Do I need to fast for 14 hours before I take the small intestinal bacterial overgrowth (SIBO) test?

That's right: you need to fast for 14 hours before you take the test.

Start with a fasting breath sample before you drink the lactulose solution. By 'fasting' you must not eat for 8–12 hours before taking the test, but you can drink water.

Most people prefer to take the test first thing in the morning, as they would have naturally fasted overnight.

Then make another breath sample every 20 minutes after you've drunk the lactulose solution.

You also must avoid eating during the 3-hour test period.  

You also need to follow the test prep diet for a day beforehand, which you can find on the SIBO test kit instructions, along with everything else you need to know.