Stevia: The Plant-Derived Glycoside
Stevia is sourced from the leaves of the Stevia rebaudiana plant, native to South America, where it has been used for centuries. The sweet taste comes from a group of natural compounds within the plant called steviol glycosides.
These compounds include stevioside, rebaudioside A (often labeled as 'Reb-A' on products), and others. Steviol glycosides are intensely sweet, often hundreds of times sweeter than table sugar (sucrose), but are not metabolized by the human body. Instead, they pass through the digestive system largely unchanged, which is why they contribute no calories and have a glycemic index of zero.
The Chemical Structure of Steviol Glycosides
Chemically, a steviol glycoside consists of a steviol molecule attached to one or more glucose molecules. Steviol is a diterpene compound, and the attached sugars make it a glycoside. It is this glycoside structure, rather than a polyol structure, that defines stevia.
Polyols: Understanding the Sugar Alcohols
Polyols, or sugar alcohols, are a different class of organic compounds. They are carbohydrates with a chemical structure that resembles both sugar and alcohol, but they contain no ethanol.
Common examples of polyols include:
- Erythritol: Found naturally in some fruits and fermented foods. It is not fully absorbed by the body, leading to a minimal caloric load and impact on blood sugar.
- Xylitol: Often sourced from corn or birch bark.
- Sorbitol: Found naturally in many fruits, including apples and pears.
- Maltitol: Often used in sugar-free candies and baked goods.
Unlike stevia, polyols are a form of carbohydrate, albeit one that is not fully digested. The partial absorption is what gives polyols fewer calories than sugar but can also lead to gastrointestinal issues for some individuals.
The Commercial Blending of Stevia and Polyols
So why is the question "Is stevia a polyol?" so common? Many commercially available sweeteners that market themselves as "stevia-based" actually contain a blend of stevia extract and a polyol, most often erythritol.
This blending is done for a few key reasons:
- Bulk: Stevia extract is hundreds of times sweeter than sugar and is needed in tiny quantities. Polyols are added to provide the bulk and volume that makes the product easy to measure and use as a one-to-one sugar replacement in baking and cooking.
- Taste Profile: While some find pure stevia to have a slightly bitter, licorice-like aftertaste, polyols like erythritol can help to balance and round out the flavor, making it more palatable.
- Cost: Blending can be a cost-effective way to produce a popular sweetener alternative.
Comparison: Stevia vs. Polyols
| Feature | Stevia (Steviol Glycosides) | Polyols (Sugar Alcohols) |
|---|---|---|
| Chemical Type | Glycoside (not a sugar alcohol) | Carbohydrate (sugar alcohol) |
| Source | Stevia rebaudiana plant leaves | Fruits, vegetables, fermentation |
| Calories | Zero | Fewer than sugar (0–3 calories per gram) |
| Metabolism | Not metabolized; excreted from the body | Partially absorbed and metabolized |
| Glycemic Index | Zero | Low, but can vary by type |
| Potential Side Effects | Generally considered safe; potential interaction with medications, bitterness | Gastrointestinal issues (bloating, gas, diarrhea) for some |
Conclusion
In summary, stevia is not a polyol. The confusion arises because these two distinct types of sweeteners are frequently combined in commercial products to improve taste and usability. Stevia is a natural, non-nutritive sweetener derived from the stevia plant's leaves, while polyols, or sugar alcohols, are a class of carbohydrates that are only partially absorbed by the body. Understanding this key difference is essential for consumers, especially those with sensitivities to sugar alcohols or specific dietary needs. When purchasing, it is important to check the ingredients list to see if the product contains pure stevia extract or a blend with polyols. This helps ensure you are getting exactly the sweetener you intend to use.
For additional information on steviol glycosides, their safety, and potential therapeutic effects, the National Institutes of Health provides extensive research summaries.
