How and why does diet/food ate affect the J pouch ?

I'm afraid that's the billion dollar question.  If we knew that we could treat or prevent inflammatory bowel conditions much better.  

The pouch just holds waste until it's full.  If you have inflammation of the pouch lining or gas etc then the pouch is going to feel fuller quicker with inflammation comes pain.

Sometimes the inflammation is a result of an immuno response, ie sometimes immune system treats a food as a threat and attacks it.  Actually a lot of conditions are thought to come from this sort of response from food.  M.E and fibromyalgia for example.  The curious question is how does the blood get to meet the blood to get a immuno response. The mechanism isn't fully understood but it's thought that bad diet or foods that disagree with an individual etc kill of the healthy bacteria in the gut, leading to an imbalance.  With the mucosal lining damaged food can slip from the bowel into the blood, the immune system then attacks the food infused gut lining causing more inflammation..  this is why steroids are used in severe cases, steroids basically switch off the immune system temporarily to allow the gut to heal and stop leading food.  Of course the underlying intolerance needs to be addressed too otherwise the issue will reoccur.

So the question is why the gut lining deteriorates in some people enough to allow food particles to leak. And what Can be done to prevent it.  Probiotics are thought to be part of the picture, but there's not an awful lot of research into that.  As with everything, genetics plays a part and there may be more than one cause of anything

I think most J-pouchers have no strong food-specific issues. I also think that most J-pouchers that do have food-specific issues would generally have them with or without the pouch. That being said, here are the paths I can think of:

Overdoing insoluble fiber can affect people with or without a J-pouch. Carbohydrates will tend to promote pouchitis in susceptible people. Some folks have real food sensitivities that aren't pouch-related, but are blamed on a J-pouch if they have a J-pouch. Some folks have random issues (e.g. adhesions) that get blamed on the last thing they ate before the trouble started. Some folks are prone to gassiness from particular foods and their J-pouch precludes normal farting for relief. Some have dysfunctional or badly constructed pouches that cause misery when anything passes through. Some have anal fissures or skin irritations that are exquisitely sensitive to stool thickness and (perhaps) acidity.

Thanks for both replies, theories  and opinions to my question.

I guess it's an impossible question to answer; there's so many possible causes and what sufferers believe may be the cause of their symptoms.

I just wondered whether underlying food intolerances was the cause.

My husband used to have to take the skin of apples etc.  Now, he doesn't because obstructions does not occur with the skins anymore. Though I worry. LOL