Food can have an effect on the results of the H. pylori test, so you must fast in the morning to check for H. pylori. Generally, H. pylori testing is mainly performed through the carbon 13 or carbon 14 breath test. After drinking the isotope containing carbon 13 or carbon 14 markers during the test, H. pylori will produce a large amount of urease, which breaks down the urea into carbon dioxide and ammonia, and if the patient is not fasting, it will reduce the area of contact between the carbon 13 or carbon 14 markers containing carbon 13 or carbon 14 markers and H. pylori, resulting in low H. pylori test results. Moreover, a large amount of food eaten will also produce elevated carbon dioxide that is not caused by H. pylori, causing bias in H. pylori detection, therefore, it is generally recommended to check H. pylori on an empty stomach.