My son has been diagnosed with an ileus(no surgery). how can i find out cause and ways to prevent. he was told by his gastro to eat more fiber...

Multiple causes: Your son has a ileus. He has most likely had a recent illness. He may have a respiratory virus etc. This can cause ileus. Electrolytes like potassium being abnormal can also cause ileus. It does not mean blockage. Time and support usually work. Narcotic medication can also cause ileus. A diet high in fiber may help minimize ileus but treating underlying cause is still important.