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Stevia

MagazineDecember 2010 (Vol. 21 Issue 9)Stevia

For those of us who have a sweet tooth, stevia sounds like the perfect alternative to sugar and artificial sweeteners such as aspartame

For those of us who have a sweet tooth, stevia sounds like the perfect alternative to sugar and artificial sweeteners such as aspartame. It's natural (derived from a small perennial South American shrub), up to 300 times sweeter than table sugar and completely calorie-free. It might even be good for us, with reported benefits that include lowering both high blood pressure and high blood sugar levels, while boosting the immune system and reducing inflammation.

Nevertheless, there have been safety concerns surrounding stevia and, in some countries, including the UK, the herbal sweetener is either restricted or banned. So what's the real story on stevia?

Sweet benefits

Stevia is the common name for the sweet-tasting extracts isolated and purified from the leaves of Stevia rebaudiana, a South American plant that has been used since ancient times as both a sweetener and a medicine.

Although the word 'stevia' may also be used to refer to the entire plant, it is these extracts-also known as 'steviol glycosides'-that are sold in healthfood shops and online under the name 'stevia'. Also, these extracts are now increasingly being used as sugar substitutes in various foods and drinks.

Stevioside and rebaudioside A are the most commonly used steviol glycosides, and both have been the subject of scientific study. Although consumers tend to prefer the sweeter taste of rebaudioside A (Chem Senses, 2010; 35: 433-43), it is stevioside that has been associated with various health benefits.

Most recently, US researchers tested the effects of stevioside-along with aspartame and sucrose (ordinary table sugar)-on food intake and satiety in both healthy and obese individuals. Participants were given a pre-meal containing either stevioside (290 calories), aspartame (290 calories) or sucrose (493 calories) before lunch and dinner, after which their total food intake, and feelings of hunger and satiety, were measured.
The researchers found that, despite consuming significantly fewer calories when given stevioside- or aspartame-sweetened pre-meals (compared with sucrose), the participants did not compensate by eating more at either their lunch or dinner, but reported similar levels of satiety under all three conditions.

This suggests that the use of sugar substitutes in the diet might be a useful way to manage food intake. The most interesting finding, how-ever, was that only stevioside reduced both blood glucose and insulin levels after eating, indicating that the herbal sweetener may be beneficial for diabetics (Appetite, 2010; 55: 37-43).

Indeed, extracts of S. rebaudiana have long been used in the treatment of diabetes in South America (Pharmacol Ther, 2009; 121: 41-54), and several studies have found stevioside to have a positive effect on glucose metabolism.

In a trial of 12 patients with type 2 diabetes, a standard test meal supplemented with 1 g of stevioside (with 1 g of starch used as the control) was able to reduce post-meal blood glucose levels by around 18 per cent. "Stevioside may be advantageous in the treatment of type 2 diabetes," the researchers concluded (Metabolism, 2004; 53: 73-6).
Another study-albeit in rats, so it may not apply to humans-showed that stevioside has a number of antidiabetic effects, including stimulating insulin and reducing blood glucose levels (Phytomedicine, 2002; 9: 9-14).

Stevioside also appears to have an impact on the cardiovascular system. After a number of animal studies demonstrated that stevioside had an antihypertensive (blood-pressure-lowering) effect, researchers in Taiwan decided to test the sweetener on patients with high blood pressure.

A total of 106 men and women, aged 28 to 75 years, were given capsules containing stevioside (250 mg) or a placebo three times a day-an amount similar to what would be used as a sweetener-and were followed-up at monthly intervals for one year. After three months, both systolic and diastolic blood pressure in the stevioside group had decreased significantly, an effect that persisted throughout the entire year-with no adverse effects (Br J Clin Pharmacol, 2000; 50: 215-20).

Another study-this time using a stevioside dose of 500 mg three times a day for two years-found that stevioside not only reduced blood pressure in those with mild hypertension, but also improved their quality of life as assessed by a standardized questionnaire (Clin Ther, 2003; 25: 2797-808).

In contrast, however, one team of researchers recently reported that stevioside (250 mg, taken three times a day for three months) had no blood pressure or glucose effects in type 1 and 2 diabetic patients or in non-diabetics with normal-to-low blood pressure (Regul Toxicol Pharmacol, 2008; 51: 37-41).

This suggests that stevioside might only be able to lower blood glucose and blood pressure when they are abnormally high (Pharmacol Ther, 2009; 121: 41-54), although this still doesn't explain the lack of effect in the diabetics in the study.

As for rebaudioside A, a 16-week study reported that, when regularly used at a dose of 1000 mg/day, it failed to reduce either glucose or blood pressure levels in patients with type 2 diabetes (Food Chem Toxicol, 2008; 46 Suppl 7: S47-53).

Although one test-tube study using mouse pancreatic islet cells has suggested that the glycoside may have a potential role as a treatment for type 2 diabetes (Metabolism, 2004; 53: 1378-81), another study using a type 2 diabetes rat model-which had shown benefits with stevioside-found that rebaudioside A had no beneficial effects whatsoever on these animals (Rev Diabet Stud, 2005; 2: 84-91).

As well as being potentially useful for people with diabetes and high blood pressure, stevioside has also exhibited anti-inflammatory, anti-cancer and immunomodulatory (immune-system-regulating) actions (Pharmacol Ther, 2009; 121: 41-54). In addition, neither stevioside nor rebaudioside A appear to be cario-genic (causing tooth cavities)-unlike sugar (Caries Res, 1992; 26: 363-6). However, as this evidence has come only from animal or test-tube studies, we don't yet know whether the results would apply to people.

Stevia safety

Regardless of whether or not stevia has health benefits, the key issue is whether this natural sweetener is safe to use as a calorie-free alternative to sugar. Indeed, the health concerns over artificial sweeteners such as aspartame and saccharin-in particular, their reported link with cancer-has no doubt led many to believe that sugar is probably the lesser evil. So the question remains: Is stevia truly a better option?

Interestingly, even though it's natural, there have been concerns over the safety of stevia, which is why it is restricted or banned in certain countries. The main fears-based on early animal studies concerning a metabolite of stevia-are that it could cause cancer, damage DNA and interfere with fertility. Yet, numerous scientific reviews have found it to be safe. One US "critical review" reported that neither stevioside nor its derivatives "pose a risk of genetic damage following human consump-tion" (Food Chem Toxicol, 2008; 46 Suppl 7: S83-91). Another review concluded that stevioside has "very low toxicity", and that it is "safe when used as a sweetener" (Phytochemistry, 2003; 64: 913-21). Similarly, rebaudioside A appears to be non-toxic, even at high levels of dietary intake (Food Chem Toxicol, 2008; 46 Suppl 7: S1-S10; Int J Toxicol, 2008; 27: 65-80).

Nevertheless, we still don't know the precise effects-if any-of stevia consumption over the long term, although clinical trials have so far reported no adverse events other than some minor side-effects (such as nausea and dizziness). Indeed, some claim that the fact that stevia has been used in Japan and other countries for decades, with no reports of significant adverse effects, is a testament to its long-term safety in humans (Br J Clin Pharmacol, 2000; 50: 215-20).

Perhaps due to the growing evidence of stevia's safety-or perhaps due to pressure from companies such as Coca-Cola and PepsiCo, both of which have recently launched their own stevia-based sweeteners-the regulatory authorities in both the US and Europe have begun to warm to stevia. As of December 2008, rebaudioside A has been generally recognized as safe (GRAS) by the US Food and Drug Administration (FDA). However, the leaves and other extracts of the stevia plant are only available as dietary supplements.

In the EU, stevia is currently banned as a food and drink sweetener, although you can still find it online and in healthfood shops described as a herbal supplement, cosmetics additive or other non-sweetener product. In 1984, 1989 and 1999, the Scientific Committee for Food (SCF) evaluated the use of stevioside as a sweetener, but concluded that it was "toxicologically not acceptable" due to insufficient available data to assess its safety.

Yet, according to the latest Scientific Opinion from the European Food Safety Authority (EFSA), recent toxicological tests have shown that "steviol glycosides are not genotoxic, carcinogenic, nor associated with any reproductive/developmental toxicity" (see www.efsa.europa.eu/ en/scdocs/scdoc/1537.htm).

The European Commission is now expected to give the green light for certain stevia extracts to be used in foods and drinks in EU member states early next year. In France, highly purified (97-per-cent) rebaudioside A has been approved since September 2009, after the country successfully applied for a two-year window to use it in advance of the anticipated EU-wide go-ahead.

So, it looks as if we're going to be seeing a lot more of stevia-and, considering its potential for diabetics and favourable safety profile compared with the likes of aspartame and other artificial sweeteners, this can only be a good thing.

Joanna Evans

WDDTY VOL. 21 ISSUE 08


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