Stevia, the maligned sweetener

Recognizing its harmful effects, more consumers are choosing products without added sugar. The result is a flourishing alternative sweetener market and confusion about which sugar substitutes are harmful or healthy. Stevia has been a leading natural sweetener until several well-meaning bloggers have maligned it as no better than synthetic sweeteners. So, what is the truth? Is stevia harmful or healthy?

What is stevia?

While the original sugar substitutes were synthetic chemicals (aspartame, sucralose, etc.), several natural options are now available (xylitol, monk fruit, erythritol, etc). One of those natural options is stevia, which is about 250 times sweeter than sugar (sucrose).

Stevia is a small perennial and subtropical herb native to South America. There are more than 150 species of stevia but the most prized variety is Stevia rebaudiana. Two sweet glycosides were isolated from its leaves by scientists in 1931— stevioside and rebaudioside. Both are sweet but stevioside leaves a stronger bitter aftertaste that some find disagreeable. Other naturally occurring glycosides are rebaudioside B and rebaudioside C.

Sweetness comparison (1)




(X sweeter than sugar)


(per tsp.)



Monk Fruit (Lo Han Guo)



Stevia (highly processed)



Stevia (Green leaf)









How stevia is processed

There are three main types of stevia: green leaf stevia, stevia extracts, and highly-processed stevia. Being aware of each type is important for choosing a stevia that is healthy rather than harmful.

  • Green leaf stevia — the type that has centuries of safe use behind it — is minimally processed. The leaves are dried and ground into a fine green powder. This type is approximately 30 to 40 times sweeter than sucrose and retains the health benefits of stevia.
  • Some stevia extracts further process the green powder with water and alcohol (minimally processed stevia extracts). The resulting extract is then subjected to an enzymatic process to reduce the bitter aftertaste. These are often liquid extracts and contain a variety of glycosides, not just one.
  • The worst extracts are highly processed — often undergoing dozens of steps — to create a processed stevia extract that resembles little of what it was in the leaf. These extracts are typically white powders or liquids and concentrated for the sweeter and less bitter part of the leaf (rebaudioside A). Chemical solvents are added to the rebaudioside after it is extracted from the leaf. Then the fillers and other ingredients are added to produce a very sweet and highly treated sweetener. In fact, one commercial stevia product (Truvia) admits on its website that it contains less than 1% stevia. (2) Interestingly, these are the extracts the FDA and other government regulatory agencies have approved for human consumption, but the whole leaf or crude stevia extracts are not.

Concerns over additives

Many bloggers point out that stevia often contains fillers and flavor enhancers like maltodextrin, sugar alcohols, dextrose, cellulose, and other natural flavors. This is true, especially among name-brand stevia products. However, the additive concern can be easily overcome by a savvy label reader. Some manufacturers also share their extraction method/process on their website.

The alleged harmful effects of stevia

Despite its centuries of safe use in Brazil, and Paraguay, and a long history of sage use in Japan several adverse effects have been attributed to stevia consumption. This list includes infertility, hormonal changes, low blood sugar, stressed adrenals, headaches, blood pressure dysregulation, dizziness, thyroid trouble, and even cancer. Let’s explore the evidence to support these allegations.

Infertility and hormonal changes may be a concern if large amounts are consumed. A 1999 study found that administering 6.7g/kg body weight of stevia extract produced functional changes to the male reproductive organs and resulted in lower testosterone levels in rats. (3A,3B) The problem with applying this study to humans is primarily the dose. In 2008, the Joint FAO/WHO Expert Committee on Food Additives established the safe daily intake of steviol glycosides as 4 mg/kg body weight. (3C) This dosage was reaffirmed in 2016. The dose of 6.7g/kg equates to about 469 grams daily in humans. To put this in perspective, you would have to consume over 117 teaspoons of stevia daily to equal this dose. This is an extreme dose that one would hardly be able to consume because of the overwhelming sweetness of stevia.

What about the effects of stevia on blood sugar? This has been tested in both animals and humans. Scientists administered stevia at a dose of 10mg/kg body weight for 28 days in diabetic rats. What the researchers found was that stevia exerted a beneficial effect that increased insulin secretion and reduced blood sugar levels. (4A) This effect appeared to be a result of stevia’s action on the pancreas cells that produce insulin (beta-cells).

Other scientists tested stevia in a food, rather than isolated, which more valid because stevia is typically not consumed alone. This research suggests that consumption of stevia cookies (as opposed to regular cookies) had no significant effect on blood glucose response two hours after consumption. (4B) This same study reported that the stevia cookies reduced hunger — certainly a positive finding for those trying to lose weight. A moringa cookie was also included in the study, which was able to reduce both hunger and blood glucose levels. Similarly, a test in healthy and obsess individuals who consumed tea and crackers with cream cheese sweetened with stevia determined that stevia significantly decreased glucose levels after a meal. (4C) Another clinical study found that stevia enhances glucose tolerance and reduces plasma glucose levels at a dose of 5g of leaf extract every six hours for three days. (4D) Lastly, a single dose of 1,000 mg of stevioside reduced glucose levels after a meal in diabetics. (4E) The current evidence suggests that stevia positively effects blood sugar regulation in healthy and diabetic individuals.

Some experts contend that stevia may stress the adrenal glands. The argument is that the sweet taste of stevia triggers the body to release insulin to shuttle glucose into cells. However, since no glucose exists in the bloodstream, adrenaline and cortisol are released to mobilize sugar stores (glycogen) from other sources (liver, muscles). This argument has some validity and this process might possibly occur. Anecdotal reports from individuals suggest a very small number of people may experience low blood sugar and weakened adrenals after ingesting stevia. But there is little evidence in the form of clinical studies to substantiate this.

The stevia causes cancer fears are a bit of a mystery. Laboratory research suggests that stevioside has an anti-cancer effect in breast, colon, and mouse skin cancer. (5A,5B,5C) Scientists concluded that stevia has no effect on pancreatic cancer development, growth, or death in a mouse model of pancreatic cancer. (5D) One study found that rebaudioside A did not damage DNA or cause genetic mutations in mice when administered at a dose of up to 2g/kg body weight. (5E) A more recent study concluded that stevia and its glycosides do not cause toxicity, cancer, DNA mutations, embryo or fetal harm, and have “therapeutic effects against several diseases such as cancer, diabetes mellitus, hypertension, inflammation, cystic fibrosis, obesity and tooth decay.” (5F) No research to support a carcinogenic effect could be identified. It appears that a connection between stevia and cancer is an exaggeration and not reality.

Current evidence suggests that stevia does influence blood pressure. A two-year, randomized, placebo-controlled study found that taking 500 mg of stevioside powder three times daily significantly reduced both systolic and diastolic blood pressure. (6) No significant incidence of adverse effects was noted between the stevia group and the placebo group. Although four people taking stevia reported gastrointestinal symptoms (abdominal fullness, nausea) and fatigue during the study. Until further clinical research is conducted, it may be prudent for people with low blood pressure to limit stevia.

Stevia doesn’t seem to have any effect on thyroid hormones. (7A,7B) This doesn’t mean that certain people don’t have a bad experience with stevia, some certainly do. Each of us is unique and the foods and supplements we consume will affect us differently. In addition, a small clinical study (16 participants) found that ingestion of 0.2g of stevia three times a day for one week modestly increased cortisol levels and affected the cortisol to cortisone levels in the morning. (7C) Elevated cortisol levels can disrupt thyroid hormone regulation, particularly in those with thyroid disorders. Again, caution should be exercised in people with thyroid disorders.

Steviol is the final product of metabolism and it essentially leaves the body without accumulating. (8) This suggests that stevia and its glycosides are readily metabolized and excreted by the body.

The bottom line

Reasonable use of stevia poses little risk of harmful effects in healthy individuals. People with adrenal fatigue, low blood pressure, low blood sugar, thyroid disorders, or cortisol imbalances may want to limit stevia, especially its long-term use. Your safest bet is to use reasonable amounts of a green leaf extract or minimally processed extracts. Highly processed stevia extracts that don’t contain fillers and additives have a long history of safe use as well but are less preferred. Chances are these are the ones in your favorite products and you have to decide if that product’s benefits outweigh the minimal risks.




Xylitol: Safe or harmful?

Xylitol is growing in popularity as a natural sugar substitute to sweeten various foods, gums, and oral care products. However, if you search the internet you find reports that xylitol is harmful and shouldn’t be consumed. So, what are the facts? Is xylitol a safe natural sweetener and sugar substitute with potential health benefits, or is it a toxic ingredient that should be avoided? Read on to discover the scientific facts of this often maligned sweetener.

What is xylitol?

This discussion needs to start with what xylitol is. Xylitol is a 5-carbon sugar alcohol (also called polyols) that has a crystalline, granular structure and sweetness comparable to sugar. Despite containing the name alcohol, xylitol contains no ethanol like alcoholic beverages. It is called a sugar alcohol like other sugar alcohols: sorbitol, mannitol, maltitol, isomalt, and lactitol  because its chemical structure places it in the alcohol family. It contains about 2.4 calories per gram (compared to 4 calories per gram for sugar). It is naturally found in some fruits and vegetables. Commercial xylitol is usually obtained from corn cobs or birch trees. Sugar alcohols are not processed the same as sugar absorbed and processed more slowly, which means that it provides fewer calories than the same amount of sugar and has less of an impact on blood sugar and insulin.

What is the problem or potential harm of xylitol and sugar alcohols?

Large amounts of sugar alcohols can cause gastrointestinal upset, such as gas, abdominal pain, and diarrhea.(1) However, the average person will not experience these effects unless they are consuming 50 grams or more per day. Indeed, research from the 1980s in the Soviet Union that administered 30 grams of xylitol per day observed that diarrhea and other side effects seldom occurred.(2) The same review of Soviet research concluded that xylitol is well-tolerated in children at doses of 20 to 35 grams daily for up to four weeks. People who are sensitive to sugar alcohols may experience GI symptoms — often severe — at much lower doses.

The most common report on blogs even among health professionals — is a concern about the toxicity of xylitol. This concern largely stems from animal research and appears to be misguided (more to come on this). It is important to remember that natural doesn’t always mean non-toxic. What determines toxicity is the dose of the substance (this principle is true of all substances regardless of whether it is natural or synthetic). A perfect example is water. Drinking too much water causes water intoxication (poisoning, seizures, and convulsions). Water is necessary to sustain life, but it can be toxic in excess. The same goes for many natural products, including xylitol.

What does research say?

Here is a brief summary of some of the research regarding toxicity in animals and humans.

  • Xylitol is extremely toxic to dogs (keep xylitol products away from man’s best friend) and can cause low blood sugar, seizures, liver failure, and death.(3)
  • Bladder tumors increased in mice when their diet consisted of 10% or 20% xylitol.(4) This is due to the conversion of a minor metabolite of xylitol called glycolic acid to oxalate. Increased oxalate in the urine predisposes mice to bladder stones, and in turn, bladder tumors. If humans consumed just 10% of their calories as xylitol, the average adult (based on a 2,000 calorie diet) would consume nearly 84 grams of xylitol daily. It would reach a whopping 167 grams if 20% of our calories came from xylitol.
  • At 20% of their diet, rats also experience an increased risk of tumor formation, but not at 10%.(4)
  • Humans do not readily convert glycolic acid to oxalate, and no increase in urinary oxalate levels has been observed even at doses of 1 g/kg body weight daily.(4) To put this in perspective, the average-sized person would need to consume 70 grams of xylitol daily to reach this level of consumption. Based on this no adverse effect, the study author concluded that humans exposed to normal levels of xylitol are at no risk of developing bladder tumors.

The current available research demonstrates that xylitol toxicity is species dependent, and not all animal studies can be directly correlated to humans. Current evidence in humans suggests it takes extreme amounts of xylitol to cause GI upset and potential harm.

Many products sweetened with xylitol (gum, breath mints, candy, protein powders) contain 1 gram or less of xylitol, meaning you would have to consume a significant amount of the products to even reach the safe level of 70 grams. Other products (jams/jellies — about 6 grams per tablespoon; baked goods) contain higher levels.

Benefits of xylitol

Research suggests that xylitol helps prevent tooth decay and cavities by preventing oral bacteria from sticking to teeth.(5) By preventing bacteria from sticking to teeth, xylitol reduces plaque formation. Remarkably, another review even found that xylitol can reverse the process of early cavities.(6) At least 5 grams of xylitol daily is necessary to produce a benefit to oral health, and some experts suggest 10 to 15 g in divided doses daily.(1) In addition, xylitol is a good choice for diabetics because it is low-glycemic and does not raise blood glucose or insulin levels like sugar.

Evidence-based conclusion

Based on the research and benefits of xylitol, it can be safely used in most adults at reasonable amounts (no more than 50 grams daily, but preferably less than 35 grams daily) and most children (less than 25 grams daily). Larger amounts may cause GI upset, while even small amounts may be problematic for sensitive individuals. Xylitol is beneficial for oral health, diabetics, and as a natural sugar substitute in reasonable doses, but should be avoided in excessive amounts.


(1) Makinen KK. Gastrointestinal disturbances associated with the consumption of sugar alcohols with special consideration of xylitol: Scientific review and instructions for dentists and other health-care professionals. Int J Dent. 2016;2016:5697907.

(2) Nesterin MF. Xylitol. Experimental and clinical investigations conducted in the USSR (review). Z Ernahrungswiss. 1980 Jun;19(2):88-94.

(3) Cortinovis C, Caloni F. Household food items toxic to dogs and cats. Front Vet Sci. 2016;3:26.

(4) Roe FJ. Perspectives in carbohydrate toxicology with special reference to carcinogenicity. Swed Dent J. 1984;8(3):99-111.

(5) Janakiram C, Deepan Kumar CV, Joseph J. Xylitol in preventing dental caries: A systematic review and meta-analyses. J Nat Sci Biol Med. 2017 Jan-Jun;8(1):16-21.

(6) Nayak PA, Nayak UA, Khandelwal V. The effect of xylitol on dental caries and oral flora. Clin Cosmet Investig Dent.  2014 Nov 10;6:89-94.