replacing them with white versions at least sometimes. This is recommended until 5yo in the UK.
A tip if you like to eat brown pasta, you can cook a small portion of white pasta in with your own brown pasta which greatly reduces the number of pots on the stove and amount of extra work involved to provide LO with a slightly different meal. We eat white pasta but my DS was highly frustrated by spaghetti even though he had happily eaten it a couple of times, basically he couldn't get the food in his mouth fast enough and found it an ordeal to eat. For a while I dropped a handful of pasta twists into the pot with our spag and then just fished them out when I drained. Worked a treat. I know some pastas have a slightly different cooking time but it always worked out fine for DS. I did this until the day he got upset that he wasn't served exactly the same as mummy and daddy. Kids eh?
With bread, crumpets, pita breads, chapati etc you could perhaps by a white version and freeze it so that you can lift out one portion for LO and the main meal is the same but LO gets the white version until older.
WRT constipation. I found I could naturally control my DS's poo with prunes and carrots. If he was a bit too firm I gave him a ready to eat, pitted, prune or two as part of his meal (he loved them and would just eat them straight like that) and in addition I avoided serving carrots for a day or two. If he was a little too loose I served carrots (and no prunes) which firmed things up. I am sure other people use other foods in a similar way, it's great if you can discover a couple of foods like this which you LO likes.