Something to sweeten up all our future lives
The Irish Times
Health Supplement, p. 13
14 April 2009
DOES IT WORK? The use of stevia as a natural sweetener
ARE YOU READY for herbal Coke and Pepsi? At the end of last year, the US Food and Drug Administration approved the use of a natural sweetener called stevia. Several major food and drink producers are reportedly ready to start using it, although it is not yet approved in Europe. Ironically, one of the concerns slowing the herb’s approval has been its use in traditional medicine.
Stevia is a shrub that is native to the highlands of Paraguay and Brazil. Efforts are being made to cultivate it around the world, although South America and China are still the leading producers. The sweeteners are available as both dried plant material and liquid extracts which are 10 to 15 times sweeter than sugar.
The sweetness of stevia comes from a group of compounds called glycosides. These are made in the plant when molecules of glucose (a form of sugar) are attached to another compound called steviol. The most abundant glycoside in stevia is called stevioside which makes up 10 per cent of the dried plant material. Stevioside is about 300 times more sweet than sugar, and several other glycosides in stevia are also very sweet.
Stevia has also been used for centuries in South American traditional medicine as a treatment for diabetes and to reduce blood pressure.
Evidence from studies
Because of its use as a sweetener in various countries, a large number of laboratory studies have been conducted. When animals are first given stevioside, most of it passes through their bodies unchanged. Over time, some of it is broken down to release steviol and glucose. Steviol appears to be the compound that may influence blood pressure and diabetes. In animal and laboratory studies it has been found to have several actions.
A small number of studies have been conducted with stevioside as a treatment for diabetes. One small study with diabetic patients compared their blood sugar level after eating a meal containing stevioside compared to the same meal containing starch. The blood sugar level was significantly lower after stevioside, which is beneficial with diabetes. However, a more recent study examined the effects of taking stevioside for three months. It found no differences in blood glucose levels in diabetic patients compared to those who took a placebo.
The same study also measured people’s blood pressure and found that three months taking stevioside produced no changes. This contrasts with an earlier study in China which followed people with slightly raised blood pressure for two years. Blood pressure levels were reduced by about 10mm of mercury in those taking stevioside compared to those taking a placebo. Similar results were found in another study which had been conducted for three months.
Overall, this is insufficient human research to base any recommendations upon.
A large number of toxicity studies have been conducted on stevia, especially in Japan where it has been approved as a sweetener for about 30 years. These have concluded that stevia is safe when taken in daily amounts of up to 5mg per kilogram body weight. Clinical trials have usually given people more than this, up to 1 g per day. Adverse effects have not been reported in these studies. However, some people have reported intestinal discomfort after using stevia.
Given the growing incidence of obesity, stevia looks like it may play an important role as a natural sweetener. While being very sweet, it has the added advantage of providing no calories because almost all the material passes through the digestive tract unchanged. The molecule is also stable in acid and heat which means it can be used safely in cooking.
The role of stevia or stevioside in treating diabetes or high blood pressure is more unclear. These conditions require attention to several lifestyle factors, and effective conventional medicines are available if necessary.
If stevia is shown to have a relatively small effect on blood glucose or blood pressure, this could be an added benefit to its role as a sweetener. Ironically, if stevia is shown to have a larger effect, this could be a concern if it is widely used in foods and drinks. The European Food Safety Authority is reviewing an application for approval.
Globally, the use of stevia as a natural sweetener is likely to increase in the near future, especially if Coke and Pepsi put it in their products.