Steviol is a diterpene compound found exclusively in the leaves of the Stevia rebaudiana plant, native to South America. This molecule forms the structural base for a family of intensely sweet compounds known as steviol glycosides. For centuries, the leaves of the stevia plant have been used by indigenous populations to sweeten local beverages and foods. The primary application of the extracted steviol glycosides today is as a high-intensity, non-caloric sweetener alternative to traditional sugar.
Steviol Glycosides: Source and Extraction
The sweet sensation associated with the stevia plant comes from the various steviol glycosides present in the leaf tissue, such as Stevioside and Rebaudioside A. These glycosides are formed when sugar molecules are attached to the core steviol structure. These natural compounds are significantly sweeter than sucrose, with sweetness intensity ranging from 40 to over 300 times that of sugar.
Extraction begins with harvesting and drying the stevia leaves, which are then typically steeped in hot water. Water-based extraction is a common method, though ethanol-water mixtures can also be used to draw the sweet compounds out of the plant material. The resulting crude liquid extract contains a complex mix of steviol glycosides, along with plant pigments, waxes, and other non-sweet components.
To create commercial sweetener products, this crude extract must undergo an extensive purification process to remove bitter-tasting compounds. Clarification steps often involve using agents like activated charcoal or membrane filtration techniques, such as ultrafiltration and nanofiltration, to separate the glycosides from impurities. Further refinement involves crystallization, where the purified solution is concentrated to isolate high-purity steviol glycosides, resulting in a product that typically contains at least 95% total steviol glycosides.
How the Body Processes Steviol
The zero-calorie nature of steviol glycoside sweeteners is directly related to how the human body handles them physiologically. When consumed, the large, complex steviol glycoside molecules are not broken down or absorbed in the upper gastrointestinal tract, including the stomach and small intestine. This non-absorption occurs because human digestive enzymes are unable to cleave the sugar units from the steviol backbone.
The intact glycosides continue their journey until they reach the colon, where the gut microbiota, specifically certain anaerobic bacteria, are capable of metabolizing them. These bacteria possess enzymes that hydrolyze the sugar molecules, releasing the core molecule, which is free steviol. This released steviol is then absorbed into the bloodstream.
Once absorbed, the steviol is rapidly processed by the liver, where it undergoes a detoxification process called glucuronidation. The liver attaches a molecule called glucuronic acid to the steviol, creating a water-soluble compound known as steviol glucuronide. This compound is then efficiently excreted from the body via the urine, preventing any accumulation of steviol or its metabolites. Because the steviol glycosides are neither absorbed nor utilized for energy before excretion, they contribute a negligible amount of calories.
Global Regulatory Acceptance and Safety
Highly purified steviol glycosides have been extensively reviewed by major international food safety and regulatory bodies, leading to their global acceptance as a safe food additive. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) established a safety standard for the compounds. The U.S. Food and Drug Administration (FDA) has determined that high-purity steviol glycosides are Generally Recognized As Safe (GRAS) for use in foods and beverages.
The European Food Safety Authority (EFSA) and JECFA have both established an Acceptable Daily Intake (ADI) for steviol glycosides, expressed as steviol equivalents, at 4 milligrams per kilogram of body weight per day. This ADI is set using a 100-fold safety factor applied to the no-observed-adverse-effect level (NOAEL) found in long-term animal studies. This level represents an amount that can be consumed daily over a person’s lifetime without any appreciable health risk.
A distinction must be made between the approved, highly purified extracts and the crude stevia leaf or unpurified extracts. Regulatory bodies, including the FDA, have not approved the use of whole stevia leaves or crude extracts as sweeteners due to a lack of safety data regarding all the various components present in the unrefined material. The approval is specifically for the purified steviol glycosides that meet strict compositional specifications, ensuring a consistent and safe product for consumers worldwide.