Stevia, also known as "candyleaf", is a bush native to Central and South America. Extracts from the stevia plant are rapidly appearing in our food supply since the FDA recently recognized the "Generally Recognized as Safe" (GRAS) status of the extract, Reb A. This has raised the question of whether stevia products are allowed on the FODMAPS elimination diet.
Reb-A, the stevia derivative used in most products, is up to 300 times sweeter than sugar. It is used in very minute quantities, and has zero calories. With no sugars or fibers to be malabsorbed or fermented, it cannot be a FODMAP, therefore it is allowed on the FODMAPS elimination diet.
Be aware of what fillers are used in the stevia product, however. Many of the products are designed to be substituted for sugar on an equal volume basis. For example, you are supposed to be able to substitute 1 cup of stevia product for 1 cup of sugar. If less than one percent (1/300th) of the product is stevia, you have to ask yourself, "What is the other 99% of the white fluffy stuff in the measuring cup or packet"? Some of those fillers are definitely fermentable by gut bacteria, and shouldn't be consumed on the elimination phase of your FODMAPS elimination diet. Some manufacturers consider this a plus, and are market the stevia product as "pre-biotic", which translates to "food for gut bacteria". Although this may be fine for most people, in my opinion, IBS sufferers who are sensitive to FODMAPS could potentially experience symptoms when consuming these fillers in large quantities. I'd suggest waiting to try them during the fructans challenge phase of the diet.
If you can locate a stevia product with no fillers, such as a SweetLeaf SteviaClear, you can use it during the elimination phase. You may be able to locate stevia products that are filled with "allowed ingredients". For example, Truvía, manufactured by Cargill, can be used during the elimination phase, as it is filled with erythritol, which is not fermentable by gut bacteria.
Finally, don't forget that foods sweetened with good old-fashioned table sugar and maple syrup are allowed on the elimination phase of the FODMAPS diet. While it isn't necessary to use non-nutritive sweeteners such as stevia on the diet, it is nice to have options.
Update 9/23/09 Sun Crystals with Stevia is another product you can use during the elimination phase of the diet. It's ingredients are pure cane sugar and stevia.