The shrub Stevia rebaudiana Bertoni, commonly known as Stevia, was first mentioned by the Spanish physician and botanist Pedro Jaime Esteve (1500-1556) who found it in the northeast of the territory now called Paraguay.
The Guaraní Indians of this area, as in the south of Brazil, have been using “ka’a he’ê” (“sweet leaf”), as it is called in Guaraní, for hundreds of years as a sweetener in yerba mate, and several Tribes reported the use of this plant in the control of fertility in women, applying concentrated infusions of Stevia for prolonged periods.
It is precisely this contraceptive property that has been discussed from the 1970s to the present in the scientific literature. The reason is simple: Who wants to consume a sweetener that suddenly makes you sterile?
The stevia leaf contains a complex mixture of glycosides (compounds in which one or more sugar molecules are attached to a carbohydrate with no moiety). These compounds give the leaves an intensely sweet flavor, some 30-45 times sweeter than sucrose, the sweetness of refined sugar. To date, ten different chemical compounds (chemically, all steviol glycosides) responsible for the sweet taste of the plant have been isolated: stevioside, rebaudioside A, B, C, D, E and F, dulcoside A, rubusoside and steviolbioside. The highest concentration of sweetening effect comes from stevioside and rebaudioside A, responsible for Stevia extract being 250-300 times sweeter than sucrose with almost zero calories (about 0.2 calories per gram).
Both sweet steviol glycosides are chemically diterpenic glycosides, substances composed of two molecules of different types of sugar and a molecule called steviol. Steviol serves as the “backbone” of the chemical structure and is structurally similar to the plant hormones gibberellin and kaurene. Several studies show that these glycosides are, at least partially, metabolized in the body, releasing sugar molecules and steviol.
Is it safe to use Stevia instead of sugar?
It is precisely this steviol compound that has drawn the attention of toxicologists for many years. In studies with bacteria and cell cultures, it was shown that this compound is genotoxic (that is, it is capable of changing genetic information). However, more recent studies with mice, rats, and hamsters indicated that relatively high concentrations of steviol are required to cause significant damage to DNA, the molecule of life that contains all of our genetic information.
Browsing toxicology databases, there are hundreds of publications discussing possible adverse health effects of stevia extract, but the results are not very consistent. In particular, the effects on fertility and the potential carcinogenicity of steviosides have been the subject of controversy in the scientific world. It was a study published in 1968 by Professor Joseph Kuc Purdue of the University of Indiana, USA, which started a controversial discussion about stevia and fertility. Teacher. Kuc detected a clear contraceptive effect in female rats given high doses of stevia. The fertility rates of the rats were reduced by as much as 79 percent.
Although the result of this study was not confirmed by other scientific groups, a study published in 1999 by Prof. Melis of the University of Sao Paulo also reported a reduction in the number of sperm in male rats after applying high doses of glycosides of Stevia. Carcinogenicity or mutagenicity concerns were not confirmed in the vast majority of toxicology studies.
Although the adverse health effects of Stevia have never been directly tested in humans, authorities in the United States, Canada, and the European Union have deemed Stevia extracts to be unsafe in application as a tabletop sweetener due to the lack of long-term toxicology. studies. Instead, authorities from other countries such as Japan, China, Australia, New Zealand, Brazil and Mexico have a different point of view and accept the use of Stevia extracts as a natural sweetener. In several other countries, particularly in Latin America and Asia, Stevia and its extracts are available with an unverified regulatory status. In Japan, Stevia extracts have been commercially available since 1971 as a tabletop sweetener and there are no reports of health problems associated with this product.
In the US, the Food and Drug Administration (FDA) has approved the use of Stevia extracts as a “nutritional supplement”, but not as a tabletop sweetener. Only the glycoside Rebaudioside A in its pure form is considered a “Generally Recognized Safe Substance” (GRAS), since December 2008. In contrast, Stevioside, the other main compound of Stevia extracts, was not recognized as GRAS by the FDA.
In both Canada and the European Union (EU), Stevia was banned from use as a tabletop sweetener due to insufficient evidence to prove its safety. But now this situation is likely to change. In April 2010, the European Food Safety Authority (EFSA) carried out a new evaluation of the available toxicological information. As a result of this review, stevioside and stevia extracts are now generally considered safe when used as tabletop sweeteners, at least under certain conditions.
EFSA established an Acceptable Daily Intake (ADI) of 4 mg per kilogram of body weight for steviosides, the same ADI recommended by the World Health Organization based on a WHO document published in 2008. In layman’s terms, a 70-year-old adult kg can consume 280 mg of Stevia extract every day without running any health risk. Since Stevia extract is about 250 times sweeter than table sugar, an adult can replace 70 grams of refined sugar daily with Stevia extract. This is equivalent to about 4-5 tablespoons or about 20 teaspoons of sugar. As children have a lower body weight, the dose should be reduced in proportion to their weight.
It is interesting to compare these data with Aspartame, the most widely used synthetic tabletop sweetener worldwide. Food safety authorities around the world have established Acceptable Daily Intake (ADI) values for aspartame at 40 mg/kg body weight based on a recommendation from the 1980 FAO/WHO Joint Expert Committee on Food Additives. of the United Nations Food and Agriculture Organization). This means that, based strictly on the available toxicological data, stevia is considered about 10 times more “toxic” than aspartame.
Although Stevia sweetener is an isolated product of a plant and not the product of a classical chemical process, it never hurts to be critical, because “natural” does not necessarily mean risk-free. As a conclusion, Stevia extracts can be considered safe if not consumed in large quantities. The common belief that this “natural” product is safer than other commercially available tabletop sweeteners is not supported by available toxicological data.