Does Aspartame Cause Cancer?

Does Aspartame Cause Cancer?
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How should we parse the conflicting human data on aspartame (Nutrasweet) intake and non-Hodgkin’s lymphoma, multiple myeloma, leukemia, and pancreatic cancer?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The approval of aspartame has a controversial history. The FDA Commissioner concluded that there was “reasonable certainty that human [exposure] of aspartame…[would] not pose a risk of brain damage resulting in mental retardation, [hormonal] dysfunction, or both; and…will not cause brain tumors.” However, the FDA’s own Public Board of Inquiry withdrew their approval over cancer concerns. “Further[more], several FDA scientists advised against the approval, citing [the aspartame company’s] own brain tumor tests.” The Commissioner approved aspartame anyway, before he left the FDA, and enjoyed a “$1,000/day” consultancy position with the aspartame company’s PR firm. Then, “the FDA…actually prevented the National Toxicology Program…from doing” further cancer testing.

So, we were left with people battling over different rodent studies, some of which showed increased cancer risk, and some of which didn’t. Reminds me of the whole saccharin story, where it caused bladder cancer in rats, but not mice, leaving us with unanswerable questions like: so, are we more like a rat? Or, a mouse? We obviously had to put the aspartame question to the test in people, but the longest human safety study lasted only 18 weeks. We needed better human data.

Since the largest rat study highlighted lymphomas and leukemias, the NIH-AARP study tracked blood cancer diagnoses. And, “[h]igher levels of aspartame intake were not associated with the risk of…cancer.” It’s a massive study, but was criticized for only evaluating relatively short-term exposure; people were only studied for five years. Hey—better than 18 weeks. But, how about 18 years?

All eyes then turned to Harvard, which started following the health and diets of medical professionals since before aspartame even came on the market. “In the most comprehensive long-term [population] study to evaluate the association between aspartame intake and cancer risk in humans,” they did find an “association between [both] diet soda and total aspartame intake and [the risk] of [both non-Hodgkin’s lymphoma] and multiple myeloma in men and leukemia in both men and women.”

Okay, but, why more cancer in men than women? A similar result was found for pancreatic cancer and diet soda, but not soda in general. In fact, the only sugar tied to pancreatic cancer risk here was the “milk sugar lactose.” It was the diet soda. So, the female/male discrepancy could have just been a statistical fluke. But, they decided to dig a little deeper.

Aspartame is broken down into methanol, and the methanol is turned into formaldehyde, “a documented human carcinogen” by this enzyme here, alcohol dehydrogenase. The same enzyme that detoxifies regular alcohol is the same enzyme that converts methanol to formaldehyde.

Is it possible men just have higher levels of this enzyme than women? Yes, that’s why women get higher blood alcohol levels drinking the same amount of alcohol. If you look at liver samples from men and women, there’s significantly greater enzyme activity in the men. So, maybe that explains the increased cancer risk in men—the higher conversion rates from aspartame to formaldehyde. But how do we test it?

Well, ethanol—regular alcohol—competes with methanol for this same enzyme’s attention. In fact, regular alcohol is actually “used as an antidote for methanol poisoning.” So, men who don’t drink may have higher formaldehyde conversion rates from aspartame if this whole formaldehyde theory is correct, and indeed, consistent with this line of reasoning, it was the men that drank the least alcohol that appeared to have the greatest cancer risk from aspartame.

A third cohort study has since been published, and found no increased lymphoma risk associated with diet soda during a ten-year follow-up period. So, no risk detected in the 18-week study, the 5-year study, or the 10-year study—only in the 18-year study. What should we make of all this?

Some have called for a “re-evaluation” of the safety of aspartame. The horse is kind of out of the barn at this point, with “34,000,000 pounds” of the stuff produced annually, but that doesn’t mean we have to eat it—especially, perhaps, pregnant women and children.

Please consider volunteering to help out on the site.

Image credits: Emw via WikimediaImages and https://pixabay.com/en/aspartame-sweetener-molecule-model-884052 via pixabay. Images have been modified.

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The approval of aspartame has a controversial history. The FDA Commissioner concluded that there was “reasonable certainty that human [exposure] of aspartame…[would] not pose a risk of brain damage resulting in mental retardation, [hormonal] dysfunction, or both; and…will not cause brain tumors.” However, the FDA’s own Public Board of Inquiry withdrew their approval over cancer concerns. “Further[more], several FDA scientists advised against the approval, citing [the aspartame company’s] own brain tumor tests.” The Commissioner approved aspartame anyway, before he left the FDA, and enjoyed a “$1,000/day” consultancy position with the aspartame company’s PR firm. Then, “the FDA…actually prevented the National Toxicology Program…from doing” further cancer testing.

So, we were left with people battling over different rodent studies, some of which showed increased cancer risk, and some of which didn’t. Reminds me of the whole saccharin story, where it caused bladder cancer in rats, but not mice, leaving us with unanswerable questions like: so, are we more like a rat? Or, a mouse? We obviously had to put the aspartame question to the test in people, but the longest human safety study lasted only 18 weeks. We needed better human data.

Since the largest rat study highlighted lymphomas and leukemias, the NIH-AARP study tracked blood cancer diagnoses. And, “[h]igher levels of aspartame intake were not associated with the risk of…cancer.” It’s a massive study, but was criticized for only evaluating relatively short-term exposure; people were only studied for five years. Hey—better than 18 weeks. But, how about 18 years?

All eyes then turned to Harvard, which started following the health and diets of medical professionals since before aspartame even came on the market. “In the most comprehensive long-term [population] study to evaluate the association between aspartame intake and cancer risk in humans,” they did find an “association between [both] diet soda and total aspartame intake and [the risk] of [both non-Hodgkin’s lymphoma] and multiple myeloma in men and leukemia in both men and women.”

Okay, but, why more cancer in men than women? A similar result was found for pancreatic cancer and diet soda, but not soda in general. In fact, the only sugar tied to pancreatic cancer risk here was the “milk sugar lactose.” It was the diet soda. So, the female/male discrepancy could have just been a statistical fluke. But, they decided to dig a little deeper.

Aspartame is broken down into methanol, and the methanol is turned into formaldehyde, “a documented human carcinogen” by this enzyme here, alcohol dehydrogenase. The same enzyme that detoxifies regular alcohol is the same enzyme that converts methanol to formaldehyde.

Is it possible men just have higher levels of this enzyme than women? Yes, that’s why women get higher blood alcohol levels drinking the same amount of alcohol. If you look at liver samples from men and women, there’s significantly greater enzyme activity in the men. So, maybe that explains the increased cancer risk in men—the higher conversion rates from aspartame to formaldehyde. But how do we test it?

Well, ethanol—regular alcohol—competes with methanol for this same enzyme’s attention. In fact, regular alcohol is actually “used as an antidote for methanol poisoning.” So, men who don’t drink may have higher formaldehyde conversion rates from aspartame if this whole formaldehyde theory is correct, and indeed, consistent with this line of reasoning, it was the men that drank the least alcohol that appeared to have the greatest cancer risk from aspartame.

A third cohort study has since been published, and found no increased lymphoma risk associated with diet soda during a ten-year follow-up period. So, no risk detected in the 18-week study, the 5-year study, or the 10-year study—only in the 18-year study. What should we make of all this?

Some have called for a “re-evaluation” of the safety of aspartame. The horse is kind of out of the barn at this point, with “34,000,000 pounds” of the stuff produced annually, but that doesn’t mean we have to eat it—especially, perhaps, pregnant women and children.

Please consider volunteering to help out on the site.

Image credits: Emw via WikimediaImages and https://pixabay.com/en/aspartame-sweetener-molecule-model-884052 via pixabay. Images have been modified.

Doctor's Note

What about the noncancer effects on the brain? See my video Aspartame & the Brain.

What about Splenda? Got a video on that, too: Effect of Sucralose (Splenda) on the Microbiome.

Is there any nontoxic low-calorie sweetener? Erythritol is probably the best candidate; see Erythritol May Be a Sweet Antioxidant—though we should probably get away from intense sweeteners, artificial or not. See, for example, Unsweetening the Diet.

More on the potential adverse effects of drinking diet soda in Does Diet Soda Increase Stroke Risk as Much as Regular Soda?

How about this for a calorie-reduction strategy instead? See Eating More to Weigh Less.

If you haven’t yet, you can subscribe to my videos for free by clicking here.

43 responses to “Does Aspartame Cause Cancer?

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  1. Wondering if you could touch upon the herpes virus and the vegan diet. Since going vegan I have had reoccurring outbreaks of cold sores? I did get them before but now it is week after week. Thanks so much I love all you videos and your book!




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    1. Micca, I have to watch out for this, too. Foods that are high in the amino acid arginine stimulate the herpes virus, which causes cold sores, shingles, and other forms of herpes outbreaks. Many of thos e foods are those we love as whole foods plant based eaters. Foods with the highest arginine levels are most nuts, seeds, chocolate and oatmeal. There are others, but levels aren’t as high. If you eat a lot of nut butters, they could be the culprit.

      Most of the time I can keep the virus under wraps by taking the amino acid L Lysine, which opposes arginine. I have to take 2,000 mg daily, on an empty stomach. Even so, if I get into the nuts too heavily, it will stimulate an outbreak. The minute I feel it coming on, I take 3,000 mg about three times that day and lay off the high arginine foods. I then back the dose off a bit, but still take more than my maintenance dose for a few days. This usually stops the outbreak before it gets a good start.




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    2. I had a similar problem, went from 1 cold sore outbreak a year to every few weeks. Managed to resolve it by cutting out peanuts and taking a lysine supplement (1000mg a day) – have now had only 1 in the last 10 months and even that only lasted a few days.




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    3. Someone else mentioned lysine but I’m wondering if now you’re vegan you’re eating more nuts and sesame seeds and the like? This is what I did as it’s an easy way to pump up the calories. Anyway, long story short is that they tend to be higher in argenine which can encourage outbreaks, lysine however is the opposite. A bit simplified but cut back on your nuts. That’s assuming that you’re otherwise eating a healthy well planned vegan diet.




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      1. Yeah, you’re probably right and I don’t have a problem with aspartame the way I do sugar, sucralose and high fructose corn syrup; not necessarily in that order; xylitol is awesome for me as are some other sweeteners




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    4. Micca, this happened to me as well, and I have to agree with the other responses that the arginine content of nuts/seeds is most likely to blame. Unfortunately, those of us who get cold sores should probably restrict this amino acid as much as possible. I personally found that when I cut out all nuts and seeds except a handful of cashews per day or less (cashews are the lowest in arginine of all nuts, by almost an order of magnitude in some cases), I haven’t had an outbreak since. Some sources will tell you that it’s the ratio of arginine to lysine that really matters because they compete for uptake in the body, so I have a suspicion that when we cut out the highest source of lysine in the diet (dairy), it exacerbates the problem. I find walnuts, chocolate, sesame seeds, and pumpkin seeds to be almost guaranteed triggers in addition to UV light, orange juice, and beer. It feels like such a curse sometimes that some of my favorite foods are off limits. Good luck, I know how frustrating it is to work hard to eat healthier and feel like it’s backfired with cold sores.




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    5. Hello Micca! Yes L-Lysine @1000mg tabs….2tabs every 4-6 waking hrs works for me to prevent an outbreak of Cold Sores and genital herpes also…You can find L-Lysine at almost any supplement store. I prefer to purchase at Vitacost.com since they are relatively cheap for cost and they sell the major brands(Solgar) plus their own….for an active infection stay away from Peanut butter and most nuts/nut butters as it has alot of of the amino acid L-Arginine which fuels the replication of the herpes virus. Thus, making your outbreaks worse and delaying healing. I have no connection to Vitacost.com in any way, shape, or form. Just a helpful science guy wishing you well. Best Wishes




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      1. Hi, Barbara. I am Christine, a NF volunteer nutrition moderator. Yes, I have heard this before, but the research is inconsistent, and appears to be limited to animal and in vitro studies, not studies in humans. You might be interested in these: https://www.ncbi.nlm.nih.gov/pubmed/19088459
        http://www.clinicaltherapeutics.com/article/S0149-2918(12)00382-7/abstract
        The amounts of Lysine given to the mice in the first study were enormous, much more than I have ever known a human to take, and they did not significantly affect cholesterol levels.
        For tips on lowering cholesterol, check out the Ask The Doctor page on NutritionFacts.org about lowering cholesterol for the person who has tried everything: http://nutritionfacts.org/questions/what-can-i-do-to-lower-my-cholesterol-it-seems-ive-tried-everything/
        I hope that helps!




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        1. Hi, Christine. Thank you so much for this information! I finally had a chance to read through everything, and it certainly put my mind at ease re: supplementing lysine. Thanks again.




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  2. The great aspartame-FDA conspiracy has been solved. Great video NF team for solving the ADH enzyme issue in men vs women.

    Today I learned (TIL) that methanol (diet soda) will slowly kill you almost exactly like ethanol (alcohol)!




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  3. Hi Micca,
    You might want to research L-Lysine supplementation and herpes virus. It is linked to reducing frequency, severity and duration of outbreaks.




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  4. No higher risk in 18 months, 5 years or 10 years, but higher risk in 18 years IF YOU drink LESS alcohol. “It was the men who drank the LEAST alcohol, the ones who had the highest risk of cancer from aspartame”. How much aspartame in 18 years?




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  5. I am Cancer free from Prostate cancer. It has been 4 years. I use to drink 3 Big Gulps a day of diet Coke and the aspertame was killing me. My cancer dr said that was probably the reason I had the prostrate cancer is because of the aspertame. Folks stay away from that stuff.




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    1. Thanks for your comment Wayne.

      First of all, I am really happy that you are cancer free, that is the most important factor and I wish you the best.

      At NF, we have some great resources for prostate cancer if you are interested, please see and explore each link here.

      Hope this helps.




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    2. I’d be that way with sucralose and aspartame together or just plain sucralose; likewise, people with beer and sucralose yogurts can easily get a big belly; I have no problem with plain aspartame any more than some people love 1/2-3/4ths of a banana every now and then – I’d focus on the L-Phenylalanine or whatever




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  6. I think there are some issues with the main (18 year) study cited and the formaldehyde claims:

    “We also observed an unexpected elevated risk of NHL (RR: 1.66; 95% CI: 1.10, 2.51) with a higher consumption of regular, sugar-sweetened soda in men but not in women”

    So any type of soda creates higher risk in men but not women (the additional enzyme in men doesn’t account for increased risk associated with regular soda)? That doesn’t seem to make sense unless I’m missing something (and I truly may be missing something – I’m not a scientist).

    “In contrast, when sexes were analyzed separately with limited power, neither regular nor diet soda increased risk of leukemia but were associated with increased leukemia risk when data for men and women were combined (RR for consumption of ≥1 serving of diet soda/d when the 2 cohorts were pooled: 1.42; 95% CI: 1.00, 2.02).”

    Again I’m no scientist, but it sounds like the diet soda didn’t actually increase risk, but instead was only associated with increased risk and only when men and women were combined. Does this makes sense to anybody? I’m not being snarky, I promise, it just doesn’t make sense to me. Maybe someone can explain it to me.

    Finally there’s this:

    “Although our findings preserve the possibility of a detrimental effect of a constituent of diet soda, such as aspartame, on select cancers, the inconsistent sex effects and occurrence of an apparent cancer risk in individuals who consume regular soda do not permit the ruling out of chance as an explanation”

    This doesn’t sound strongly conclusive to me.

    In regards to formaldehyde, it is found in lots of different foods. For instance the formaldehyde content of pears can vary from 38-60mg per kg, whereas aspartame is 61mg per kg. A 12 ounce can of diet soda has 225mg of aspartame which would result in 13.7 mg of formaldehyde which is less than half of the average pear.

    So are pears a carcinogen then? Cauliflower has 27mg of formaldehyde per kg, beetroot has 35mg of formaldehyde per kg. Furthermore the body makes formaldehyde on its own. Here is what the American Cancer Society says:

    “Formaldehyde is normally made in the body. Enzymes in the body break down formaldehyde into formate (formic acid), which can be further broken down into carbon dioxide.”

    I know I sound like PR guy for aspartame, but I’m not. Here’s my background:

    I’m just a regular guy who used to drink A LOT of diet coke (I don’t drink it anymore save for rare occasions) and I heard all the warnings about the dangers of aspartame. So I did a lot of research about it. Despite many organizations trying to demonize it, the science never seemed to indicate that it was dangerous. And for me it’s all about the science (that’s why I like Dr. Greger – he’s all about the science).

    So here we have a study that finds regular soda is associated with increased cancer risk in men as much as diet soda is, yet when men and women are evaluated separately diet soda doesn’t increase cancer risk and in conclusion all the findings may be completely chalked up to chance. This doesn’t sound like solid science you can hang your hat on.

    Then the video talks about formaldehyde and only calls it a carcinogen without giving any perspective such as the body makes it, and it’s found in greater quantities in regular foods like pears and cauliflower than in diet soda.

    As I mentioned before, I’m not a scientist just a skeptical guy, and I may be missing something and I’m truly open to someone explaining what I got wrong or missed. I want to specify I’m not stating diet soda is good for you, I just don’t think the current science on it being a carcinogen is in any way conclusive.




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    1. Informative post, Rod thanks.

      Yes, this does sound strange – maybe someone who has studied statistics / epidemiology could explain it to us?

      The only (odd) thing that I could think of to explain the findings, is perhaps diet soda actually DECREASES the cancer risk in women & causes the discrepancy when male & female stats are combined…!?




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  7. Is aspartame a whole plant food? This topic illustrated the beauty of a WFPB diet. Once you get fully onboard, you have to ask “why would anybody eat something like this anyway?”. It just doesn’t make sense, cancer or no cancer.




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    1. Thanks for your question.

      According to the Oxford Dictionary:

      Aspartame is defined as:

      “A very sweet substance used as an artificial sweetener, chiefly in low-calorie products. It is a derivative of aspartic acid and phenylalanine.”

      Whereas, whole foods is defined as:

      “Food that has been processed or refined as little as possible and is free from additives or other artificial substances.”

      Therefore, I would not consider it a whole food. Hope this answer helps.




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    1. Thanks Dan. I clicked on your link and enjoyed reading: “… the amount of glycine available from synthesis, about 3 g/day, together with that available from the diet, in the range 1.5-3.0 g/day, may fall significantly short of the amount needed for all metabolic uses, including collagen synthesis by about 10 g per day for a 70 kg human. This result supports earlier suggestions in the literature that glycine is a semi-essential amino acid and that it should be taken as a nutritional supplement to guarantee a healthy metabolism.”

      I prefer to eat my amino acids in their original whole food carriers, yet “enjoy the occasional indulgence” as Dr. G says.

      –A sweetener that is also a nutrient and promotes collagen synthesis… too good not to research further.




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    1. Hi Cheryl!

      I’m one of the NF.org moderators answering questions. I found a couple of additional NutritionFacts.org videos that may answer your question about stevia. Here are the links: http://nutritionfacts.org/video/is-stevia-good-for-you/ and http://nutritionfacts.org/video/a-harmless-artificial-sweetener/

      Dr. Greger also writes about stevia in his book How Not to Die. Typically I would quote what he says in his book but unfortunately I don’t have my copy handy right now. So, if the videos above don’t give you what you want let me know and I’ll get back to you with the information in the book.

      Corey – NutritionFacts.org moderator




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  8. It’s hard for me to fathom that the dangers of aspartame are debateble. Then there’s all of those gulf war vets that got poisoned badly from consumption of the cases of diet soda baking in the desert sun.




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    1. Barbara Dinoff: My understanding is that individuals from the public vote on the videos. The number of stars you see is the average of the individual votes.




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