Thanks for writing and I understand that you have some concerns about trying this new type of diet and specifically about Splenda and diary. Your questions are addressed in both the Fast Tract Digestion IBS and Heartburn books.
The Fast Tract Diet concept: The whole idea is that IBS, Heartburn and many other SIBO-related symptoms are driven by excess fermentation of undigested carbohydrates. Even though dairy products (except lactose free milk, etc.) all contain various amounts of lactose, some fermented dairy such as aged cheeses, and yogurt (go with the unsweetened) have much less lactose than milk for instance. These products are relatively low in overall fermentation potential and should not be a problem when consumed in limited quantities. Don’t overdo it however, since diary products also contain oligosaccharides which can cause symptoms in excess. You can also take a lactase supplement when consuming dairy.
As for Splenda, despite a solid safety record, some people do have concerns. Since it’s not a natural product, a bit of skepticism is healthy. As I discuss in my books, Splenda can easily be substituted for other sweeteners including stevia, dextrose (powdered glucose), erythritol (the one friendly sugar alcohol), or maltose (not for people with gluten sensitivity).