I have had mild IBSD for about 10 years. I saw a nutritionist last year who recommended taking a supplement of stomach acid on the basis that people lose stomach acid production after the age of 40, and that some individuals never produce enough acid. I'm a fit 63 year old male. I started taking pepsin and betaine (stomach enzyme and acid combination capsule). This seemed to really help.
A couple of months ago I listened to a podcast from The Glucose Goddess (on Diary of a CEO). One of her digestion "hacks" was to take a table spoonful of any vinegar, dissolved in water 10 minutes before the main meal. It doesn't have to be apple cider. I gave it a go and it seems to be working great. I wondered if anyone else had tried? I use this instead of the supplement at main meal time.
PS- If you decide to try it, make sure to suck through a straw as it could have an effect on tooth enamel.