A laboratory test called hydrogen breath testing is based on the fact that fermentation of malabsorbed carbohydrates results in bacterial production of excess hydrogen gas. The gas is absorbed into the bloodstream and excreted in the breath, where it can be measured.
To prepare for the test, you will be asked to fast for 12 hours before your appointment, and to refrain from smoking or brushing your teeth for two hours before the testing procedure begins. You should not have the test within two weeks of taking antibiotics.
Every laboratory has its own protocols for laboratory testing, but the following is a possible scenario. At the beginning of the test, your breath will be collected to establish a baseline. Then you will be given a solution of 25 grams of fructose dissolved in water. Your breath will be collected every 30 minutes over a three-hour period. The hydrogen in your breath will be measured. If there is a 20 parts per million difference between the baseline and any of the follow-up breath samples, your test is considered positive. Some labs test for methane gas in your breath as well.
Find out more about this book:IBS: Free at Last! Change Your Carbs, Change Your Life with the FODMAP Elimination Diet, 2nd Edition