Xylitol: Safe or harmful?

Xylitol is growing in popularity as a natural sugar substitute to sweeten various foods, gums, and oral care products. However, if you search the internet you find reports that xylitol is harmful and shouldn’t be consumed. So, what are the facts? Is xylitol a safe natural sweetener and sugar substitute with potential health benefits, or is it a toxic ingredient that should be avoided? Read on to discover the scientific facts of this often maligned sweetener.

What is xylitol?

This discussion needs to start with what xylitol is. Xylitol is a 5-carbon sugar alcohol (also called polyols) that has a crystalline, granular structure and sweetness comparable to sugar. Despite containing the name alcohol, xylitol contains no ethanol like alcoholic beverages. It is called a sugar alcohol like other sugar alcohols: sorbitol, mannitol, maltitol, isomalt, and lactitol  because its chemical structure places it in the alcohol family. It contains about 2.4 calories per gram (compared to 4 calories per gram for sugar). It is naturally found in some fruits and vegetables. Commercial xylitol is usually obtained from corn cobs or birch trees. Sugar alcohols are not processed the same as sugar absorbed and processed more slowly, which means that it provides fewer calories than the same amount of sugar and has less of an impact on blood sugar and insulin.

What is the problem or potential harm of xylitol and sugar alcohols?

Large amounts of sugar alcohols can cause gastrointestinal upset, such as gas, abdominal pain, and diarrhea.(1) However, the average person will not experience these effects unless they are consuming 50 grams or more per day. Indeed, research from the 1980s in the Soviet Union that administered 30 grams of xylitol per day observed that diarrhea and other side effects seldom occurred.(2) The same review of Soviet research concluded that xylitol is well-tolerated in children at doses of 20 to 35 grams daily for up to four weeks. People who are sensitive to sugar alcohols may experience GI symptoms — often severe — at much lower doses.

The most common report on blogs even among health professionals — is a concern about the toxicity of xylitol. This concern largely stems from animal research and appears to be misguided (more to come on this). It is important to remember that natural doesn’t always mean non-toxic. What determines toxicity is the dose of the substance (this principle is true of all substances regardless of whether it is natural or synthetic). A perfect example is water. Drinking too much water causes water intoxication (poisoning, seizures, and convulsions). Water is necessary to sustain life, but it can be toxic in excess. The same goes for many natural products, including xylitol.

What does research say?

Here is a brief summary of some of the research regarding toxicity in animals and humans.

  • Xylitol is extremely toxic to dogs (keep xylitol products away from man’s best friend) and can cause low blood sugar, seizures, liver failure, and death.(3)
  • Bladder tumors increased in mice when their diet consisted of 10% or 20% xylitol.(4) This is due to the conversion of a minor metabolite of xylitol called glycolic acid to oxalate. Increased oxalate in the urine predisposes mice to bladder stones, and in turn, bladder tumors. If humans consumed just 10% of their calories as xylitol, the average adult (based on a 2,000 calorie diet) would consume nearly 84 grams of xylitol daily. It would reach a whopping 167 grams if 20% of our calories came from xylitol.
  • At 20% of their diet, rats also experience an increased risk of tumor formation, but not at 10%.(4)
  • Humans do not readily convert glycolic acid to oxalate, and no increase in urinary oxalate levels has been observed even at doses of 1 g/kg body weight daily.(4) To put this in perspective, the average-sized person would need to consume 70 grams of xylitol daily to reach this level of consumption. Based on this no adverse effect, the study author concluded that humans exposed to normal levels of xylitol are at no risk of developing bladder tumors.

The current available research demonstrates that xylitol toxicity is species dependent, and not all animal studies can be directly correlated to humans. Current evidence in humans suggests it takes extreme amounts of xylitol to cause GI upset and potential harm.

Many products sweetened with xylitol (gum, breath mints, candy, protein powders) contain 1 gram or less of xylitol, meaning you would have to consume a significant amount of the products to even reach the safe level of 70 grams. Other products (jams/jellies — about 6 grams per tablespoon; baked goods) contain higher levels.

Benefits of xylitol

Research suggests that xylitol helps prevent tooth decay and cavities by preventing oral bacteria from sticking to teeth.(5) By preventing bacteria from sticking to teeth, xylitol reduces plaque formation. Remarkably, another review even found that xylitol can reverse the process of early cavities.(6) At least 5 grams of xylitol daily is necessary to produce a benefit to oral health, and some experts suggest 10 to 15 g in divided doses daily.(1) In addition, xylitol is a good choice for diabetics because it is low-glycemic and does not raise blood glucose or insulin levels like sugar.

Evidence-based conclusion

Based on the research and benefits of xylitol, it can be safely used in most adults at reasonable amounts (no more than 50 grams daily, but preferably less than 35 grams daily) and most children (less than 25 grams daily). Larger amounts may cause GI upset, while even small amounts may be problematic for sensitive individuals. Xylitol is beneficial for oral health, diabetics, and as a natural sugar substitute in reasonable doses, but should be avoided in excessive amounts.


REFERENCES

(1) Makinen KK. Gastrointestinal disturbances associated with the consumption of sugar alcohols with special consideration of xylitol: Scientific review and instructions for dentists and other health-care professionals. Int J Dent. 2016;2016:5697907.

(2) Nesterin MF. Xylitol. Experimental and clinical investigations conducted in the USSR (review). Z Ernahrungswiss. 1980 Jun;19(2):88-94.

(3) Cortinovis C, Caloni F. Household food items toxic to dogs and cats. Front Vet Sci. 2016;3:26.

(4) Roe FJ. Perspectives in carbohydrate toxicology with special reference to carcinogenicity. Swed Dent J. 1984;8(3):99-111.

(5) Janakiram C, Deepan Kumar CV, Joseph J. Xylitol in preventing dental caries: A systematic review and meta-analyses. J Nat Sci Biol Med. 2017 Jan-Jun;8(1):16-21.

(6) Nayak PA, Nayak UA, Khandelwal V. The effect of xylitol on dental caries and oral flora. Clin Cosmet Investig Dent.  2014 Nov 10;6:89-94.

4 replies
  1. John S
    John S says:

    Since xylitol is a natural sugar substitute, does that mean it doesn’t come from GMO corn cobs? Is commercial xylitol extracted somehow without the use of chemicals to keep it natural?

    Reply
    • Scott A. Johnson
      Scott A. Johnson says:

      It depends on where the manufacturer sources the xylitol. Many do source non-GMO corn cobs to extract xylitol from. However, some do extract from GMO corn, especially Chinese sources. Xylitol extraction typically involves adding the corn cobs to a natural acid solution.

      Reply
  2. Dallas Anderson
    Dallas Anderson says:

    So I have researched the xylitol side effects to find out whether it is really safe or not. First, because the body cannot digest them properly the non-metabolized portion ferments and creates a favorable environment for harmful bacteria to colonize.

    Reply
    • Scott A. Johnson
      Scott A. Johnson says:

      Hi, Dallas,

      I have heard this also, but could not find any good research to support this assertion. I did find one article that xylitol increased Prevotella bacteria in mice at a 5% xylitol diet (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3876090/). However, human studies don’t necessarily correlate with this finding. Can you provide research (in the form of a link to a published study) that supports this?

      Research with animals and humans suggests the opposite. A shift from gram-negative to gram-positive bacteria was observed in rodents and humans (https://www.ncbi.nlm.nih.gov/pubmed/4076932/). What has been reported in studies is that the fermentation of xylitol to low molecular weight osmotically active materials may cause short-term diarrhea in some people. Interestingly, people who experience diarrhea tend to have higher yeast levels in their gut as well. Scientists believe this plays a role in the observed diarrhea. Other research suggests that xylitol fermentation and rapid degradation of xylitol in the colon leads to significant increases in the production of short-chain fatty acids and a decreased production of branched-chain fatty acids, which favorably shifts metabolic patterns and colon microbes (https://www.ncbi.nlm.nih.gov/pubmed/17995737).

      Reply

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