I have chronic constipation, do I need to fast for longer than 12 hours for the small intestinal bacterial overgrowth (SIBO) test?

No, but we do recommend following the restricted diet for 36 hours before the test.

This is because the slower gut transit time in some people with chronic constipation means food can 'sit' in your gut for longer than normal.

In practice, that means 2 days of the restricted diet instead of the usual 1 day.