Stevia rebaudiana is an herb native to Paraguay. The Guarani Indians of South America have been using stevia as a medicinal tea since the 16th century, and today the herb has fans across the globe. Stevia’s rise to fame has brought with it a cloud of conflicting “scientific” information and warnings making circles around the internet. Like the old game of Telephone, the more information gets passed around, the more the facts are exaggerated, conclusions are distorted, and mistruths are repeated until you don’t know what or whom to believe.
I’ve said for years that stevia is my go-to sweetener. Naturally, when I hear this could be affecting my ability to reproduce, I take such warnings very seriously!
In this article, we will take a look at the stevia controversy that has so many folks abuzz. I will present you with an evidence-based perspective on stevia, and then you can make up your own mind about whether or not to use it.
All Stevia Products Are Not Equal
Today’s commercial stevia products are very different from the stevia leaves used by the Guarani Indians. Whole leaf stevia is not approved by the FDA, even though some extracts of the plant are. Most commercially prepared stevia-based sweeteners contain isolates of the plant’s compounds (steviol glycosides) instead of the whole leaf—and therein lies some of the confusion. Some studies have looked at isolated compounds, and others the whole leaf.
Stevia leaf has two primary glycosides noted for their sweetness: stevioside and rebaudioside-A, or “reb-A” for short. Stevioside is reportedly 250 to 300 times as sweet as sucrose and reb-A is 350-450 times as sweet. Reb-A is the least bitter of the two and the one commercial products tend to favor.
Many stevia-based sweetener manufacturers are seducing consumers into believing their products are far more natural than they really are. This is concerning because stevia products are projected to account for 15 percent of the overall sweetener market by 2020, and consumers should know what they’re buying. (1)
The commercial process involves grinding up dried stevia leaves and using an elaborate extraction process to isolate the desired glycosides. The extract is so intensely sweet that it must be mixed with a bulking agent, such as cornstarch or other fillers, to make it usable. Common fillers include cane sugar, dextrose, sugar alcohols such as erythritol or xylitol, cellulose, or inulin. By the time it reaches you, the white powder in the little packet bears little resemblance to the original plant—in appearance or chemical profile.
Let’s take a look at some of the controversy; starting with the claim that stevia may have adverse effects on fertility.
Does Stevia Cause Infertility?
Some are warning consumers to avoid stevia because it may reduce fertility. The root of this is a 1968 paper claiming certain tribes in Paraguay (Matto Grosso Indians) used stevia tea as a contraceptive.
To investigate this claim, Professor Joseph Kruc of Purdue University performed a study using rats (1968). He fed the rats stevia (enormous quantities by human standards), and they produced fewer offspring than the control group. (2, 3, 4) However, the study has been described as having dubious scientific methodology, and multiple studies attempting to replicate its findings failed. Kruc later admitted that the rats’ lower fertility rates may have resulted from his “overdosing” them on the compound. (5)
Fast forward 20 years to Brazil, Professor Mauro Alvarez repeated the Kruc study and confirmed a contraceptive effect from stevia among female mice. However, his methodology was the subject of even more criticism. Many subsequent researchers were unable to find any fertility effects, so Alvarez eventually joined them in concluding that Stevia poses no threat to fertility. As for the Matto Grosso Indian tribes who supposedly used stevia for contraceptive purposes, at least one attempt by scientists to confirm the story reportedly failed.
There have been no human studies showing evidence of impaired fertility from stevia, yet the story continues to receive attention—even from the FDA, which continues to cite the above two studies as their main source of objection, in spite of all of the subsequent studies that refute stevia’s fertility effects. (6)
The bottom line is, there is no real evidence that stevia poses any reproductive risk, especially when used in normal human doses. As with anything, the rule is “all things in moderation.” If you have endocrine issues or are trying to get pregnant and the infinitesimal risk is going to keep you awake at night, simply avoid stevia. It’s not worth the stress—and stress IS a real health concern.
Does Stevia Cause Cancer?
Concerns have also been raised that stevia’s glycosides might cause genetic mutations and cancer. This stems from a 2008 review in which UCLA toxicologists found, in some test tube and animal studies, stevioside (but not rebaudioside-A) was linked with genetic mutations, chromosome damage and DNA breakage. (7) However, a different review refuted UCLA’s conclusions, finding a complete lack of evidence for genetic toxicity. They suggested that the first reviewers “appeared to be measuring processes other than direct DNA damage.” (8)
Artificial sweeteners were banned in Japan more than 40 years ago and since that time, the Japanese have been using stevia in abundance (the whole leaf variety) as well as doing an abundance of research. After more than 40,000 studies, they’re convinced stevia is safe. Some have even found that stevia may even exert anti-cancer effects. (9)
If there were anything about stevia products to warrant concern about cancer, it would be commercial concoctions such as Truvia, Pure Via and others, which are so highly processed that you really can’t even call them “stevia.” Truvia and the like undergo elaborate multistep processes involving multiple chemical agents, and if any traces of these agents are in the final products, then we obviously have a problem. This is why I recommend sticking to pure versions of the herb.
Does Stevia Spike Your Insulin?
There are valid concerns about the effect stevia has on insulin and blood sugar. We now know more about how artificial sweeteners affect the body. The Western diet is awash in unnaturally sweet foods and beverages, many of which are hundreds of times sweeter than natural sugars, and this wreaks havoc with the gut-brain signaling system.
Whenever you eat anything sweet, your body tends to react as though you’ve consumed sugar, regardless of the actual caloric load. When sweetness receptors on your tongue are triggered, your body prepares itself with a cascade of hormones and chemical messengers including insulin, leptin, ghrelin and others. Non-caloric artificial sweeteners fool the brain into thinking it’s getting glucose, bringing about kind of a “metabolic mayhem” that may result in even more weight gain and insulin resistance than sugar. (10)
But does stevia produce the same effects as artificial sweeteners? Interestingly, studies suggest it does not. Evidence is mounting that stevia can actually increase insulin sensitivity and improve glucose tolerance, even among diabetics. (11)
A 2010 study compared individuals consuming stevia with those consuming aspartame or sucrose. Those consuming stevia showed lower insulin levels after a meal, as well as more stable blood sugar and satiety levels. (12) Nevertheless, this should be evaluated on an individual basis. If you have diabetes, particularly if you’re taking insulin, it would be wise to monitor your blood sugar levels before and after stevia to make sure you don’t have a hypoglycemic response. Stevia can increase insulin sensitivity, which could conceivably cause a hypoglycemic reaction in those particularly susceptible.
Some have also expressed concern about stevia’s creating a glucose deficit in the body. I believe that if you have a diet rich in fresh vegetables, fruits and other whole foods, which are replete with natural sugars, you’re not going to be short on glucose or glycogen.
Stevia May Not Be as Gut-Friendly as We Thought
There is one recent study that is a bit concerning. In 2013, researchers found stevia may kill off beneficial gut bacteria, specifically Lactobacillus reuteri. The growth of Lactobacilli reuteri was inhibited by the presence of stevioside and reb-A, although the effect was only slight. (13) Lactobacilli are very important to your microbiome, from balancing lipids to conferring broad spectrum protection against pathogens. Prior stevia studies found no adverse effects on gut flora (14), but this seems like an important issue warranting further investigation, especially given the latest association between artificial sweeteners and unhealthy changes in gut flora that lead to obesity and chronic disease. (15)
Besides sweetening foods and beverages without torturing your pancreas, stevia has a number of other evidence-based health benefits, including the following:
- Increased HDL, reduced oxidized LDL, and reduced plaque volume (16)
- Significant blood pressure reduction, both systolic and diastolic (17)
- Anti-inflammatory and immunomodulating effects (18)
- Helps prevent diabetes-related kidney damage (19)
- Effective adjunct therapy against Borrelia burgdorferi (Lyme disease) (20)
Best Ways to Use Stevia
Stevia is an herb from the plant kingdom—so there are good, better and best ways to use it. Remember, there is a world of difference between real stevia and highly processed “stevia-based” sweeteners.
Plants’ health benefits come from a synergistic effect of all the compounds taken together, which often includes some type of “built-in” protection against potentially damaging effects. Once you extract a single molecule from a plant, such as reb-A, you are potentially bypassing the inherent safety mechanism typically found in whole-plant extracts. And then there is the issue of chemical processing and additives, which we’re already discussed.
The best way to use stevia is to do what the Guarani Indians have been doing for hundreds of years: brew the leaves as a tea. When you steep them, the sweetness is extracted, along with the natural phytonutrients. Many places now sell stevia plants, so try adding one to your herb garden! You can add stevia leaves to salads and other dishes, just as you would any other herb.
For practical purposes, the next best option is a high quality stevia product. They come in powders, tablets and liquids. Read labels carefully and choose the least adulterated version. Steer clear of additives such as corn oil, dextrose, erythritol, agave or other sugars. Inulin is okay as it’s a prebiotic fiber. Note that whole leaf powders will be green, not white.
All of that said, the best way to use stevia MAY be to not use it at all. Yes, you read that right. Let me explain…
Is it time to take a Sweet Retreat?
Stevia’s intense sweetness could be altering your food preferences. Westerners’ love of sweets is on an upward trajectory with no end in sight. Your body is exquisitely sensitive to sweet flavors, with receptors not only in your mouth but also in your intestine, liver, pancreas and brain. When people lay off the sweeteners, fruits begin tasting much sweeter and vegetables start popping with new flavors. Your body came equipped with taste buds for sour, salty, bitter and sweet—begin developing some of the others. If you sweeten foods habitually, even with stevia, it will be very difficult to overcome carb and sugar cravings.
Consider taking a break from sweet foods altogether—take a “sweet retreat,” to borrow a term from nutritionist Kathie Swift.
We don’t really know what the long-term effects of all these high-potency sweeteners will be decades down the road. We’re experimenting on ourselves, which as you know can end badly.
I think there is sufficient evidence to conclude that stevia’s health risks are minimal, as long as you stick to whole stevia leaves or whole leaf extract. If you need to follow a ketogenic diet or you’re doing intermittent fasting, stevia is a good option because it’s unlikely to throw off your blood sugar or cause an insulin spike. If you’re going to indulge your sweet tooth, it’s best to indulge in a way that’s minimally disruptive to your normal physiology, and stevia fits the bill.