Steviol glycosides are the naturally occurring sweet compounds found in the leaves of the stevia plant. They’re what make stevia taste sweet, and they’re 150 to 450 times sweeter than table sugar depending on the specific type. When you see “stevia” on a food label, the actual sweetening ingredient is one or more of these glycosides, extracted and purified from the plant’s leaves.
How They Create Sweetness
All steviol glycosides share the same core: a molecule called steviol, which is a type of diterpene. What distinguishes each glycoside from the others is the number and arrangement of sugar molecules attached to that core. More than 30 different steviol glycosides have been identified in stevia leaves, but a handful dominate commercial use.
Stevioside is the most abundant glycoside in the leaf and is roughly 150 to 300 times sweeter than sugar. Rebaudioside A (often listed as Reb A on labels) is the most widely used in food products, clocking in at 250 to 450 times sweeter than sugar. The catch with both is that they also trigger bitter taste receptors, specifically receptors called TAS2R4 and TAS2R14, which is why many people notice a bitter or licorice-like aftertaste with stevia products.
Newer glycosides are changing that. Rebaudioside M, a minor component of the leaf, has a cleaner taste profile. In sensory panels, it showed faster sweetness onset and significantly less bitterness, astringency, and lingering off-flavors compared to Reb A. Molecular simulations suggest Reb M is simply too large to interact with the TAS2R4 bitter receptor, which explains why trained tasters detected no significant bitter or licorice taste even at high concentrations.
What Happens When You Eat Them
Your body handles steviol glycosides differently from sugar or most other sweeteners. They pass through your mouth, stomach, and upper digestive tract completely intact. Digestive enzymes like amylase, pepsin, and pancreatin can’t break them down.
The real processing happens in your lower gut. Specific bacteria, primarily from the Bacteroides group, strip the sugar molecules off the steviol core. Other common gut bacteria, including Lactobacilli, Bifidobacteria, and E. coli species, can’t perform this step. Once freed, the steviol is absorbed through the intestinal wall, travels to the liver via the portal vein, gets converted into a compound called steviol glucuronide, and is excreted in urine. Nothing accumulates in the body.
Effects on Blood Sugar and Insulin
Steviol glycosides don’t raise blood sugar. In a controlled study comparing stevia, aspartame, and sucrose, participants who consumed stevia before a meal had significantly lower blood glucose levels than those who consumed sugar. The differences appeared as early as 20 minutes after consumption and persisted through 30 and 60 minutes after a follow-up lunch.
What’s more notable is the insulin response. Stevia produced lower insulin levels than both sugar and aspartame. Insulin was significantly reduced at 20 minutes after the stevia preload and remained lower at 30 and 60 minutes after the meal. This makes steviol glycosides particularly relevant for people managing blood sugar, since they satisfy sweetness without triggering the hormonal cascade that sugar does.
How They’re Extracted From the Plant
Commercial steviol glycosides start as dried stevia leaves. In a basic extraction, leaves are soaked in hot water (around 40°C) for a couple of hours, which pulls the glycosides into solution. The liquid then goes through purification steps to isolate specific glycosides and remove plant matter, chlorophyll, and other compounds.
Modern purification uses techniques like resin adsorption, ion exchange, and recrystallization to achieve the high purity levels required for food use. For rare glycosides like Reb M, the yield from leaves is tiny. In one research extraction, two kilograms of dried leaves produced just 1.1 grams of purified Reb M. That scarcity is why some manufacturers now produce minor glycosides through fermentation or enzymatic conversion rather than direct leaf extraction.
Safety and Regulatory Status
High-purity steviol glycoside extracts (95% purity or above) have FDA “no questions” GRAS status, meaning the agency has reviewed safety data and doesn’t object to their use in food. This applies to specific purified glycosides, not crude stevia leaf or whole-leaf extracts, which don’t carry the same regulatory clearance.
The Joint FAO/WHO Expert Committee on Food Additives has set an acceptable daily intake of 0 to 4 mg per kilogram of body weight per day, expressed as steviol equivalents. For a 70 kg (154 lb) person, that’s up to 280 mg of steviol equivalents daily, which translates to a substantial amount of stevia-sweetened food and beverages before you’d approach the limit.
Stability in Cooking and Beverages
Steviol glycosides hold up well under most kitchen and manufacturing conditions. As a dry powder, stevioside remains stable up to 120°C (248°F). Above 140°C (284°F), it starts to break down. In liquid form, the glycosides are remarkably resilient across a pH range of 2 to 10 at temperatures up to 80°C (176°F), with less than 5% degradation after two hours of heating. That covers nearly every common cooking scenario, from acidic fruit drinks to baked goods.
The one vulnerability is extreme acidity. At pH 1, which is more acidic than any typical food or beverage, stevioside breaks down completely when heated to 80°C for two hours. In practical terms, this isn’t a concern for home cooking or standard food production, but it does matter for highly acidic industrial formulations.
Why Labels List Different Types
If you’ve noticed ingredient lists specifying “Reb A” or “Reb M” rather than just “stevia,” that’s because each glycoside has a distinct taste and sweetness profile. Products built around Reb A are the most common and least expensive, but they’re more likely to carry that characteristic stevia aftertaste. Blends that include Reb D or Reb M cost more to produce but deliver a taste closer to sugar, with less bitterness and a more natural sweetness curve. Some products combine multiple glycosides or pair them with other sweeteners like erythritol to mask residual off-flavors and build a more rounded sweetness.