Why Moss Nutrition is no Longer Selling L-Tryptophan Supplements (at least for now) – Part III

In closing part II of this series I left you with some very compelling data from the study “Tryptophan metabolism via the kynurenine pathway in patients with the eosinophilia-myalgia syndrome” by Silver et al (1) which suggests that the eosinophilia-myalgia syndrome (EMS) crisis in the late ’80s was more than just an issue of isolated batches of contaminated L-tryptophan supplements.  In fact, it may be that EMS patients presented with major pre-existing alterations in tryptophan metabolism that created a susceptibility that made them more prone to adverse reactions to both contaminated and uncontaminated L-tryptophan supplements.  Now I would like to present selected quotes from the discussion section of that paper which offer the authors’ interpretation of a data set that flies squarely in the face of the generally accepted conclusion derived over 20 years ago that elimination of the contaminant in L-tryptophan supplements totally eliminated the risk of developing EMS in all populations when these supplements are ingested.

Before presenting these quotes, though, I would like to briefly review some relevant terminology that was discussed in parts I and II of this series.  In the quote that follows you will see the terms “kynurenine” and “quinolinic acid.”  As you may recall, tryptophan is metabolized by two different, very important pathways.  With optimal health there exists good balance between these two pathways.  However, with ill-health and the chronic inflammation that most often follows, there can be increased emphasis on the pathway that produces kynurenine and quinolinic acid.  Since quinolinic acid in excess can be very detrimental to central nervous system (CNS) health, increased metabolism of tryptophan down this “kynurenine” pathway is of great concern for many researchers who focus on CNS disorders.
With this brief preface in mind, consider this first quote from the discussion section of the Silver et al (1):

“The present study demonstrates that untreated patients with EMS in the active, eosinophilic phase exhibit altered metabolism of L-tryptophan, the amino acid whose ingestion was associated with the onset of the syndrome.  These patients had significantly lower plasma LT and significantly higher plasma L-kynurenine and quinolinic acid levels than did EMS patients who were treated with corticosteroids.  Notably the increases in plasma L-kynurenine and quinolinic acid continued even though ingestion of LT had ceased weeks to months previously.  Furthermore, administration of an oral LT load revealed an accentuation of LT metabolism via the kynurenine-pathway in untreated EM patients.”

In the next quote the authors expand upon this discussion by focusing on the impact of corticosteroids on kynurenine and quinolinic acid levels:

“Corticosteroid-treated EMS patients had normal levels of L-kynurenine and quinolinic acid and responded to an LT load in manner similar to that of normal subjects.  Furthermore, treatment of EMS patients with corticosteroid was associated with normalization of plasma L-kynurenine and quinolinic acid levels.  Taken together, these data suggest that the acute phase of EMS was accompanied by the induction of IDO, resulting in the shunting of L-tryptophan via the kynurenine pathway, and that corticosteroid treatment led to normalization of LT metabolism.”

The next quote suggests that the large doses of L-tryptophan ingested by some EMS patients exacerbated the negative effect discussed above: 

“The large doses of LT consumed by patients with EMS (up to 15 gm/day) may have resulted in high levels of kynurenine-pathway metabolites in blood and extrahepatic tissues, a response accentuated by induction of IDO.”

(IDO is an abbreviation for indolamine-2,3- dioxygenase, the enzyme involved in facilitating the metabolism of L-tryptophan down the kynurenine pathway).

Therefore, with the above data in mind, it seems clear that a contaminant was not the sole cause of EMS in all afflicted patients, as has been generally accepted since the outbreak 25 years ago.

The last set of quotes I would like to present from the Silver et al (1) paper go into more detail on the effects of quinolinic acid on the CNS and how these effects are consistent with findings in EMS patients.  First, consider the following:

“Quinolinic acid excites neurons by binding to N-methyl-D-aspartate (NMDA) receptors, and in a number of experimental models, it has been shown to have direct neurotoxic effects at concentrations which, in some instances, are the same as those found in EMS patients.”

Furthermore, this impact of quinolinic acid on the CNS has been seen with other illnesses:

“Neurotoxicity has been observed in other conditions associated with chronic IDO induction and elevated concentrations of quinolinic acid.  For example, blood and CSF quinolinic acid concentrations are elevated in patients with HIV-1 infection, especially those with acquired immunodeficiency syndrome-dementia complex, whose neuropsychologic abnormalities have been shown to correlate with CSF quinolinic acid concentrations.  Furthermore, systemic administration of IFNγ is sometimes accompanied by neurologic dysfunction.  A preliminary study indicates that 60% of EMS patients report cognitive impairment.”

Next, the authors discuss the areas of the brain most affected by quinolinic acid:

“The areas of the brain believed to be the most vulnerable to the effects of quinolinic acid, the neocortex, striatum, and hippocampus, are all involved in memory and cognitive functioning, both of which may be frequently affected in EMS.” 

Thus, with all that I have presented in mind, I feel Silver et al (1) present a very strong argument that EMS causation may not be limited to contaminated L-tryptophan supplements.


In “Is the L-tryptophan metabolite quinolinic acid responsible for eosinophilic fasciitis?” by Noakes et al (2) an interesting experiment was performed.  As you will see from the following quote, the lead author had quinolinic acid administered to him to see if any aspects of EMS could be created:

“…the principal author received a series of subcutaneous injections of quinolinic acid.”

Before discussing the results of this interesting experiment, I would like to feature a quote that suggests the reason why the scientific community in the late ’80s was so quick to conclude that the EMS outbreak was due to a contaminant:

“In 1981 adulterated rapeseed (canola) oil was responsible for the toxic oil syndrome in Spain.  It shared many features in common with the EMS and eosinophilic fasciitis and was associated with altered L-tryptophan metabolism with elevated levels of both L-kynurenine and quinolinic acid being recorded.  It established a mindset between these disorders and contamination and when an epidemic of EMS occurred between 1988 and 1989 attention was directed at a contaminant found in the Showa Denko product, 1,1-ethylidenebis tryptophan, an aberrant amino acid consisting of two tryptophan molecules fused together.”

Unfortunately, this mindset seemed to blind many to the reality stated in the following quote:

“Subsequent reports however soon established a link between non-contaminated L-tryptophan and eosinophilic fasciitis.”

What were the results of the unique and unusual experiment?  The authors note:

“A total of 1200 mg of quinolinic acid was injected into the lateral thigh of the principal author over a 1-month period.  A biopsy was taken the day following the completion of the protocol.  This revealed a dense mixed infiltrate with many eosinophils and neutrophils involving the reticular dermis and septa of the panniculus.  The immunohistochemical stains for TGF-β1 showed staining of endothelial and dendritic cells.  TGF-β is known to be synthesized by dendritic cells and endothelial cells.”

Furthermore and most importantly:

“During the protocol the peripheral eosinophil count progressively rose before slowly falling towards baseline following cessation of the quinolinic acid injections.”

Of course, the argument could be made that the fact that elevated quinolinic acid is the proximate cause of many if not most of the metabolic abnormalities seen with EMS does not rule out involvement of a contaminant.  In fact, it could be suggested, quite rightly so in my opinion, that a contaminant could cause elevations in quinolinic acid.  However, as suggested above by Noakes et al (2) the fact that elevations of quinolinic acid lead to findings related to EMS also supports the contention that, contrary to established dogma, other causative agents, including uncontaminated L-tryptophan, could lead to the development of EMS.


As I mentioned, while the evidence presented both above and in parts I and II of this series are compelling, because it is epidemiologic in nature, I feel we still need a physiologic “smoking gun” of sorts to give more definitive evidence that EMS can truly be caused by uncontaminated L-tryptophan supplements.  I feel the next study I am about to review, while not absolutely conclusive, does make a strong physiologic case.

In a study which was performed on animals, “Tryptophan toxicity – time and dose response in rats” by Gross et al (3), the authors acknowledge the fact that, even though this evidence is very strong that a contaminant caused EMS, disturbances in tryptophan metabolism have been shown to cause illnesses similar to EMS:

“Even though epidemic studies indicated that a contaminant 1,1′-ethylidene-bis-tryptophan was involved in EMS, abnormalities in metabolism of Tryp have been reported in other similar clinical syndromes such as carcinoid syndrome, scleroderma or eosinophilic fasciitis.”

To provide physiologic evidence that L-tryptophan supplements could produce metabolic changes consistent with those seen with EMS patients, Gross et al (3) performed the following experiment:

“3 month old female rats were fed 3,6,12 weeks on a diet containing 20% protein diet derived from casein and supplemented with 1%, 2% or 5% Trp.  On the last week of feeding, half of the animals fed on a control diet and half of the animals fed on the Trp diet were injected with 2 injections of para-chlorophenyl alanine (p-CPA), a Trp hydroxylase inhibitor, 300 mg/kg i.p. followed by 3 injections of 100 mg/kg every alternate day.”

Why would this experiment determine whether uncontaminated L-tryptophan supplements caused EMS?  Recall from above that tryptophan is metabolized down two pathways.  The first and the most well-known leads to the production of 5-HTP, serotonin and melatonin.  The second, called the “kynurenine pathway” leads to production of a metabolite linked with the development of EMS and many other disorders, quinolinic acid.  The authors wanted to find out if excessive L-tryptophan feeding alone or excessive feeding plus para-chlorophenyl alanine (p-CPA) would cause virtually all the ingested tryptophan to be metabolized down the kynurenine pathway.  In particular, since p-CPA inhibits the enzyme tryptophan hydroxylase, which is required for tryptophan to proceed down the pathway that produces 5-HTP, serotonin and melatonin, it was expected that these rats would most certainly develop biochemical changes consistent with those seen in EMS patients.  Did one or both groups of rats develop biochemical findings consistent with those seen in EMS patients?  The authors state:

“The present study showed that treatment with excessive L-Trp or with p-CPA alone caused an increase of immunohistochemical positive TNF-α reaction in muscle and lung.”

With these findings in mind, Gross et al (3) concluded:

“It is concluded that a cumulative dose of L-Trp and the duration of exposure appears to be important in induction of pathological changes in some tissues.  Induction of the kynurenine pathway by injection of p-CPA augments some of the pathological changes and might increase mortality rate.  The present observation also confirms previous literature postulating a role of Trp and its metabolites in induction of fibrosis and inflammatory reaction.”


Of course, as we all know, no matter what the causative agent or ailment, not everyone who is exposed to the causative agent develops the ailment.  The basic precepts of functional medicine, for me, provide the best explanation for this variability.  In reality, no ailment has one and only one sole cause.  In contrast, the sometimes well known “cause” is actually a trigger, or “the straw that broke the camel’s back” so to speak, which acts with other environmental and metabolic entities, or “predisposing factors” to increase the likelihood of a negative reaction to the cause/trigger.  Could certain predisposing factors exist that explain why not everyone who ingested uncontaminated or contaminated L-tryptophan supplements developed EMS?  As you will see from the paper I am about to review, the answer is certainly yes.

In “Insulin resistance and dysregulation of tryptophan-kynurenine and kynurenine-nicotinamide adenine dinucleotide metabolic pathways” by Oxenkrug (4) the author first points out that two predisposing factors which facilitate a great many ailments in our society, inflammation and stress, can have a significant adverse impact on the kynurenine pathway:

“The first and rate-limiting step of the tryptophan (TRP)-kynurenine (KYN) pathway is regulated by enzymes inducible by pro-inflammatory factors and/or stress hormones.”

In turn, Oxenkrug (4) points out that this disturbance in the kynurenine pathway can lead to insulin resistance:

“Current review of the literature and our data presents the evidence that dysregulation of tryptophan (TRP)-kynurenine (KYN) and KYN-nicotinamide adenine dinucleotide (NAD) metabolic pathways is one of the mechanisms of insulin resistance (IR).”

Another significant predisposing factor in kynurenine pathway disturbances is vitamin B6 deficiency:

“Deficiency of P5P diverts KYN-NAD metabolism from production of NAD to the excessive formation of xanthurenic acid (XA).”

With the above in mind, Oxenkrug (4) proposes the following hypothesis:

“We propose that one of the mechanisms of IR is inflammation- and/or stress-induced upregulation of TRP-KYN metabolism in combination with P5P deficiency-induced diversion of KYN-NAD metabolism towards formation of XA and other KYN derivatives affecting insulin activity.”

As I hope you can recognize, the implications of this hypothesis are profound in terms of gaining a better understanding of why only selected individuals were afflicted with EMS after ingesting either contaminated or uncontaminated L-tryptophan supplements.  For, it suggests that the popular idea that totally healthy individuals contracted EMS only because of ingestion of contaminated or uncontaminated L-tryptophan supplements is a myth.  In reality, it is very likely that EMS patients were experiencing chronic inflammation and micronutrient deficiencies such a vitamin B6 before ingestion of the supplements which made them more susceptible to the adverse effects of the supplements.

It should also be noted that, to be precise, inflammation induces disturbances in the kynurenine pathway because of its impact on the primary enzymes that drive L-tryptophan towards the kynurenine pathway, indoleamine 2,3-dioxygenase (IDO) and TRP 2,3-dioxygenase (TDO).  Oxenkrug (4) states the following about the relationship between inflammation, IDO, and TDO:

“IDO is activated by pro-inflammatory mediators, e.g., interferon gamma (IFNG), tumor necrosis factor alpha, IL-1 beta, and lipopolysaccharide, while TDO is inducible by stress hormones, e.g., cortisol, estrogens, prolactin, and by a substrate, TRP.”

Interestingly, lipopolysaccharides are compounds produced by gut microflora that enter the bloodstream, in many instances, via increased gut permeability.  Therefore, I feel it is quite safe to hypothesize that another predisposing factor experienced by certain subpopulations of EMS patients is “leaky gut.”


With the above statements in mind, Oxenkrug (4) points out the following clinical conditions that are associated with disturbances in kynurenine metabolism:


“Clinical and experimental data suggest the increased metabolism of TRP in diabetes, resulting most likely, from the upregulation of TRP-KYN pathway.”

In addition, concerning vitamin B6:

“Low plasma concentrations of P5P have been reported in conditions associated with increased fasting glucose and glycated hemoglobin.”


“Human obesity is characterized by chronic low-grade inflammation in white adipose tissue that releases many inflammatory mediators, including KYN.”

Concerning vitamin B6:

“P5P deficiency was noted in 11% of morbid obese individuals before laparoscopic sleeve gastrectomy.  Significantly lower P5P concentrations were reported in the morbidly obese Norwegian women and men.”


“The stress-induced TDO activation that shunts TRP metabolism from the formation of serotonin towards production of KYN in depression was originally suggested in 1969.”

What role does vitamin B6 deficiency play in this scenario?  Oxenkrug (4) points out:

“One of the mechanisms of the increased incidence of IR (and diabetes) in depressed subjects might be a combination of P5P deficiency with the upregulation of TRP-KYN and dysregulation of KYN-NAD metabolic pathways.”

Cardiovascular disease

“IR, increased KYN and neopterin production, and vitamin B6 deficiency were reported in cardiovascular disease.”


“Menopause is associated with IR.  Production of IFNG, the most powerful activator of IDO, was increased in postmenopausal women.  Partial impairment in P5P-dependent kynureninase, suggesting a shift to increased production of xanthurenic acid (XA) was observed in postmenopausal women.”


“Upregulation of TRP-KYN metabolism and vitamin B6 deficiency might contribute to the development of gestational diabetes.”

With all of the above in mind, Oxenkrug (4) concludes:

“Review of the literature and our data suggests that inflammation and/or stress-induced upregulation of TRP-KYN metabolism, resulting in the excessive production of KYN, is one of the factors predisposing to IR.  Deficiency of P5P, a cofactor of the key enzyme KYN-NAD pathway, diverts the excessive amount of KYN from formation of NAD towards production of XA (and other) diabetogenic derivatives of KYN”


I realize it may appear that the running theme of this series was to discredit the commonly held assumption that a contaminant in a batch of L-tryptophan supplements caused the epidemic of EMS in the late ’80s.  In reality, I can assure you that this is not so.  For, as I have tried to demonstrate, while some of the papers presented were suggestive, none presented a strong case that the contaminant had no involvement whatsoever.  In contrast, I feel these papers made an exceedingly strong case that, contrary to the established historical dogma that we have been exposed to for most of the last 25 years, the contaminant was only one of many causative factors that contributed to the creation of so many EMS cases.  Was it the most important “straw that broke the camel’s back” for many if not most of the cases?  Unquestionably so.  However, no matter how much the contaminant contributed to the creation of EMS, I feel strongly that it cannot be denied that the contaminant, for the vast majority of the cases, was still only one of sometimes several contributing causative factors.

In addition, I feel these papers made a very strong case that EMS is not an isolated entity that occurred just for a short time when contaminated batches of L-tryptophan supplements were available to consumers.  Rather, even during the height of the outbreak plus before and after, some cases of EMS had no involvement with the contaminant.

Given that the papers I have referenced that question the “lone gunman” theory of EMS were so easy to find on Pubmed, why is it that, for the last 25 years, both the supplement industry and the clinical nutrition community have clung so voraciously to the “lone gunman” theory?  While you can probably come up with many answers to this question, the one that immediately comes to my mind is that there are powerful economic reasons for the supplement industry and the nutritional community to perpetuate the myth in the collective consciousness of the public that supplements are “idiot proof.”  What do I mean by idiot proof?  It is the myth that whether or not they are clinically effective, supplements are so benign from a risk standpoint that anyone, including those who have no knowledge of nutritional biochemistry and physiology whatsoever, can ingest supplements of any type at any quantity for even extended periods of time with absolutely no danger of adverse reactions of any type.  As you can imagine, any occurrence that even slightly dispels this myth and leads consumers to begin to believe that, because there are certain risks involved, it might be best to consult with nutritional practitioners like you before purchasing supplements, could lead to significant decreases in revenues.  Of course, as you can probably also imagine, a public admission that ingestion of L-tryptophan supplements in any dose might act as a risk factor for the development of an entity as severe as EMS independent of or in combination with the contaminant would certainly qualify as one of those “occurrences.”  Therefore, even though an occurrence such as this might result in more consumers coming to you for advice, thereby receiving more reliable, high quality information about the supplements they are purchasing, it would also undoubtedly affect the bottom line for many supplement manufacturers and retailers.

Do I have an aversion to profiting from the sales of supplements?  Definitely not.  Do I have an aversion to profiting from the sales of supplements if there is a significant risk that purchasers will receive less from the transaction in terms of safely and efficacy than I receive?  Definitely yes.  Therefore,until research proves that L-tryptophan supplements have absolutely no involvement with development of EMS in anyone or until research demonstrates a practical and cost effective way that we can determine which patients ingesting L-tryptophan supplements are likely to develop EMS, Moss Nutrition will not sell L-tryptophan supplements.

Moss Nutrition Report #256 – 04/01/2014 – PDF Version


  1. Silver RM et alTryptophan metabolism via the kynurenine pathway in patients with the eosinophilia-myalgia syndrome. Arthritis & Rheumatism. 1992;35(9):1097-105.
  2. Gross B et al. Tryptophan toxicity – time and dose response in rats. In: Huether et al, ed. Tryptophan, Serotonin, and Melatonin: Basic Aspects and Applications. New York: Plenum Publishers; 1999:507-16.
  3. Noakes R et alIs the L-tryptophan metabolite quinolinic acid responsible for eosinophilic fasciitis? Clin Exp Med. 2006;6:60-4.
  4. Oxenkrug GFInsulin resistance and dysregulation of tryptophan-kynurenine and kynurenine -nicotinamide adenine dinucleotide metabolis pathways. Mol Neurobiol. 2013;48:294-301.