|The stevia plant (Stevia rebaudiana)|
Long before the media frenzy over stevia, there were concerns being raised about saccharin and aspartame, two of the most popular artificial sweeteners which infiltrated our foods whether we knew it or not. Health concerns of aspartame are many and varied from adverse reactions such as headaches, muscle spasms and anxiety to exacerbating existing conditions such as MS, diabetes and Alzheimer's Disease. Saccharin on the other hand has had a long and chequered history over its alleged carcinogenic (cancer-causing) properties. Little wonder then that stevia is proving very popular.
History &Traditional Use
Stevia is a genus that encompasses over 240 species. It is in the sunflower family (Asteraceae) and is native to subtropical and tropical regions from western North America to South America including central America and Mexico. The species of great interest to the food industry is Stevia rebaudiana (common name sweetleaf or sugar leaf). Human use of sweetleaf originated in South America and has enjoyed a long history of use in both food and medicine. The Guarani people of Paraguay and Brazil have been using stevia for more than 1500 years. In its whole, unprocessed form, stevia leaves have 30-45 times the sweetness of refined sugar (sucrose). The leaves can in fact be eaten fresh or cut leaves can be used in beverages and foods to sweeten them.
The traditional method of use by Paraguayan Guarani Indians was to dry the leaves and use this form to sweeten tea, herbal teas particularly yerbe mate and traditional medicines. Dried and fresh leaves are also chewed as a 'sweet treat'. Stevia was regularly used in drinks many times a day with no side-effects. The use of dried leaves (pieces or powdered) is unacceptable in domestic cooking because it can leave a sediment, it can cause frothing and discolour the food green which can make it distinctly unappealing and unappetising!
It's medicinal attributes was as a cardiac stimulant, its anti-obesity effects, a hypotensive, relief of heartburn and lowering of uric acids levels therefore good for gout. There is much interest in the scientific community to investigate some of these traditional uses to determine potential and new drug treatments.
Plant constituents and AC
The active constituents that confer sweetness to stevia are collectively referred to as steviol glycosides: stevioside, rebaudiosides A, D and E, dulcosides A and B. However, only two of these have attracted attention regarding the food industry: stevioside and rabaudioside A.
Stevioside is a non-carbohydrate glycoside compound. Therefore, it lacks the properties that sucrose and other carbohydrates have. Rebaudioside A has the least bitterness of all the steviol glycosides in the stevia plant. To produce rebaudioside A commercially, stevia plants are dried and subjected to a water extraction process. This crude extract contains about 50% rebaudioside A; its various glycoside molecules are separated via crystallization techniques, typically using ethanol or methanol as solvent. This allows the manufacturer to isolate pure rebaudioside A.
Stevia extracts have several unique properties such as long shelf-life, high temperature tolerance, it's non-fermentative and contains near zero calories. Stevia extracts, like rebaudioside A are found to be 300 times sweeter than sucrose (table sugar) and it is this which is much sought after. Many have found stevia to have a bitter aftertaste; this may be attributed to the presence of sesquiterpene lactones, essential oils, tannins and flavonoids but stevioside and rebaudioside A also contribute to this. Of all the steviol glycosides, it is rebaudioside A that is the sweetest and most stable, and it is less bitter than stevioside.
Other important constituents:
- antioxidants (triterpenes, flavonoids, tannins)
- chlorogenic acid
It is very difficult to get hold of the raw, unprocessed version of stevia - it is usually sold in a powdered or liquid extract form. Safety studies therefore have to include these versions rather than focussing on the whole plant. Various reports in animals and humans indicate that the safety of stevia is not yet determined. Although stevia has been used without any problems for many years in its native Paraguay and in other countries for a lesser time, health and safety issues have been receiving considerable attention in the past 20 years. There has been much media attention in the US, including claims and counterclaims before the FDA. Many of these claims relate to its potential competitive market position in relation to aspartame.
Global use and legislation
Stevia products including rebaudioside A have been approved for use in the US since 2008 as nutritional supplements and as purified extracts when it was granted GRAS status ie. Generally Recognised As Safe. Interestingly however, whole leaf or crude stevia extracts do not have approval to be used as food additives. This is because in the US, health supplements do not need to prove that they are safe (unbelievable!) but food additives do. This decision was essentially based on toxicology reports which demonstrated genotoxicity and mutagenicity (ie. can cause genetic mutations) from stevia extracts. However, lab studies use doses that are extremely high and in reality, stevia is not consumed at these extremely high doses. Many critics argue that this sends out a contradictory message and have been campaigning for stevia to be added to the food additive list. In Europe, it's a different picture - the European Food Standards Agency (EFSA) approved stevia and its extracts as food additives in 2011. It has been authorised for widespread introduction. Japan banned artificial sweeteners about 40 years ago and have been using the processed form of stevia since then. Stevia (in its whole form or as extracts) have been approved by various countries across the world.
Medicinal benefits and health risks
The medicinal benefits of stevia in the modern world is yet to be determined. However, much can be gleaned from traditional practices and the conditions being considered. Current research has evaluated stevia's effects on obesity and hypertension. Other studies have shown that there is negligible effect on blood glucose, and may even enhance glucose tolerance. However, for diabetics and others on a low-carbohydrate diet, stevia is a very useful alternative to sugar. Additionally, stevia possesses anti-fungal and anti-bacterial properties therefore it can be safely used in herbal medicines, tonics for diabetic patients and also in daily use as mouthwashes and toothpastes. Stevia leaf tea also offers excellent relief for an upset stomach.
The Japanese have performed over 40,000 clinical trials on stevia and found it to be safe although there is no reliable data which determines safe doses. Stevia is generally well tolerated and is safe to use in pregnancy. It is also safe for diabetics and no allergic reactions seem to exist for it. However, those with allergies to plants in the Asteraceae family (and this includes ragweed, chrysanthemums, marigolds, daisies, sunflowers etc..) are advised not to use it. As with most things, individuals react differently to the same product.
A question of taste?
Stevia in its raw form, although incredibly sweet, has a very subtle liquorice taste to it. A sign of an excellent stevia product is one that is free of this liquorice essence and still not bitter (many call this an aftertaste). Given that the whole form of the leaf is incredibly difficult to get hold of, it is perfectly legal to grow stevia plant yourself (well in the UK at least!). The leaves can either be eaten whole, dried then added to food or boiled, cooled and strained (filtered) to control the level of sweetening that is required. The latter method may be preferable in some situations such as in diabetics and those wanting to reduce their craving for sweet foods as well as fatty foods in a measured, gradual way.
Some people have simply developed an insatiable need for sweet foods and instead of altering the palate to modify their idea of what 'sweet' is, have resorted to sugar alternatives. Resetting the sweet sensors requires effort and perhaps an approach that people are too lazy to adopt. Many of the stevia products on the market are highly processed and contain other substances as the most abundant substance in stevia:
- eg. erythritol - is a naturally occurring sugar that is sometimes found in fruit, but food manufacturers don’t actually use the natural version. Instead they start with genetically engineered corn and then go through a complex fermentation process to come up with chemically pure erythritol
- eg. xylitol - is a sugar alcohol that is not fully digested. Although naturally-occurring in beets, mushrooms, oats, berries and corn, and commercially produced from birch trees, it is not known whether commercial stevia with this ingredient is from a natural source
- eg. dextrose - is a sweetener that’s also derived from genetically engineered corn and has a long complicated manufacturing process, just like erythritol
- eg. natural flavours - manufactured and not natural at all. This makes it difficult to stop eating or drinking because the flavours they have synthesized will trick your mind into wanting more
- eg. agarve inulin - even certified organic stevia can have sneaky ingredients added which has more organic agave inulin than the stevia extract itself. Agave inulin is a highly processed fibre derivative from the blue agave plant, quite different to the healthier, pure agave syrup
- eg. silica - used in the construction industry, this substance can irritate the gut
|A commercial product widely |
available in supermarkets. Made by
Coco-Cola and Cargill
- raw sugar (not brown sugar!)
- sugar cane (but this is not feasible unless you live in the fields where it is harvested!), or near a place that sells them
- honey (one of the most natural sugars produced by bees and used for centuries)
- jaggery (a traditional sugar consumed in Asia and Africa made from the products of both sugar cane and the date or coconut palm tree. Can be found in specialist stores in the UK
- agave syrup or nectar (a natural product used widely in Mexico and S. America, it is made from the Agave spp and resembles honey although it is sweeter and less viscous
|A natural sugar product made from |
the Agave plant
|A commercial stevia product made |
by the PepsiCo and Whole Earth
|Jaggery pieces - a natural sugar product made |
from sugar cane, date palm and/or coconut palm
|Probably the only stevia product |
that is made from the whole leaf
- There are many commercial websites providing information about stevia but this is not always objective or entirely reliable! A good scientific review (Goyal & Goyal, 2010) provides a comprehensive account for stevia. You can download it here: http://wateryouwatingfor.files.wordpress.com/2011/04/stevia.pdf
- A full toxicological review of rebaudioside A was conducted by Kobylewski & Eckhert for The University of California. You can download it here: http://www.cspinet.org/new/pdf/stevia-report_final-8-14-08.pdf