June 2017 Issue
By Densie Webb, PhD, RD
Vol. 19, No. 6, P. 18
Today's Dietitian reviews the science behind this popular no-calorie sweetener.
Sweeteners with few or no calories provide an alternative to sugar's 15 kcal per teaspoon. These "nonnutritive sweeteners" offer sweetness and, as the term suggests, no nutrition. As a result, they're especially popular among clients and patients with diabetes and those trying to lose weight. Despite inconsistent research findings on their effectiveness for either, they're incredibly popular. Saccharin, aspartame, acesulfame-K, sucralose, and neotame have been available for a while, but stevia is the newest kid on the nonnutritive sweetener block to gain popularity. As a relatively new sweetener, there's little research testing its effectiveness for blood glucose control or weight loss. However, stevia is considered safe and was given GRAS (Generally Recognized as Safe) status in 2008; as such, it doesn't require FDA approval to be used as a food additive.1 In addition, regulatory agencies in more than 65 countries, including the European Union and Canada, have approved stevia for use in foods.2
What Is Stevia?
Stevia is the generic term that refers to different forms of the sweetener, including the whole plant, Stevia rebaudiana Bertoni, which is from the Asteraceae, or sunflower, family.3 For use in foods, however, the term pertains to a high-purity stevia leaf extract that contains at least 95% steviol glycosides. The sweetness is taken from the leaves through a process of extraction, filtration, and dehydration. The plant-based sweetener is 200 to 350 times sweeter than table sugar.4 The purified glycosides used as a sweetener aren't the same as whole stevia leaves, which are sold as a dietary supplement and contain several chemical compounds, not all of which are sweet.5
The antioxidant-rich stevia plant is originally from Paraguay, where, since at least 200 years ago, the leaves have been chewed for their sweet taste, used to sweeten beverages, and used as a medicine.6-8 Beginning in the 1970s, the leaves were employed for the same purposes in Japan.3,4,9 Today, the plant is grown mainly in Paraguay, Kenya, China, and the United States but is also cultivated in Vietnam, Brazil, India, Argentina, and Colombia.3 Because stevia sweetener contains nothing more than a concentrated natural plant compound, albeit highly purified, it's often referred to as a natural sweetener, though the FDA hasn't defined the term "natural."
At least 200 studies have been reviewed by the European Food Safety Authority and the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives that indicate stevia's safety for adults and children, including women who are pregnant or nursing.10 The committee established an Acceptable Daily Intake (ADI) of the sweetener of about 12 mg highly purified stevia extract/kg body weight per day. That's the equivalent of a 150-lb person consuming 40 packets of tabletop stevia sweetener daily.3,10 A recent study done in Belgium looked at the nonnutritive sweetener intake of children with type 1 diabetes, who are considered to be more likely to consume larger amounts of nonnutritive sweeteners, and found it unlikely that they would exceed the ADI for various nonnutritive sweeteners, including stevia.11
The amounts of stevia that products contain aren't listed on labels, and there are no current estimates as to how much stevia typically is consumed in the United States. However, to know if a packaged food contains stevia, look on the ingredient label for stevia leaf extract, stevia, stevia extract, rebaudioside A, Reb A, or steviol glycosides.
The metabolism of steviol glycosides is believed to be similar in animals and humans. Carbohydrate residues (mainly glucose) are attached to the steviol backbone to form the sweet compounds found naturally in the stevia leaf. Steviol glycosides are poorly absorbed in the body and pass through the upper gastrointestinal tract, including the stomach and small intestines, intact. Once they reach the colon, the gut bacteria break them down into steviol by removing their glucose units. Steviol is then absorbed via the portal vein and primarily metabolized by the liver, forming steviol glucuronide, which is excreted in the urine.12 Research has shown that there's no accumulation of stevia (or any byproduct of stevia) in the body during metabolism.13 Its strong sweetening power and poor absorption in the digestive tract contribute to the fact that stevia provides zero calories.14
Stevia and Health
• Weight management: Some, but not all, randomized controlled trials have suggested that substituting foods and beverages sweetened with nonnutritive sweeteners for their regular-calorie version results in modest weight loss.15 There's no reason to believe that substituting stevia for caloric sweeteners would be any better or worse for weight management. One two-year clinical trial found no differences in BMI between those consuming stevia (1,500 mg stevioside powder/day) and those receiving placebo.16 While there's no evidence of caloric compensation when stevia is consumed,17 there haven't been other long-term clinical trials that have looked at the effectiveness of stevia in aiding weight loss.
• Cardiovascular disease: A systematic review and meta-analysis of several clinical trials found a small lowering of blood pressure with supplements of either stevioside or rebaudioside A. As with animal studies, doses were much higher than what would normally be consumed, ranging from about 750 to 1,500 mg per day.18 "The American Heart Association, US Department of Agriculture, US Department of Health and Human Services, and the FDA have all recently put forth recommendations to the American population to curb the amount of added sugars consumed. These efforts highlight the connection between dietary choices and chronic disorders, including cardiovascular disease and obesity," says Carol May, CEO of Wisdom Natural Brands.
• Cancer: Stevia has been determined to be noncarcinogenic. In fact, some laboratory and animal studies suggest that the compounds it contains may act as antioxidants with anticarcinogenic effects.7,19 (The isolated compounds in stevia, but not the sweeteners themselves, have been tested.)
• Dental caries: A recent review of studies concluded that stevia has an antibacterial effect on oral bacterial flora and doesn't contribute to the development of caries.20
• Food allergies: The European Food Safety Authority concluded that there are no known allergies associated with stevia extracts used in foods and beverages.13
• Diabetes: Studies have found no negative effects on blood glucose levels, and stevia has been recognized as safe for people with diabetes, as it produces no glycemic response. Some animal and laboratory studies have suggested that the compounds found in stevia may be beneficial for diabetes. One study on mice found that daily stevioside consumption showed potent therapeutic effects for the prevention and treatment of type 2 diabetes. A small study in patients with type 2 diabetes found that a large dose of stevioside (1 g) given with a test meal improved insulin response by approximately 40% compared with an equal dose of maize starch.21 The researchers suggested that the compound could be the focus for the development of pharmaceuticals.22
• Seizures: A recent study in rats found that S rebaudiana Bertoni in doses of 100 mg/kg of body weight and 200 mg/kg of body weight had anticonvulsive activity. But the doses given were greater than the doses considered safe for humans, and the compound was given intraperitoneally, making it difficult to extrapolate the findings to the effects of much smaller amounts believed to be consumed in the diet. The researchers concluded that the findings suggest that stevia is safe for use in people with epilepsy.23
• Gut microbiome: Studies have suggested that artificial sweeteners such as saccharine and aspartame may affect the balance between "good" and "bad" bacteria in the colon, which could, in theory, have a negative impact on health. A group of researchers in Israel found that the microbial populations that thrived on artificial sweeteners were the same ones shown by other researchers to be in abundance in the guts of genetically obese mice.24 The researchers suggested that artificial sweeteners may directly contribute to enhancing the obesity epidemic that they were intended to fight, via changes in the gut microbiome.25 It's unknown whether stevia may have the same effect in either mice or humans. However, another study found that the growth of the probiotic bacteria Lactobacilllus reuteri was inhibited in the presence of stevioside and rebaudioside A.26 Yet another study found that stevioside and rebaudioside A didn't significantly influence the composition of human fecal bacterial cultures.12
• Other: An older study in male rats found that a daily dose of S rebaudiana Bertoni extract resulted in a decrease in plasma testosterone levels. However, extremely large doses were given. The researchers administered 6.7 g/kg of body weight to the rats, several hundred times the dose considered safe for humans.27
Stevia requires less land, water, and energy to produce the same amount of sweetness found in other natural sweeteners such as cane and beet sugar.3 One of the largest producers of stevia analyzed the carbon and water footprint of the plant and found that, on the basis of sweetening power, stevia resulted in a 64% to 82% reduction in the carbon footprint compared with cane sugar. The water footprint was 92% to 95% lower.3
Stevia is available in powdered and liquid form for use as a sweetener under several brand names, including Born Sweet Zing Organic Stevia Sweetener, SPLENDA Naturals Stevia Sweetener, SweetLeaf Stevia Sweetener, Truvia, Stevia in the Raw, PureVia, and Stevita. It's also found in a growing number of processed foods. Because it can leave a bitter aftertaste when used alone, it's often used in combination with other sweeteners, such as erythritol, aspartame, or table sugar. For example, Coca-Cola has Coca-Cola Life, which uses a combination of stevia and sugar, resulting in 35% fewer calories than regular Coca-Cola. Pepsi has Pepsi True, which uses the same two sweeteners and provides 30% fewer calories than regular Pepsi.
Taste buds on the tongue have many more receptors for bitter tastes than for sweet tastes and, for some, the bitter outweighs the sweet in stevia. "It has a stronger and a more bitter taste than some other sweeteners, and many clients do not like the 'licorice' taste," says Marino Chaparro, MPH, RDN, LD, CDE, a spokesperson for the Academy of Nutrition and Dietetics. But it depends on the food or beverage being sweetened. For example, adding milk to coffee adds viscosity and fat, which helps lessen the bitter taste; a latte, then, might taste better sweetened with stevia than black coffee. For cold beverages, ice cold is best. In addition, sulfur notes like a peach/mango flavor as well as acidic beverages such as lemonade work best with stevia. Research has been underway to identify the sweetest, least bitter compounds in the plant as well as attempt to breed a sweeter stevia plant through selective breeding.28
Stevia is heat stable and can be used in any baked or heated food or beverage. Because stevia is hundreds of times sweeter than sugar, the tabletop sweetener typically contains bulking agents, so for every 1 cup of sugar in a recipe, 1/4 cup or less of powdered stevia should provide the same level of sweetness. According to Priscilla Samuel, PhD, director of the Global Stevia Institute, "While stevia provides sweetness, it lacks some of sugar's other qualities, such as helping to brown foods or adding a tender texture to baked goods." She says that some recipes may require a mix of sugar and stevia or a mix of other caloric or noncaloric sweeteners to attain the desired taste and texture.
Since 2008, more than 10,000 stevia-containing products were launched worldwide. In 2016, 563 stevia-containing products were introduced in North America alone, representing a 34% growth over 2015.
"As a certified diabetes educator, I see many clients who use stevia among other nonnutritive sweeteners as a part of their daily diet," Chaparro says. She adds, "As someone who specializes in children with diabetes, I believe that kids with type 1 diabetes can benefit from including nonnutritive sweeteners in their diets. They can still enjoy a sweet treat without significantly affecting blood sugar, and it helps them to feel normal. That's important for these children." Stevia leaf extract, used as a sweetener and consumed in amounts below the ADI of 12 mg highly purified extract/kg body weight has been deemed safe by the FDA as well as agencies in many other countries including the European Union and Canada. Some preliminary studies even have suggested beneficial effects on blood glucose control and cardiovascular disease risk factors, but doses tested often were many times greater than what currently has been deemed safe.
Stevia is still a relatively new addition to the nonnutritive sweetener market, and more research is needed before it can be known for sure what the long-term effects may be—beneficial or not. But, based on what's known right now, stevia sweetener is considered a safe choice for anyone trying to curb his or her sugar intake.
— Densie Webb, PhD, RD, is a freelance writer, editor, and consultant based in Austin, Texas.
SAMPLING OF PRODUCTS CONTAINING STEVIA
Chobani's Simply 100 Greek Yogurt
Dannon Oikos Triple Zero Greek Nonfat Yogurt
LALA Go Bananas Smoothie
Monster University Flavor Water
Mott's Fruit Punch Rush
Silk Light Soymilk
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22. Philippaert K, Pironet A, Mesuere M, et al. Steviol glycosides enhance pancreatic beta-cell function and taste sensation by potentiation of TRPM5 channel activity. Nat Commun. 2017;8:14733.
23. Uyanikgil Y, Cavusoglu T, Balcioglu HA, et al. Rebaudioside A inhibits pentylenetetrazol-induced convulsions in rats. Kaohsiung J Med Sci. 2016;32(9):446-451.
24. Shell ER. Artificial sweeteners may change our gut bacteria in dangerous ways. Scientific American. April 1, 2015. https://www.scientificamerican.com/article/artificial-sweeteners-may-change-our-gut-bacteria-in-dangerous-ways/. Accessed April 27, 2017.
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27. Melis MS. Effects of chronic administration of Stevia rebaudiana on fertility in rats. J Ethnopharmacol. 1999;67(2):157-161.
28. Jennings K. Here's what the stevia sweetener really is — and why some people think it tastes bad. Business Insider website. http://www.businessinsider.com/what-is-stevia-why-does-it-taste-bad-2014-7. Published July 3, 2014. Accessed April 27, 2017.