Steviol glycosides are the naturally occurring compounds in the stevia plant that make it sweet. They are 110 to 400 times sweeter than table sugar, contain zero calories, and serve as the active ingredients in stevia-based sweeteners found on grocery store shelves worldwide. Despite their intense sweetness, these compounds don’t raise blood sugar the way sucrose does, which is a major reason they’ve become one of the most popular sugar alternatives.
The Chemistry Behind the Sweetness
Every steviol glycoside shares the same core structure: a molecule called steviol. What makes each one different is the type and number of sugar units attached to that steviol backbone. These sugar units can include glucose, fructose, xylose, and rhamnose, among others, and they attach at two specific positions on the molecule. The particular combination of sugars at those positions determines which steviol glycoside you get, how sweet it tastes, and whether it has a bitter or licorice-like aftertaste.
The two most abundant steviol glycosides in the stevia leaf are stevioside and rebaudioside A (often labeled Reb A). Stevioside makes up roughly 4 to 13% of dried stevia leaves and is 110 to 270 times sweeter than sucrose, though it carries a noticeable bitter aftertaste. Reb A, present at about 2 to 4% of the dried leaf, is 250 to 400 times sweeter and tastes cleaner. A newer glycoside called Reb M has gained attention because it closely mimics the taste of sugar without the bitterness that plagues stevioside. In ice cream taste tests, Reb M received sweetness ratings comparable to sucrose, with no statistically significant difference.
How They’re Extracted and Produced
The traditional method for obtaining steviol glycosides is straightforward: dried stevia leaves are steeped in hot water, much like brewing tea. Optimized extraction uses water heated to about 75°C (167°F) with a steeping time of around 20 minutes. The liquid is then filtered through membranes to concentrate the sweet compounds and remove plant material. No harsh chemical solvents are required. The process aligns with green chemistry principles, since the only extractant is water.
For glycosides like Reb M that exist in very small quantities in the leaf, simple extraction isn’t practical. Instead, manufacturers use enzymatic bioconversion. Enzymes derived from soil bacteria can attach additional sugar units onto more common glycosides like stevioside or Reb A, converting them into Reb M. This process uses starch as the sugar donor and specialized enzymes called cyclodextrin glucanotransferases to build up the molecule. Some companies also use fermentation, engineering yeast to produce steviol glycosides directly. These bioconversion methods make it commercially viable to produce the best-tasting glycosides at scale.
How Your Body Processes Them
Steviol glycosides pass through your mouth, stomach, and small intestine completely intact. The digestive enzymes in your saliva, stomach acid, and pancreas cannot break them apart. They arrive in the colon unchanged, where specific gut bacteria, primarily from the Bacteroides group, strip away the sugar units and release the steviol backbone. Other common gut bacteria like Lactobacilli and Bifidobacteria cannot perform this step.
Once freed, steviol is absorbed through the intestinal wall and travels via the bloodstream to the liver. There it gets converted into a compound called steviol glucuronide, which is then excreted in urine. This metabolism pathway is important because it means steviol glycosides don’t accumulate in the body and don’t contribute calories at any point in the process.
Effects on Blood Sugar and Insulin
Replacing sugar with steviol glycosides does not spike your blood glucose. When people drink a stevia-sweetened beverage with a meal instead of a sugar-sweetened one, both blood sugar and insulin responses after the meal are lower. This holds true for healthy adults as well as people with type 2 diabetes.
A meta-analysis reviewing 26 studies found that stevia consumption was associated with a modest but significant reduction in blood glucose levels, particularly in people with higher BMI, diabetes, or hypertension. The effect appeared within one to four months of regular use. However, stevia did not significantly affect long-term markers like HbA1c (a measure of average blood sugar over three months) or fasting insulin levels. In other words, steviol glycosides can help blunt post-meal sugar spikes, but they aren’t a treatment for diabetes on their own.
Effects on Dental Health
Unlike sugar, steviol glycosides are non-fermentable, meaning the bacteria in your mouth cannot feed on them to produce the acid that causes cavities. Research suggests stevia may actually be anticariogenic, actively working against tooth decay. In a pilot study comparing stevia chewing gum to xylitol chewing gum (a well-established tooth-friendly sweetener), both were equally effective at reducing levels of Streptococcus mutans, the primary bacterium responsible for cavities. Stevia also shows anti-plaque activity, which adds another layer of dental benefit beyond simply not causing harm.
Safety and Recommended Limits
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has set an acceptable daily intake of 0 to 4 mg per kilogram of body weight, expressed as steviol. For a 150-pound (68 kg) adult, that works out to about 272 mg of steviol per day, which translates to a large amount of stevia sweetener in practical terms. The FDA classifies high-purity steviol glycosides (95% or greater purity) as Generally Recognized as Safe.
JECFA noted that young children who are heavy consumers of stevia-sweetened foods could theoretically exceed the ADI by up to 10%, based on worst-case modeling that assumed maximum permitted use levels across every food category. But the committee considered this estimate highly conservative and concluded that steviol glycosides are not likely to present a health concern for any age group at real-world consumption levels.
Common Products and Labeling
On ingredient labels, you’ll see steviol glycosides listed under various names: stevia leaf extract, Reb A, rebaudioside M, stevioside, or simply “stevia extract.” Table-top sweetener brands typically blend a small amount of steviol glycosides with a bulking agent like erythritol or dextrose, since the glycosides are so intensely sweet that a pure form would be nearly impossible to measure in household quantities. Steviol glycosides are also heat stable, so they hold up in baking and cooking, unlike some artificial sweeteners that break down at high temperatures.