Is Stevia Safe?

steviaWell we’ve hit the major artificial sweeteners in previous posts in this series. Today we look at a natural sweetener, stevia.

Stevia (stevia rebaudiana) is a sweetener that many people have been using for hundreds of years. It is native to Central America and South America. The leaves are around 40 times sweeter than sugar and the extract is about 300 times sweeter. It dissolves very quickly in and can have somewhat of a bitter aftertaste.

So we can’t call stevia an artificially sweet seduction since it is natural. But is it another sweet seduction or is it a winner to make things oh so wonderfully sweet?

Study Time!

In a study of rats, 0.5mg/kg of stevia lowered blood glucose levels in diabetic rats and glucose tolerance testing in normal rats. It also reduced insulin sensitivity in the diabetic rats and enhanced insulin secretion and insulin utilization.1

So even though insulin increased, sensitivity and utilization of the insulin was better. That is important to remember. If insulin merely goes up and isn’t used because of sensitivity, that is bad. If insulin goes up and is used, like in healthy individuals that’s ok. That’s the way it’s supposed to be.

In another study of diabetic induced rats, stevia was used to compare blood glucose levels with normal and diabetic controls. Subjects were fed 150mg/kg, 200mg/kg and 250mg/kg of stevia per day. Significant decreases in blood glucose were measured as well as non-significant decreases in body weight. Glimepiride (a diabetic drug which increases insulin secretion) was also used as a comparator. Glimepiride lowered blood glucose significantly more than stevia at all doses.2

In yet another rat trial, rats were made diabetic and given stevia, methi seeds, stevia with methi seeds, or glimepiride. They were followed for 60 days. Blood glucose decreased the greatest with glimepiride, next with methi and stevia combo, then methi alone, then with stevia alone. Stevia did create a significant effect on blood glucose by itself. 3

Another study shows that rats fed lots of fructose were able to decrease insulin resistance with a good ol dose of … guessed it, stevia.4

In an actual human study, subjects were given preloads of stevia, aspartame or sucrose before being fed a meal. 20 min after the meal blood was drawn and glucose and insulin measured. Compared to sucrose, aspartame and stevia produced less postprandial glucose levels. Stevia produced significantly lower insulin levels compared to aspartame and sucrose.

In another human study in subjects undergoing glucose tolerance tests, 5 grams of steavia leaves were given at 6 hour intervals for 3 days. The groups were separated into stevia and an aqueous arabinose solution. Stevia increased glucose tolerance and decreased glucose levels during the study.6

Other effects

Stevia appears to have some fertility effects, at least in rats. In one study a water decoction (a way of extraction by boiling chemicals from herbs or plants) was given to rats that were fertile. The infertility continued for 50-60 days after intake stopped. To the researchers no other effects were noticed. This was in females.7

In male rats in chronic (60 days according to the paper) administration produced,

“produced a decrease in final weight of testis, seminal vesicle and cauda epididymidis. In addition, the fructose content of the accessory sex glands and the epididymal sperm concentration are decreased. Stevia treatment tended to decrease the plasma testosterone level” 8

So these poor buggers not only had smaller testes but also less sperm and decreased testosterone. Not exactly a thrilling side effect.

Gut Flora

Stevia doesn’t appear to alter gut flora which is a good thing. The bacteria are able to alter it to steviol however that was the end of it. The tests were done with samples from human donors in vitro.9, 10  How’s about that for donating to science!? We can suppose that this would translate over to a real life human intestine but you never know in these types of studies. This information is promising though.

Blood Pressure

In a study in China, participants were given 500mg of stevia 3 times per day for two years vs placebo and blood pressure was measured. A significant decrease was noted after 1 week. The change was from 150 [7.3] to 140 [6.8] mm Hg; DBP, from 95 [4.2] to 89 [3.2] mm Hg. That’s not too bad. A side note from this study is that more people on placebo had a thickening of the left ventricle than people on stevia (34% vs 11.5% respectively) Quality of life scores were better with stevia. There was no difference in adverse effects between groups.11

Another study found no difference in blood pressure using 3 different doses of stevia, up to 15mg/kg/day.12 This for me would be the 500mg three times daily. The difference in this study is that it was dosed twice daily rather than three times daily. Is this enough to make a difference? I don’t know. I could develop all kinds of protocols for a study to look at these questions but the real question is does this harm you? In both of these studies no adverse effects were seen compared to placebo.

Some have claimed that stevia will raise epinephrine and cortisol. I can’t find any evidence to support this. If anyone has anything I’d love to see it. If that is true it would be a big ding against stevia but again I can’t find evidence to support it.

Stevia may also have oxalates in them which can be problematic for people with kidney stones made from the same substance. I can totally buy that the leaves have them, but I haven’t been able to confirm the extract.

Final thoughts….for now

It looks as though stevia is probably OK for use. If a person is having problems with infertility it may be best avoided. Some forms are sold with other fillers like maltodextrin so they may not truly be zero calories, although if you’re using 1 packet of the stuff it will be less than 4 calories. But if you’re using bulk you’ll have to take care like you would with sucralose, which you’ll never find in my house. Nasty stuff that is!

If you’re diabetic or worried about blood sugar then it appears stevia is beneficial, at least to some degree. Like I always say, try it out and see what happens to you because you and I are not the same people, and neither of us are rats.

You probably won’t find me using 500mg caps of stevia for blood pressure reduction either since I feel that a good diet and some movement will likely take care of that, but it won’t raise it either (unless you’re eating it with junk). From time to time you might see me sweeten something with it, but not regularly and certainly not in bulk. I like my testes the way they are thanks.


1.Chen, Tso-Hsiao, et al. “Mechanism of the hypoglycemic effect of stevioside, a glycoside of Stevia rebaudiana.” Planta medica 71.02 (2005): 108-113.

2.Sumon, M. H., et al. “Comparative efficacy of powdered form of stevia (Stevia rebaudiana Bertoni) leaves and glimepiride in induced diabetic rats.” Bangladesh Journal of Veterinary Medicine 6.2 (2008): 211-215

3.Rafiq, Kazi, et al. “Comparative efficacy of stevia leaf (stevia rebaudiana bertoni), methi seeds (trigonella foenum-graecum) and glimepiride in streptozotocin induced rats.” International Journal 2229 (2011): 7472.

4.Chang, J-C., et al. “Increase of insulin sensitivity by stevioside in fructose-rich chow-fed rats.” Hormone and metabolic research 37.10 (2005): 610-616.

5.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.

6.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…[et al.] 19.6 (1986): 771.

7.Planas, G. M., and J. Kucacute. “Contraceptive Properties of Stevia rebaudiana.” Science (New York, NY) 162.3857 (1968): 1007.

8.Melis, M. S. “Effects of chronic administration of< i> Stevia rebaudiana</i> on fertility in rats.” Journal of ethnopharmacology 67.2 (1999): 157-161.

9.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.

10.Koyama, E., et al. “In vitro metabolism of the glycosidic sweeteners, stevia mixture and enzymatically modified stevia in human intestinal microflora.” Food and Chemical Toxicology 41.3 (2003): 359-374.

11.Hsieh, Ming-Hsiung, et al. “Efficacy and tolerability of oral stevioside in patients with mild essential hypertension: a two-year, randomized, placebo-controlled study.” Clinical therapeutics 25.11 (2003): 2797-2808

12.Ferri, Letícia AF, et al. “Investigation of the antihypertensive effect of oral crude stevioside in patients with mild essential hypertension.” Phytotherapy Research 20.9 (2006): 732-736.