It’s hard to use GL to draw up an allowed foods list though. You’d need to qualify everything with portion sizes and foods that have to be eaten with it. There are additional factors, like cooking method and time, that would influence the end GL too, and with people suffering digestive issues you can’t really say what’s going to happen to the food. The majority of it could never end up in the bloodstream as glucose and just ferment in the bowels.
The GI is more straightforward when it comes to ruling out foods, although certainly you’ll want to consider the GL of your meals when you begin adding new foods in future. As far as GI is concerned, you might find this article about glycaemic profile interesting. None of these measurements are foolproof, so you’re generally better off looking at nutrition stats (grams of carbs and sugar per 100g in particular), and considering how you cook foods. Boiling and mashing vegetables will mean they’re digested much faster than a salad, for example.