How is stevia metabolized
Stevia and steviol glycosides
Stevia rebaudiana Bertoni, also called honey herb or sweet herb, is a subtropical plant whose leaves taste sweet and are practically calorie-free. In Latin America, the leaves have been used to sweeten mate tea for hundreds of years. In the 1960s, Japanese companies discovered the sweet herb and paved the way for the stevia plant to be used on an industrial scale.
Sweeteners of natural origin can be obtained from the leaves of the stevia plant, which are summarized under the generic term "steviol glycosides" and are up to 300 times as sweet as table sugar. They were included in the list of sweeteners permitted as additives under number E 960. The stevia plant contains more than 30 different steviol glycosides, which can make up up to 20% of the dry weight. The best-known steviol glycosides with the largest proportion in the leaves are stevioside and rebaudioside A. Rebaudioside A is the compound with the highest sweetness and the purest taste.
Stevia sweeteners are available in powder, tablet and liquid form. Dried stevia leaves are also commercially available - for example as a bath additive. However, the use of pure stevia leaves as a food (additive) is still prohibited, as the leaves are composed differently depending on their origin. A safety assessment can only be carried out if the exact composition is known.
What are the benefits of steviol glycosides?
Steviol glycosides are practically calorie-free and tooth-friendly. They do not pose a threat to diabetics either: even higher doses do not affect blood sugar levels in diabetics, as steviol glycosides are metabolized independently of insulin. There is evidence from animal experiments that steviol glycosides may lower blood pressure.
For people who want to lose weight or want to avoid being overweight, sweeteners are a good alternative to sugar as part of a balanced diet.
At the same time, the taste and the so-called "mouth-feeling effect" are very similar to household sugar if the sweetener is made from high quality steviol glycosides. The mouth-feeling effect describes the pleasantly perceived sweetness of sugar, which fills the entire oral cavity and makes lemonades sweetened with sugar appear "full-bodied".
How are steviol glycosides metabolized?
Steviol glycosides are practically not absorbed in the upper gastrointestinal tract and reach the lower intestinal sections unchanged, where they are broken down into steviol by the intestinal flora. A large part of the steviol is absorbed in the large intestine and reaches the liver via the portal vein, the rest is excreted in the stool. In the liver, it is converted to steviol glucuronide, which in humans is mainly excreted in the urine. The steviol derivatives are not stored in the body.
In contrast, household sugar (sucrose) is broken down in the body into glucose and fruit sugar (fructose), which can either be used directly by the organs to generate energy (glucose) or first converted into glucose in the liver (fructose). Sucrose is a carbohydrate and provides 4.1 kcal of energy per gram.
An example of chemically produced sweeteners and their metabolism: aspartame is broken down in the body into phenylalanine, aspartic acid and methanol, which also occur naturally in foods and in the body. The European Food Authority (EFSA) is currently reviewing new study results on aspartame. The reassessment is expected to be completed in May 2013.
Can steviol glycosides also be used for cooking and baking?
Steviol glycosides are available in the form of powdered sweeteners, tabs or as a liquid concentrate. They are heat-stable (up to 180 ° C) and can also be used for foods with a low pH value, such as lemonades and fruit preparations. However, like sugar, they do not have a preservative effect.
When baking, it must also be taken into account that the sweetener has less volume than table sugar. Sponge cake, for example, will not work well with the alternative sweetness. In addition, a licorice-like side note can occur that does not harmonize with all foods. In numerous cookbooks and on the Internet there are tried and tested recipes for using steviol glycosides correctly.
Since the concentration varies from product to product, the dosage should be selected according to the manufacturer's instructions. Especially for people with intolerance such as lactose intolerance and fructose malabsorption, it should be noted that tabs and sweeteners can contain fillers such as lactose (milk sugar) and sorbitol (sugar alcohol) for better dosing.
How safe are steviol glycosides?
The European Food Authority (EFSA) has set the acceptable daily intake (ADI for short) at 4 mg steviol equivalents per kilogram of body weight and day. The ADI value indicates the amount of a substance that a consumer can ingest daily and for life without any health risk. On the basis of various toxicological studies, including laboratory and animal experiments, the substances are checked for their carcinogenic, mutagenic and reproductive properties to determine the ADI value.
4 mg steviol equivalents correspond to approx. 11 mg steviol glycosides. A man weighing 70 kg can consume 770 mg steviol glycosides per day (corresponding to a conversion factor of 1: 300 based on the sweetness of 231 g household sugar).
Steviol glycosides that meet certain purity requirements (according to EU Regulation No. 231/2012) have been approved as sweetener E 960 for use in certain foods (including in flavored beverages, confectionery, dessert dishes, snack snacks, table sweeteners, food supplements) since December 2011. According to the definition, the sweetener must consist of at least 95% steviol glycosides and of this at least 75% of stevioside and / or rebaudioside A (each based on the dry weight). Different maximum usage levels are set for the individual food categories.
How are steviol glycosides made?
To produce the sweetener E 960, the dried and chopped stevia leaves are mixed with water or alcohol. This is how the steviol glycosides are released. Then the dissolved substances are precipitated with salts (separated from the liquid) and decolorized with special resins. This extract is then purified and recrystallized with alcohols. Some of the steps have to be repeated several times until the end product meets the purity requirements.
How should foods sweetened with steviol glycosides be labeled?
The Federal Ministry of Health has published a guideline with lists of terms that state which information on foods containing steviol glycosides can mislead consumers. From 2013, Austria will check whether manufacturers are adhering to this guideline. For example, the label “with steviol glycosides from plant sources” would be correct, while the label “with stevia” would not correspond to the information given.
Where can the stevia plant be grown?
From a climatic point of view, the stevia plant can in principle be cultivated in 120 of the 192 countries in the world, but in countries north of the 45th north latitude - including Austria and Germany - for climatic reasons, not with certain success. Currently, the plant is mainly grown in China. Stevia is currently not grown industrially in Europe, but the plant could be an alternative for regions with tobacco cultivation, which the EU will no longer subsidize in the future.
Why is the stevia plant not approved in the EU?
The EU approval only affects the sweetening compounds and not the living stevia plant, its dried leaves and raw extracts. Here the questions about the harmlessness to health could not yet be answered satisfactorily. Because the stevia plant is a natural product that is composed differently depending on the variety and growing area. In contrast to steviol glycosides, which are extracted using a precise process and whose composition is known, this makes the safety assessment more difficult.
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Mag. Ulrike Keller - nutritionist
Mag. (FH) Silvia Hecher, MSc
European Food Safety Authority (EFSA), Panel on Food Additives and Nutrient Sources Added to Food (ANS): Scientific opinion on the safety of steviol glycosides for the proposed uses as a food additive. EFSA Journal 8 (4): 1537 (2010)
Federal Ministry of Health: Guideline on the non-deceptive labeling of food sweetened with the additive steviol glycosides (E 960). Published with decree BMG 75210/0002-II / B / 13/2012 of June 13, 2012
Benack E, Gerlach S, Joost HG: Stevia - Statement from diabetesDE and VDBD, January 17, 2012
Fitch C, Keim KS, Academy of Nutrition and Dietetics: Position of the Academy of Nutrition and Dietetics: Use of nutritive and non-nutritive sweeteners. J Acad Nutr Diet 2012; 112 (5): 739-758
Wölwer-Rieck U: The leaves of Stevia rebaudiana (Bertoni), their constituents and the analyzes thereof: a review. J Agric Food Chem 2012; 60 (4): 886-895
Kienle U: Which stevia would you like? Cultivation and production - perspectives worldwide. Journal for Consumer Protection and Food Safety 2010; 5: 241-250
Food and Drug Administration: Generally Recognized as Safe (GRAS) Notification for the Use of Stevia Rebaudiana (Bertoni) Bertoni. 2008; www.accessdata.fda.gov/scripts/fcn/gras.../grn_275.pdf (accessed September 2012)
Kienle U: Stevia rebaudiana. Journal Culinaire 2007; 5: 59-69
Association for consumer information: Stevia - sweet fraudulent labeling. Consumer 9/2012
University of Hohenheim; stevia.uni-hohenheim.de/80802.html (Access: September 2012)
German Nutrition Society; www.dge.de/modules.php?name=News&file=article&sid=720 (accessed in September 2012)
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