There is a sentence in Dr. Shen's paper that reads as follows.
Currently IPS is a diagnosis of exclusion based on the presence of symptoms of increased frequency of bowel movement with change in stool consistency, abdominal pain or cramping, and perianal or pelvic discomfort in the absence of endoscopic and histologic infammation. "Red-Flag" symptoms and sign such as nausea, vomiting, weight loss, fever, bloody bowel movement, and anemia are NOT consistent with IPS
Occasionally patients with celiac disease or proximal small bowel bacterial overgrowth may have similar presentations.....(as IPS)"
So there's the non answer to your question.
Before all of this it says that IPS pathology is multifactorial, patients using antidepressants or antianxiety agents would have a higher risk of having IPS, maybe having IBS before the surgeries is an indicator of having IPS after .... that Molecular mechanisms of IPS warrant exploration...... increased numbers of serotonin-expressing cells in the pouch mucosa has been demonstrated in patients with IPS, indicating a possible role of overactivation of the neuroenteric system.
It looks subjective to a point but there are tests to rule out celiacs and sibo.
There are so few of us with j-pouches there are not enough of us to test in order to have proper control groups in my opinion.
BTW in the summary it says: "Patients with inflammatory and noninflammatory diseases after IPAA often present with nonspecific symptoms that compromise their quality of life."
No kidding