A recent scientific paper by Dr. Bernadene Magnuson and colleagues published in Nutrition Reviews discusses the metabolism of several low calories sweeteners and includes a section on the metabolism of stevia (steviol glycosides) as well. Here’s a Q&A with Dr. Magnuson on her paper, along with a link to the full publication.
1. What was the purpose of writing this review article?
There are many health professions recommending that people reduce their sugar consumption for various health reasons, but some are concerned about the safety of using low calorie sweeteners to help people lower sugar intake. This review article explains the research that shows all of the sweeteners are very efficiently metabolized and quickly excreted by the body. This helps to explain why stevia leaf extract (high purity steviol glycosides) is safe for everyone to use, including pregnant women and children.
Steviol glycosides are not absorbed intact but, once consumed, move into the large intestine where the colonic bacteria remove all the glucose units, leaving only the backbone, steviol. All of the different steviol glycosides are similarly metabolized to a common end product, steviol. In humans, steviol is absorbed into the body, quickly modified in the liver, and excreted in the urine as steviol glucuronide.
3. Is there evidence to show that the steviol glycosides or any metabolite gets stored in the human body from consuming stevia over time?
No, on the contrary, there is evidence that all metabolites are excreted so there is no storage.
4. Is natural-origin stevia (i.e., steviol glycosides) metabolized differently from the artificial sweeteners mentioned in your paper (aspartame, acesulfame potassium, saccharin, and sucralose)? Could you outline some of the key differences?
The different sweeteners are very different compounds, with different pathways of metabolism. Aspartame and steviol glycosides are both metabolized in the intestine and only their metabolites are absorbed into the body. For stevia, the steviol metabolites are excreted in the urine. For aspartame, the amino acid and methanol metabolites are used in the body, so there is no excretion. Both acesulfame K and saccharin are absorbed intact, and excreted in the urine. Sucralose is primarily not absorbed, and excreted in the feces.
5. Your paper mentions enzyme-treated/modified stevia. What is the difference between enzyme-modified steviol glycosides and natural-origin stevia leaf extract?
The enzyme-treated/modified steviol glycosides are steviol glycosides that have been extracted from the stevia plant but with the help of enzymes contain additional glucose or fructose units that have been added onto the naturally occurring steviol glycosides. This is done to improve the taste of the steviol glycosides. Whereas, natural-origin stevia leaf extract is extracted from the leaves of the stevia plant and purified, with no modifications to the naturally occurring steviol glycosides structures.
Studies have shown that the enzyme-treated/modified steviol glycosides are metabolized by the colonic bacteria to steviol, so the metabolism and final metabolites are the same as for naturally occurring steviol glycosides.
7. Based on research to date, does stevia (i.e. steviol glycosides) adversely affect a person’s gut microflora?
No. There are many dietary factors that affect a person’s gut microflora, but there is no evidence that the amount of steviol glycosides that people consume cause any adverse effects. There is also no evidence of any adverse effects on the gut microflora or gut function of animals fed very high amounts of steviol glycoside during safety testing.
8. According to your paper, how much stevia (i.e. steviol glycosides) does it take to replace the sweetness of about 5 teaspoons of sugar (25 g)? And, could you explain why there is this difference?
The sweetness of steviol glycosides varies somewhat depending the different steviol glycosides, but in general, about 1/200th to 1/300th of a teaspoon of steviol glycosides will provide the same sweetness as a teaspoon of sugar. In terms of grams, that is about 80 to 125 mg steviol glycoside to replace 25,000 mg (25 gm) of sugar. Or, about a teaspoon of Reb A, five grams, can replace about 1.5 kg of sugar.
The amount is pretty difficult for a consumer to measure out, so usually products designed to be used by the consumer, such as a tabletop sweetener, will be mixed with a carrier so it easier for the consumer to use. I think this is important to know, as people often worry that they are consuming a lot of a sweetener. But really only a very small amount, usually in mg quantity, is needed, due to the fact that the steviol glycosides are so much sweeter than sugar.
9. Why do some products sometimes combine stevia with another sweetener (caloric or low/non-caloric)? And is it safe to combine stevia with other caloric or low/non-caloric sweeteners?
People tend to want low calorie products to taste the same as those sweetened with sugar, and it is sometimes difficult to mimic that taste in every food product because of the differences in matrix and other food components. So for some products combining stevia with other low calorie sweeteners is one way to achieve a taste closer to a sugar-sweetened product but with lower sugar and calories and with lower impact on blood glucose.
And yes, eating different combinations of sweeteners is safe. To date, there is no scientific evidence to the contrary. We eat many different combinations of naturally occurring compounds in our diverse diets everyday, so eating combinations of safe ingredients is safe.
TO READ THE FULL ARTICLE
Publication Reference: Magnuson BA et al., 2016. Biological Fate of Low-calorie Sweeteners. Nutrition Reviews Vol 74(11):670-689.