Stevia Kills Good Gut Bacteria - One Study Enough to Stop Using the Natural Sweetener? Probably Not in View of its Anti-Diabetes, Anti-LDL, Anti-Viral & Anti-Cancer Effects

Study indicates stevia kills healthy gut bacteria. So, how bad is it? Are the effects significant, will they have an impact on your overall health and does this mean you must not use stevia any longer?
A recent study from the Institute of Microbiology and Biotechnology at the University of Latvia in Riga shows the impossible: Stevia, the "natural" sweetener that's everybody's darling, could mess up your gut microbiome by killing large numbers of the beneficial Lactobacillus Reuteri bacteria in your tummy - exactly those bacteria of which several studies have shown that supplementing will help cure acute diarrhea in young children (Shornikova. 1997), is capable of reducing frequency and intensity of antibiotic-associated side-effects during eradication therapy for H. pylori. (Lionetti. 2006), confers broad-spectrum protection against disease in humans and animals (Casas. 2000), has cholesterol lowering effects (Jones. 2012) and much much more.
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In view of the fact that it would appear as id Lactobacillus reuteri was clearly one of the "good guys" it seems that the results I. Denin a, P. Semjonovs, A. Fomina, R. Treimane and R. Linde report on their latest study in Letters in Applied Microbiology (Denin. 2014) were really bad news:
Figure 1: Influence of stevioside (a) and rebaudioside A (b) on biomass formation in Lactobacillus reuteri strains (24 h | Denin. 2014).
"In samples supplemented with stevia glycosides, the growth of all Lact. reuteri strains was slightly inhibited – however, a statistically significant concentration-dependent inhibitory effect was not observed for all strains (Fig. 1).

Comparing both the glycosides, the inhibitory effect of stevioside was more pronounced for strains 44 and 16, while the effect of rebaudioside A was more pronounced for strains 16 and 19. Statistically significant concentration-dependent inhib itory effect was observed for lactic acid and acetic acid synthesis. The decrease in lactic acid and acetic acid production was observed for both stevioside and rebaudioside A. [...] Although the inhibitory effect of stevioside on pH was observed at different stevioside concentrations, the effect was evident for all strains. Rebaudioside A had a more pronounced inhibitory effect on pH values of certain strains including Lact. reuteri 12, 16, 43 and 44" (Denin. 2014 | my emphasis).
The good news, however, is in the details: The inhibitory effect was "slight" (see quotation above) and the design of the study leaves it open, whether similar effects would occur in vivo and thus outside of a glycoside, stevioside and rebaudioside laden Petri dish.
Previous studies seem to refute significant effects of stevia on the human microbiome! In 2003, Gardana et al. found no effect of stevia on the make-up of human fecal cultures when they were incubated with either stevioside or rebaudioside A. Only the fact that bacteroides, i.e. the "enemies" of lactobacilli, were the most efficient in hydrolyzing Stevia sweeteners to steviol would suggest that there may be an overall effect on the human microbiome form stevia (ab-)use.
And while we have little in vivo evidence that stevia is bad for you, a brief review of the contemporary scientific literature on Stevia yields the following "proven" (mostly only in a handful, if not just a single study) benefits:
  • Stevia has been implicated in diabetes and hyperlipidemia treatment and its effects on blood glucose levels are not a mere result of the corresponding reduction in sugar intake.
    Figure 2: Effects of stevia vs. diabetes drug Glibenclamide on blood glucose and lipid levels in diabetic rodents; data expressed relative to healthy control (Singh. 2014)
    In a recent rodent study that compared the effects of stevia against those of the often-prescribed diabetes-drug Glibenclamide, the natural sweetener outperformed the drug in many in its ability to reduce LDL and blood sugar and was not far off of what the Glibencamide did for the diabetic lab animals in terms of its effects on HDL and VLDL (see Figure 2).

    Previous human studies indicate that stevia extracts will also increase the increased 16 healthy human volunteers whose plasma glucose levels during an oral glucose tolerance tests were significantly lower after having consumed 5 grams of aqueous leave extract at regular 6-h intervals for 3 days (Curi. 1985).
    Figure 3: Effects of stevia and aspartame replacement of sucrose in test meals that were fed to obese and normal-weight volunteers on postprandial blood glucose levels (Anton. 2010)
    Moreover, in a more recent study by Anton et al. where stevia was compared to aspartame, it had the same beneficial effects on total energy intake and let to statistically significant reductions in postprandial glucose levels of both obese and lean study subjects (see Figure 3) that did not reach significance when the sucrose content of the test meal was replaced by aspartame.
  • In-vitro stevia appears to have anti-cancer effects, as well. That's at least what studies by  Jayaraman et al. (2008) observed with stevia extracts. An effect that may be related to both it's anti-microbial, as well as its potent anti-oxidant activity (Tadhani. 2007) of the whole leaves and leave extracts of which Tahani et al. found that they contain significant effects of folic acid (52.18 mg/100 g) and vitamin C, as well as 130.76 μg catechin and 15.64 μg quercetin for leaves and 43.99 μg catechin and 1.57 μg quercetin for cellus at mg of water extracts, respectively.

    Furthermore, Tadhani et al.'s results showed that the leaf extracts contained higher amounts of free radicals, hydroxyl radicals and superoxide anion radical scavenging activities than those of the callus extracts or the anti-mutagenic effects Cariño-Cortés et al. report in their 2007 study. Whether anything similar can be observed with the white "stevia" powder that is used by most people to sweeten their foods is yet questionable - it's after all pure steviosid and thus devoid of all of the previously mentioned compounds.
    Figure 1: Several natural constituents of the stevia plant, including steviosides, which are the naturally sweet agents in stevia have potent anti-viral activity against Epstein-Barr virus; values in brackets
    represent % of untreated control dish (Konoshima. 2002)
    Another possible anti-cancer mechanism may be related to stevia's ability to kill viruses like the Epstein-Barr virus that has been implicated in the pathogenesis of Burkitt’s lymphoma, Hodgkin’s disease, non-Hodgkin’s lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised humans (Thompson. 2014).
Against that background it seems questionable that the new evidence of negative effects on allegedly healthy gut bacteria (just want to remind everyone that we have no clue what the optimal gut microbiome would look like) is significant enough to have us all reconsider our use of tiny amounts of stevia as a sweetener in our foods.
Read more about the effects artificial sweeteners have on the microbiome in a prevoius article | go ahead!
Interim conclusion: While I am not all too scared that stevia will mess with my gut microbiome in a way that makes me sick, fat and what not, I truly believe that the effects of artificial sweeteners on the make-up and density of the human gut microbiome is still massively under-researched - and that in spite of the fact that it could have a significant effect on the health of us all.

As s SuppVersity reader you will also be aware that this is not a stevia-specific effects. Only recently I have written about similar effects for a bunch of artificial sweeteners - an article I can only recommend to anyone who hasn't read it yet | Comment on Facebook.
  • Anton, Stephen D., et al. "Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels." Appetite 55.1 (2010): 37-43.
  • Casas, Ivan A., and Walter J. Dobrogosz. "Validation of the probiotic concept: Lactobacillus reuteri confers broad-spectrum protection against disease in humans and animals." Microbial ecology in health and disease 12.4 (2000): 247-285. 
  • Curi, R., et al. "Effect of Stevia rebaudiana on glucose tolerance in normal adult humans." Brazilian journal of medical and biological research= Revista brasileira de pesquisas médicas e biológicas/Sociedade Brasileira de Biofísica 19.6 (1985): 771-774.
  • Deniņa, Ilze, et al. "The influence of stevia glycosides on the growth of Lactobacillus reuteri strains." Letters in applied microbiology 58.3 (2014): 278-284. 
  • Gardana, Claudio, et al. "Metabolism of stevioside and rebaudioside A from Stevia rebaudiana extracts by human microflora." Journal of agricultural and food chemistry 51.22 (2003): 6618-6622. 
  • Jayaraman, Sathishkumar, Muthu Saravanan Manoharan, and Seethalakshmi Illanchezian. "In-vitro antimicrobial and antitumor activities of Stevia rebaudiana (Asteraceae) leaf extracts." Tropical Journal of Pharmaceutical Research 7.4 (2008): 1143-1149.
  • Jones, M. L., C. J. Martoni, and S. Prakash. "Cholesterol lowering and inhibition of sterol absorption by Lactobacillus reuteri NCIMB 30242: a randomized controlled trial." European journal of clinical nutrition 66.11 (2012): 1234-1241.
  • Konoshima, Takao, and Midori Takasaki. "Cancer-chemopreventive effects of natural sweeteners and related compounds." Pure and applied chemistry 74.7 (2002): 1309-1316.
  • Lionetti, E., et al. "Lactobacillus reuteri therapy to reduce side‐effects during anti‐Helicobacter pylori treatment in children: a randomized placebo controlled trial." Alimentary pharmacology & therapeutics 24.10 (2006): 1461-1468.
  • Shornikova, Aino-Vieno, et al. "Lactobacillus reuteri as a therapeutic agent in acute diarrhea in young children." Journal of pediatric gastroenterology and nutrition 24.4 (1997): 399-404.
  • Singh, Sunanda. "Antidiabetic, Antidyslipidymic and Antioxidative potential of methanolic root extract of Stevia rebaudiana (Bertoni) on Alloxan induced Diabetic Mice Sunanda Singh and Veena Garg Department of Bioscience and Biotechnology, Banasthali Vidyapeeth, Banasthali, Rajasthan, India." (2014). 
  • Tadhani, M. B., V. H. Patel, and Rema Subhash. "In vitro antioxidant activities of Stevia rebaudiana leaves and callus." Journal of Food Composition and Analysis 20.3 (2007): 323-329. 
  • Thompson, Matthew P., and Razelle Kurzrock. "Epstein-Barr virus and cancer." Clinical Cancer Research 10.3 (2004): 803-821.
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