How Sugar Alcohol Intake Impacts the Gastrointestinal System
by Eric Trexler, Ph.D.
When it comes to sugar alcohols, it’s important to take note of how your gastrointestinal system responds to different doses of specific sugar alcohols. As shown in the figure below, a significant portion of ingested sugar alcohol will contribute to fecal mass and fermented material in the colon (1). Notably, there are two major products of this fermentation process: short-chain fatty acids and gas (specifically a combination of hydrogen gas, carbon dioxide, and methane). As a result, sugar alcohols are often associated with flatulence and diarrhea. Having said that, both anecdotes and the published literature indicate that there is considerable inter-individual variability with regards to how specific doses and types of sugar alcohols impact flatulence and diarrhea (2). For example, xylitol and erythritol tend to be associated with less substantive gastrointestinal complaints in comparison to most other sugar alcohols, whereas maltitol (commonly found in low-sugar or sugar-free chocolates, candies, and protein bars) is commonly associated with notable gastrointestinal disturbances. Of course, with any particular sugar alcohol, the dose makes a huge difference. Most people find that small doses of sugar alcohols are quite tolerable – if they weren’t, these ingredients would’ve never caught on as viable food additives. However, just about any sugar alcohol consumed above a certain threshold will be likely to cause some degree of gastrointestinal distress, and the exact “limit” for each specific sugar alcohol tends to vary from person to person.
When comparing one sugar alcohol to another, some of the variation in gastrointestinal symptoms is related to the relative degree of absorption in the small intestine. For example, erythritol is typically well-absorbed in the small intestine and is generally associated with less gastrointestinal disturbance than other sugar alcohols (2). Less of the sugar alcohol reaches the colon when absorption is higher, which reduces the likelihood of both flatulence and diarrhea. As for the inter-individual variation in this area, it’s very plausible that differences between people may be linked to the gut microbiome, given that the bacterial composition of the gut microbiome will vary from person to person (3) and these bacteria are responsible for fermenting sugar alcohols that reach the colon. When it comes to intra-individual variation in gastrointestinal responses to any particular sugar alcohol, there are at least two critical factors: the gut microbiome (4), and the co-ingestion of other nutrients (2).
From a practical perspective, this reveals a couple of key inferences. First, your tolerance of a given dose of a specific sugar alcohol might be impacted by the makeup of your gut microbiome. Second, your tolerance of a given dose of a specific sugar alcohol might change over time, given that the gut microbiome is not remotely static (3). For instance, there is very high-quality evidence indicating that gastrointestinal symptoms from high-dose xylitol consumption drop dramatically with consistent ingestion (5). Third, your intake of sugar alcohols, which “feed” gut bacteria, may directly influence changes in your gut microbiome over time. As demonstrated by Hattori et al (4), specific gut bacteria are responsible for the fermentation of specific sugar alcohols, and the presence (or absence) of gut bacteria can significantly impact susceptibility to sugar alcohol-induced diarrhea. Just as there are data showing improved tolerance of xylitol over time, there are also data showing changes in the gut microbiome in response to consistent xylitol consumption (5). In summary, it appears that diarrhea is most likely to occur if you’re consuming a type of sugar alcohol that doesn’t align with the content of your gut microbiome, or if you’re consuming an amount that totally overwhelms the fermentation capacity of your gut bacteria.
So, let’s say you find the perfect protein bar. It’s affordable, it tastes great, it’s conveniently accessible at your grocery store, and it has great macros. You incorporate it into a quick snack on-the-go (let’s say an apple and a protein bar) and are disappointed to find that it causes diarrhea. I wouldn’t fault anyone for abandoning a food product that upset their stomach, but I would cautiously suggest that hope isn’t entirely lost. First and foremost, I would try consuming the same bar on an empty stomach with no other foods or beverages. Sugar alcohols are more likely to cause stomach discomfort when they’re co-ingested with other carbohydrates that compete for the same transporters or require fermentation, so removing the apple could make a big difference and help you determine if the sugar alcohol is really the sole cause of the issue. Even if the apple wasn’t a contributing factor, I wouldn’t be shocked if your gut microbiome adapted in response to consistent consumption of lower (more tolerable) doses of that specific sugar alcohol. This longitudinal adaptation may leave your gut more capable of metabolizing that sugar alcohol, leading to more complete fermentation and a lower likelihood of diarrhea as you escalate your “dose” of the sugar alcohol.
I also tend to find that mixing sugar alcohols is a suitable strategy in some contexts. For example, I prefer to aim for 30-40 grams of protein per meal at the moment, and many protein bars offer only 20 grams per bar. I’m particularly fond of two specific protein bar brands, and they happen to utilize different sugar alcohols. If I consumed two bars of either brand at a single meal, I might run into some gut-related issues. However, I do quite well when consuming one of each. So, if you wish you could tolerate protein bars but have had some bad experiences, you might consider an approach that aims to build tolerance over time or aims to utilize a combination of multiple distinct sugar alcohols. However, there are two caveats. First, know when to cut your losses – don’t give yourself diarrhea for six months out of false hope or stubbornness. Second, the concepts of building tolerance or combining sugar alcohols pertains to attenuating diarrhea specifically – I’m not convinced that we can do anything about the gas or bloating that comes with excessively high doses of sugar alcohols. If you are struggling to ferment the sugar alcohols you’re ingesting, then diarrhea will ensue. If you use the previously mentioned approaches to facilitate more complete fermentation of the sugar alcohols you’re ingesting, then gas formation in the colon will be an inevitable consequence of successful fermentation. In other words, increased gas production is the direct result of more successfully avoiding diarrhea in this particular scenario.
The biggest practical concern pertaining to sugar alcohol consumption is the management of gastrointestinal discomfort. There is considerable inter-individual variability with regards to how specific doses and types of sugar alcohols impact flatulence and diarrhea, and these differences may be related to the composition of a person’s gut microbiome at the time of digestion. If you don’t tolerate a specific sugar alcohol well, there’s nothing wrong with cutting it from your diet. Alternatively, you may find that you’re able to build tolerance to that sugar alcohol over time, or that a strategy of mixing sugar alcohols is more tolerable. While there might be creative strategies to attenuate or circumvent diarrhea-related side effects of sugar alcohol consumption, gas production is an inevitable consequence of metabolizing high doses of sugar alcohols.
References
- Grembecka M. Sugar Alcohols as Sugar Substitutes in Food Industry. In: Merillon JM, Ramawat KG, editors. Sweeteners: Pharmacology, Biotechnology, and Applications. Cham: Springer International Publishing; 2017. p. 1–27.
2. Lenhart A, Chey WD. A Systematic Review of the Effects of Polyols on Gastrointestinal Health and Irritable Bowel Syndrome. Adv Nutr. 2017 Jul 14;8(4):587-596.
3. Vandeputte D, De Commer L, Tito RY, Kathagen G, Sabino J, Vermeire S, et al. Temporal variability in quantitative human gut microbiome profiles and implications for clinical research. Nat Commun. 2021 Nov 18;12(1):6740.
4. Hattori K, Akiyama M, Seki N, Yakabe K, Hase K, Kim YG. Gut Microbiota Prevents Sugar Alcohol-Induced Diarrhea. Nutrients. 2021 Jun 12;13(6):2029.
5. Mäkinen 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. 2016:2016:5967907.