We will begin by assuming you already have an IBS diagnosis, and the diet has been medically prescribed.
The #1 reason we see people not getting the results they want or expect is because they are not working with a FODMAP trained dietitian.
The diet was ALWAYS meant to be undertaken along with a FODMAP trained RD, but patients rarely get told this. They get an IBS diagnosis and sent out the door with a paper handout (maybe).
Please read this article: Have IBS? Top Reasons To Work with a Dietitian. You’ll see why it is imperative!