Stevia is an herbaceous family of plants, 240 species strong, that grows in sub-tropical and tropical America (mostly South and Central, but some North). Stevia the sweetener refers to stevia rebaudiana, the plant and its leaves, which you can grow and use as or with tea (it was traditionally paired with yerba mate in South America) or, dried and powdered, as a sugar substitute that you sprinkle on. It's apparently quite easy to grow (according to the stevia seller who tries to get me to buy a plant or two whenever I'm at the Santa Monica farmers' market), and the raw leaf is very sweet.
Most stevia you'll come across isn't in its raw, unprocessed form, but in powdered or liquid extract form. The "sweet" lies in the steviol glycosides - stevioside and rebaudioside - which are isolated in these extracts. Some products use just one, while others use both stevioside and rebaudioside. Stevioside is the most prevalent glycoside in stevia, and some say it provides the bitter aftertaste that people sometimes complain about; rebaudioside is said to be the better tasting steviol glycoside, with far less bitterness. Most of the "raw or natural" stevia products use the full range of glycosides, but the more processed brands will most likely isolate one or more of the steviol glycosides. The popular Truvia brand of stevia products uses only rebaudioside, as do both PureVia and Enliten. Different brands provide different conversion rates, but compared to sucrose, stevioside is generally about 250-300 times as sweet and rebaudioside is about 350-450 times as sweet.
Does Stevia Affect Insulin?
There is one in vitro study that showed stevioside acts directly on pancreatic beta cells to stimulate insulin secretion and another which shows similarly insulinotropic effects of rebaudioside, which may give you pause. Insulin secretion sounds like an insulin spike, no? And since we tend to be wary of unneeded insulin spikes, maybe we should avoid stevia. It's not so simple, of course. For one, this was an in vitro study, performed in a super-controlled laboratory petri dish type setting; this was not an in vivo study of animals or people eating stevia in a natural, organic way. The results of in vitro studies are notorious for not panning out when you try to replicate them in vivo. Secondly, insulin secretion isn't necessarily a bad thing. I mean, we need it to shuttle nutrients into cells, and we'd die without it. As I mentioned in the dairy post a few weeks back, insulin is millions upon millions of years old. It's been preserved throughout history because it's an essential hormone. It's not always the bad guy, especially if you're insulin sensitive.
In fact, the evidence is mounting that stevia actually is an insulin sensitizer that can aid in glucose tolerance and clearance after a meal. The Japanese have been using stevia for decades in the treatment of type 2 diabetics. Let's look at a few recent studies. In fructose-fed rats, a single instance of oral stevioside increased insulin sensitivity and reduced postprandial blood glucose in a dose-dependent manner. The same study also found that diabetic rats given stevioside required less exogenous insulin for the same effect. Taken together, these results suggest that stevia may not just be a good sugar substitute for diabetics, but an effective supplement for treatment of their insulin resistance.
Another study looked at the postprandial effects of stevia, sucrose, and aspartame in human subjects. Compared to sucrose eaters, stevia eaters showed lower postprandial blood sugar levels. Compared to both sucrose and aspartame eaters, stevia eaters had far lower postprandial insulin levels. Furthermore, eating stevia did not induce increased appetite throughout the day, indicating stable blood sugar and satiety levels. Another strike in stevia's favor.
Any Other Effects?
There are other potential benefits to using stevia unrelated to its apparent benefits on glycemic control. Here are a few studies I was able to dig up:
-When combined with inulin, a soluble prebiotic fiber, low-dose stevia increased HDL while lowering overall lipids in male rats. Alone, low-dose stevia lowered cholesterol without the potentially beneficial effect on HDL. It's also useful to note that high-dose stevia negatively affected some toxic parameters - so don't eat spoonfuls of stevia (not that you would) - but long term low-dose stevia was deemed safe.
-Lipid numbers are fun and all, but we're really interested in avoiding atherosclerotic plaque buildup. In mice treated with stevioside, oxidized LDL was reduced, overall plaque volume was reduced, and insulin sensitivity increased. Overall, atherosclerosis was reduced in the stevioside-treated mice. I couldn't dig up exactly how they were "treated," however, but they were given doses of 10 mg/kg.
-In another study, mice memory was impaired by administration of scopolamine, an anticholigernic found in the intensely hallucinogenic jimson weed (or devil's weed) and datura. Impaired mice were given oral stevioside (250 mg/kg) and tested for memory retention. Memory deficit was largely reversed with administration of stevioside, which also reduced the brain oxidative damage caused by scopolamine. Clinically relevant? Perhaps not, but it's interesting.
-A two-year randomized, placebo-controlled study of Chinese patients with mild hypertension (which a rather large swath of society probably suffers from) found that oral stevioside intake significantly reduced systolic and diastolic blood pressure. Patients either took a 500 mg capsule of stevioside or a placebo three times a day for two years. The hypertension situation improved across the board and no downsides were reported or detected. Also of note is the fact that slightly more patients in the placebo group developed left ventricular hypertrophy, a pathological thickening of the heart muscle. Of course, another study using far lower doses (up to 15 mg/kg/day) found no anti-hypertensive effects, so it appears that the dose is key. Maybe somewhere in the middle works well, as one study in hypertensive dogs showed: they used 200 mg/kg to normalize blood pressure in the canine subjects.
We can think about stevia as a Primal sugar alternative with some potentially therapeutic effects. Kind of like cinnamon or turmeric, we don't consume it for the calories or as literal fuel for our bodies, but for flavor, variety, and, possibly, the health benefits. It may induce insulin secretion, but it increases insulin sensitivity, reduces blood glucose (i.e., the insulin is doing its job), and does not increase appetite. It's been used by humans for hundreds of years and by diabetic patients in Asia for decades. The goofy health food store dude who claims aspartame was created by Donald Rumsfeld to give us cancer may be a vociferous supporter of it, but don't hold that against stevia. I'm a fan of the stuff and recommend it as a Primal way to satisfy a sweet tooth.
I've been into stevia for about 10 years now and it has been a very good thing for me. I think it tastes better than sugar. A friend was diagnosed with type 2 diabetes so I gave him some stevia to try. No more high blood sugar for him now. Ran out of my whole leaf stevia so I thought I would try Truvia. It tasted terrible and made me feel sick! I was browsing the stevia at my local health food store and was angry to find that one product had grapefruit seed extract in it. (Grapefruit seed extract = headache) I don't like it one bit that these companies are taking a perfectly good and healthy herb like stevia, refining, "standardizing" and adding unnessiary ingredients that are known to be harmful. This whole anti-stevia sentiment is coming from the sugar cane empire and always has.