Allulose is a rare sugar, classified as a monosaccharide, or simple sugar, that tastes and functions much like table sugar but contains a fraction of the calories. Concerns about its digestive impact are common, especially since many low-calorie alternatives cause gas and bloating. The primary question is whether the body processes allulose in a way that leads to digestive discomfort, centering on how much bypasses the small intestine and reaches the gut bacteria.
What is Allulose and How is it Processed?
Allulose (D-psicose) is structurally similar to fructose but is metabolized very differently by the human body. Unlike common sugars, the body lacks the necessary enzymes to fully break down allulose for energy. Instead of being completely metabolized, a large portion of the ingested allulose is absorbed into the bloodstream.
Approximately 70% to 80% of the allulose consumed is absorbed in the small intestine, primarily through the same transport mechanism used for fructose, known as the GLUT5 transporter. Once absorbed, it is not used as fuel but is excreted unchanged through the urine, typically within 24 hours. This processing is why allulose contributes only a negligible amount of calories (about 0.2 to 0.4 calories per gram), compared to the 4 calories per gram found in regular sugar.
The remaining 20% to 30% of the ingested allulose is not absorbed in the small intestine and continues into the large intestine. This unabsorbed fraction interacts with the gut microbiome. Because allulose is not absorbed for energy and does not significantly raise blood sugar levels, it is a favored sweetener for those managing diabetes or following low-carbohydrate diets.
The Mechanism Behind Digestive Discomfort
The digestive discomfort associated with allulose, including gas and bloating, stems from the portion that reaches the large intestine. Any carbohydrate not fully absorbed in the small intestine passes into the colon, where it is exposed to gut bacteria. These bacteria attempt to break down the unabsorbed allulose through a process called fermentation.
This bacterial fermentation process generates gases that lead to symptoms like abdominal distention, cramping, and flatulence. The gases produced are primarily hydrogen, carbon dioxide, and, in some people, methane. This mechanism is comparable to how other poorly absorbed carbohydrates, such as certain sugar alcohols and fermentable fibers, cause gastrointestinal upset.
In addition to gas production, consuming high amounts of allulose can have an osmotic effect. This means the unabsorbed sugar in the intestines draws water into the colon, which can accelerate bowel movements and lead to loose stools or diarrhea. Symptoms such as diarrhea, abdominal distention, and abdominal pain occur more often following high-dose allulose intake compared to regular sugar. The severity of these side effects is directly related to the amount consumed in a single serving.
Managing Intake to Prevent Digestive Issues
Since digestive side effects are dose-dependent, consumers can mitigate potential discomfort by carefully managing their intake. Scientific studies have established clear thresholds for allulose tolerance in healthy adults. The recommended maximum single dose to avoid severe gastrointestinal symptoms is 0.4 grams of allulose per kilogram of body weight.
For a person weighing 150 pounds (approximately 68 kilograms), this single-serving limit translates to about 27 grams of allulose. The maximum total daily intake suggested for regular consumption is 0.9 grams per kilogram of body weight (about 61 grams for a 150-pound individual). Exceeding the single dose limit, particularly at 0.5 grams per kilogram, has been shown to consistently produce severe diarrhea.
Individual tolerance varies greatly, so it is beneficial to introduce allulose gradually into the diet. Starting with a small amount and slowly increasing the dosage allows the body to adapt to the new substance. Adhering to the established limits and being mindful of the total amount consumed throughout the day are practical steps to enjoy allulose as a sweetener while preventing uncomfortable digestive side effects.