’s a particularly [interesting page](http://www.rense.com/health/sweetners.htm):
> [@](#):
>
> When the temperature of Aspartame exceeds 86 degrees F, the wood alcohol in ASPARTAME coverts to formaldehyde and then to formic acid, which in turn causes metabolic acidosis.
Whoa. First off, what happens at 86 degrees F is that the bond between the two amino acids dissociates (breaks down). That’s why you can’t use the stuff in baking, for instance; you wind up with no extra sweetness and some very expensive added amino acids. Even in hot coffee, the effective sweetness of Aspartame is often noticeably reduced; if you’re heating your cup up in the microwave, add the stuff afterwards. Second off, there is _no_ wood alcohol (methanol) in Aspartame. Even if there were, converting methanol into formaldehyde in appreciable quantities requires a [catalyst](http://koken-db.kogaku.kyoto-u.ac.jp/2000/B/ML/00BML42104.html), not just the application of a smallish amount of heat.
Note: Since aspartame _is_ made from amino acids, it is not _100%_ calorie-free; I’m guessing it goes about the same level as other proteins, 4 kCal per gramme. The ads I’ve seen for Diet Coke always claim, “Just 1 Calorie!” I think that’s per 355 mL can.
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### Author:  [@barbitu8](https://boards.straightdope.com/u/barbitu8)
#### Post date: [August 14, 2001, 12:13pm UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/4 "2001-08-14T12:13:36Z")
> [@](#):
>
> \*Originally posted by MrDeath \*
> \*\*Aspartame is about as safe as they get if you’re not phenylketonuric.
>
> I mean, it’s just two amino acids (phenylalanine and aspartic acid) bonded together. How much safer can you get? [Scientific studies](http://web.mit.edu/newsoffice/tt/1998/sep16/aspartame.html) have confirmed again and again that it is safe, even in ludicrously high doses \*\*
The link refers to a study done for four months, but gives no other details concerning the study, particularly how large a group it was. It, incidentally, refers to another study with schoolchildren, but, again, no details.
Just because it’s composed of two amino acids, doesn’t mean it’s safe. Salt, which is safe to most people, is compsed of two toxins. Anecdotal reports of headaches, diarrhea, and other minor complaints have been reported from the use of aspartame. It’s questionable if aspartame is to blame, but one or two studies of an indeterminate number of subjects does not prove anything.
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### Author:  [@samclem](https://boards.straightdope.com/u/samclem)
#### Post date: [August 15, 2001, 12:37am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/5 "2001-08-15T00:37:36Z")
[Cicil’s answer](http://www.straightdope.com/classics/a961129.html)
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### Author:  [@MrDeath](https://boards.straightdope.com/u/MrDeath)
#### Post date: [August 15, 2001, 1:04am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/6 "2001-08-15T01:04:01Z")
You want cites, you got cites:
First, to show I’m not covering my ass, the [National Soft Drinks Association](http://www.nsda.org/softdrinks/aspartame.html) tell me I was wrong about the methanol-formaldehyde business. It turns out methanol is produced, in small amounts, during the metabolism of Aspartame. If you’re worried about it though, stay away from fruits and vegetables, which also contain methanol. Tomato juice too, which has five times the methanol level of metabolised Diet Coke. (The methanol comes from the fact that aspartame is in fact aspartic acid bonded to a _methyl ester_ of phenylalanine, which I didn’t know before.)
More cites from
[The American Diabetes Association](http://www.diabetes.org/main/community/info_news/news/aspartame.jsp);
[the FDA](http://vm.cfsan.fda.gov/~dms/fdsugar.html), who say that “more than 100 toxicological and clinical studies [the FDA] has reviewed confirm that aspartame is safe for the general population”;
[the Multiple Sclerosis Foundation](http://www.msfocus.org/aspart.htm), who have what appears to be the best information, including the following:
> [@](#):
>
> One small study (which has not been repeated) did find some worsening of depression when depressed patients took large doses of aspartame. . . . Several small reports have appeared showing that there may be a subset of migraine patients who worsen with aspartame. Other studies show no connection in patients who have claimed to have aspartame-related headaches.
Two studies published this year (abstracts [here](http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11468021&dopt=Abstract) and [here](http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11459435&dopt=Abstract)) indicating that aspartame in fact helps relieve arthritic pain (in rats), and a third ([here](http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11372003&dopt=Abstract)) indicating that aspartame might be effective in treating sickle-cell anemia. Another study on rats ([here](http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10972201&dopt=Abstract)), where the experimenters were expecting aspartame to increase their aggressiveness, found in fact that the rats’ aggressiveness decreased and their serotonin levels rose. Unfortunately, an article (Health News. 2001 Jan;7(1):10) titled “What’s the truth about the health risks of sugar substitutes such as saccharin and aspartame?” has no abstract available.
And salt is not composed of two toxins. Neither the sodium ion nor the chloride ion are toxic. Elemental sodium and chlorine are, but that’s a different business.
(And of course, seconds before I hit “submit”, I see **samclem** has a much better post than I. I’m going to post anyway, if only for the bit about arthritic pain and sickle-cell.)
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### Author:  [@barbitu8](https://boards.straightdope.com/u/barbitu8)
#### Post date: [August 15, 2001, 2:25am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/7 "2001-08-15T02:25:28Z")
> [@](#):
>
> \*Originally posted by samclem \*
> \*\*[Cicil’s answer](http://www.straightdope.com/classics/a961129.html) \*\*
Well, to quote a couple of sections:
> [@](#):
>
> All the noise may be obscuring some genuine problems. A 1993 study of the effect of aspartame on persons with a history of depression had to be halted because of the severity of the reaction. (For more on this see below.) I did find one study that found a connection between aspartame and headaches, and there are some persuasive anecdotal accounts.
And
> [@](#):
>
> In 1993 R. G. Walton et al reported that they had been compelled to halt a study of aspartame use by people with a history of depression because two participants suffered severe eye problems while the study was underway. One patient suffered a subconjunctival hemorrhage for the first time in her life while another required emergency surgery for a detached retina. The depressed patients also suffered other less severe symptoms.
There is some evidence that it’s not completely safe. In view of that, why go to extremes. Moderation in all things.
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### Author:  [@samclem](https://boards.straightdope.com/u/samclem)
#### Post date: [August 15, 2001, 3:23am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/8 "2001-08-15T03:23:00Z")
While I agree with both Cecil and **barbitu8** it would only be fair to quote the rest of the story about the two people with eye problems
> [@](#):
>
> one of the eye problems showed up while the subject was taking a placebo (an inactive substance) rather than aspartame.
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### Author:  [@barbitu8](https://boards.straightdope.com/u/barbitu8)
#### Post date: [August 15, 2001, 3:56pm UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/9 "2001-08-15T15:56:27Z")
I just want to add that practically any substance in excess can have deleterious side effects, even water (water intoxication). Your liver, if not diseased, can handle small portions of toxins, but you can overwhelm it. For example, Tylenol won’t hurt you if taken in moderation, but it can in excess, as well as many other NSAIDs.
As far as aspartame being a peptide and our digestive system breaks down all peptides and proteins into their individual amino acids, that is true, but again in moderation. If you drink diet Coke all day, the aspartic acid and phenylalanine can overwhelm our system, even if healthy.
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### Author:  [@MrDeath](https://boards.straightdope.com/u/MrDeath)
#### Post date: [August 15, 2001, 11:59pm UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/10 "2001-08-15T23:59:13Z")
Acetaminophen, the active ingredient in Tylenol, is not an NSAID; specifically, it is not anti-inflammatory (which is why it bugs me when they push it as arthritis medication, but that’s another story). Moreover, the toxic dose of acetaminophen, about 7 g, is _much_ lower than that of any NSAID on the market. [See what Cecil has to say.](http://www.straightdope.com/columns/000929.html)
A 355 mL can of Diet Coke contains 200 mg of Aspartame. If you drink Diet Coke all day (let’s say 32 cans, one every half-hour while you’re awake - equivalently, five and a half 2-litre bottles), you will ingest approximately 3.2 grammes each of aspartic acid and phenylalanine (I don’t know if one is heavier than the other). I don’t have figures in front of me, but I suspect you’d get more of these amino acids from scarfing down a 12-ounce steak. Meanwhile, ingesting that much liquid in a day is probably more harmful to me than 3 grammes of aspartic acid or phenylalanine (or 300-ish mg of methanol for that matter).
Most of the rest of the previous post is fairly accurate.
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### Author:  [@barbitu8](https://boards.straightdope.com/u/barbitu8)
#### Post date: [August 16, 2001, 12:16am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/11 "2001-08-16T00:16:47Z")
> [@](#):
>
> \*Originally posted by MrDeath \*
> **Acetaminophen, the active ingredient in Tylenol, is not an NSAID; specifically, it is not anti-inflammatory (which is why it bugs me when they push it as arthritis medication, but that’s another story). Moreover, the toxic dose of acetaminophen, about 7 g, is _much_ lower than that of any NSAID on the market. [See what Cecil has to say.](http://www.straightdope.com/columns/000929.html)**
Acetaminophen is an antalgesic, and not an NSAID as such, but even it has some anti-inflammatory action.
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### Author:  [@YWalker](https://boards.straightdope.com/u/YWalker)
#### Post date: [August 16, 2001, 12:43am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/12 "2001-08-16T00:43:58Z")
This issue was discussed about a month ago in the midst of [this thread](http://boards.straightdope.com/sdmb/showthread.php?threadid=75107). I’ve copied below my comments from that thread.
> [@](#):
>
> \*Originally posted by YWalker \*
>
> > [@](#):
> >
> > \*Originally posted by Marcus \*
> > \*\*Aspartame (NutraSweet) is not good for you. At all. Check out the [Aspartame Toxicity Information Center](http://www.holisticmed.com/aspartame/) if you’re interested. Check out a few case studies.
> >
> > I have avoided it like the plague for several years - I’d much rather go without, than consume it willingly. \*\*
>
> Me, too, on avoiding aspartame. I don’t believe everything I read about it, but I do know that it gives me headaches if I ingest more than just a little bit of it at a time.
>
> I was one of the earliers users of aspartame. I remember when it came only in the little blue packets (circa 1983), and wasn’t even in any soft drinks yet. I started following a recipe on the side of the box for a Grape Cooler — mix a little white grape juice with tonic water (which I hate, so I used diet Sprite, which was then sweetened with saccharine) and add a packet of Nutra-Sweet. It was great! Tasted like a grape soda, with about half the calories. I started consuming it on a regular basis. It was even better with lots of pretzels…
>
> I started getting headaches, which I at first attributed to school stress (my Senior design project was that semester), and then maybe needing new glasses (nope.) Finally, when I noted that all those “Diet” drinks plus pretzels were adding up to a lot of extra calories, I dropped my daily grape coolers, and the headaches went away — not to return until Diet Coke with Nutrasweet hit the market.
>
> When I finally figured out the second time that that Nutrasweet was giving me headaches, I did some research on the subject. There was a big research study out of Duke University debunking the “anecdotal headaches.” Being at a research university, I hit the library to look it up. The first thing I noticed about the study was that it was funded by the makers of aspartame. (Searle Labs? I don’t remember.) The second thing I noticed was that under the study protocol, I wouldn’t have ended up with headaches, either. Their protocol was based upon dosing folks with either aspartame or a placebo, with the amount given based upon their body weight. They were asked a short time later whether they had a headache. Statistically, the results between aspartame and placebo weren’t significant.
>
> I can drink one diet drink, and I won’t end up with a headache. I might have two today, and not notice anything. On the other hand, if I also had some diet jello pudding for dessert at lunch and dinner and then had a diet coke with dinner as well, I’d probably end up with a headache that night or the next day.
>
> The testing protocol didn’t allow for a cumulative effect, or a time lag, both of which were symptomatic of my “anecdotal” headaches. And, quite frankly, I don’t think that debunking research funded by the manufacturers should be considered definitive “proof” of anything.
>
> YMMV. I’ll agree aspartame is probably the best tasting substitute for sugar around — but I avoid it like the plague.
>
> By the way, **Diet Cheerwine** is another of the soft drinks that bucks the NutraSweet trend. (Sort of an aftertaste, but still nice and effervescent like the real thing.)
And now, back to this thread ----
> [@](#):
>
> _Originally posted by MrDeath_
> **I mean, it’s just two amino acids (phenylalanine and aspartic acid) bonded together. How much safer can you get? Scientific studies have confirmed again and again that it is safe, even in ludicrously high doses.**
If I may quibble, a scientific study cannot confirm that it is safe. It may confirm that a particular study finds no link between ingesting aspartame in specific quantities and particular health problems during the timeframe of the study, but it cannot confirm that there are not other issues that they were not studying or did not find, or that may show up with continued use. That said, since it has been used in such massive quantities for about 20 years, it probably isn’t massively toxic stuff for the general population — but I don’t use it, and I don’t feed it to my kids.
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### Author:  [@samclem](https://boards.straightdope.com/u/samclem)
#### Post date: [August 16, 2001, 1:23am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/13 "2001-08-16T01:23:18Z")
**MrDeath** About 3.6 gms of phenylalanine in a raw 12-oz. steak. YOur statement was correct.
Just as bad if you eat a lot of peanuts.
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### Author:  [@samclem](https://boards.straightdope.com/u/samclem)
#### Post date: [August 16, 2001, 2:09am UTC](https://boards.straightdope.com/t/phenylketonurics-phenylalanine-in-diet-coke-whats-the-poop/76161/14 "2001-08-16T02:09:07Z")
**YWalker** In the interest of science, could you answer the following questions.
l. You say that you used to consume aspartame in little blue packets in 1983 “on a regular basis.” How frequently would that be?
2. How frequently would your headaches be?
I don’t doubt that there COULD be some cause/effect. But you also gave up pretzels at the same time, assuming I understood your post. You can’t say _for sure_ that it wasn’t something in the pretzels(just to make an argument).
That seems to be the problem. There doesn’t seem to be a great deal of professional, controlled studies which prove anything.
You said
> [@](#):
>
> , I don’t think that debunking research funded by the manufacturers should be considered definitive “proof” of anything.
Would you care to offer studies done by non-manufacturers that offer definitive “proof” of anything. I think that most of the research is very poorly done.
Again, don’t get me wrong. I would dearly love to know the answers. But the anti-aspartame side has never come up with a study which offers reproducible results which would offen explanations for your “anecdotal” headaches.
…