How does eating before a breath test throw it off. like if it's with glucose looking for gases. why would eating before test might make it positive?

Carbs in food: The hydrogen breath test provides information about the digestion of certain sugars (carbohydrates) and is performed to help diagnose lactose intolerance and bacterial overgrowth. If you eat before the test, the sugars in your food will interfere with the measurement of the amount of hydrogen produced by bacterial fermentation in your bowel and then eliminated by respiration through your lungs.