In initial animal studies, the research found that all of the artificial sweeteners caused increased blood sugar. Their theory was that the sweeteners change gut microbes — the bacteria in the stomach that, when balanced, help with proper digestion.

By transplanting microbes from artificial-sweetening using mice to germ-free mice, they were able to create glucose intolerance.

They went on to study a small group of people as well. The volunteers were healthy, and not consumers of artificial sweeteners. After consuming artificial sweeteners for 6 days at a regular dose, more than half developed impaired glucose tolerance — none had improved glucose tolerance.

The medical term for this is NAS-induced dysbiosis — meaning that non-caloric artificial sweeteners have caused an imbalance in the digestive and gut bacteria, that then increases glucose intolerance, and the risk of metabolic problems, including metabolic syndrome and pre-diabetes.

What happens when the sweeteners change your bacterial balance in the gut?

  • It interferes with your sense of fullness, and can cause you to eat more
  • It causes inflammation in the gut lining — which can lead to "leaky gut" syndrome
  • Leaky gut can allow bacteria to get into the bloodstream, increasing the risk of a number of diseases, including autoimmune disease

Another study looked at almost 400 nondiabetic patients, and found that long-term consumption of artificial sweeteners was associated with increased central obesity and glucose intolerance.

What About Stevia?

Stevia is a plant-based non-caloric sweetener that was not included in the study. There are some animal studies that have shown that stevia can be digested by gut bacteria, but there is no data regarding how this might affect metabolism.

Bottom Line?

If you are trying to lose weight, it's time to try eliminating all sugar substitutes, sugar, and frankly, all sugary foods and treats — as well as foods that quickly convert to sugar. For some people, simple carbohydrates like bread, pasta and cereal are metabolized so quickly into sugar in the body that there is very little difference between a bowl of cereal and a candy bar, as far as the metabolic impact.

Want to Learn More?

An interesting new book has just been published, The Swift Diet, by Kathie Madonna Swift RDN and Joe Hooper. This timely book looks at how to fix digestive problems and lose weight by changing the way you eat and altering your gut bacteria. The book discusses the impact of the bacteria, and how we can influence those bacteria, and ultimately, change them so that they resemble the bacteria that helps keep lean people lean, and healthy. A recommended read!

More information is available at the Swift Diet website.


Suez, J. et. al. "Artificial sweeteners induce glucose intolerance by altering the gut microbiota," Nature. Published online 17 September 2014 Abstract

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