What should I eat before my food intolerance test?

The Day Before Your Test

To prepare for your food intolerance test (also referred to as your Challenge), you'll need to complete a 12-hour fast before testing commences.

Before you begin your fast, eat a low FODMAP meal.

If possible, it's even better to follow a low FODMAP diet for the entire day before your test. This is particularly important if you think you have slow gastric transit, as it helps minimise fermentation from previous meals.

Your Last Meal Before Fasting

Your final meal before starting your 12-hour fast should be low FODMAP.

Suitable foods include:

• Potatoes
• White or basmati rice
• Rice noodles
• Meat, fish, or eggs
• A small handful of walnuts
• Cucumbers
• Carrots
• Zucchini (courgettes)

Choosing low FODMAP foods helps minimise the amount of fermentable food remaining in your digestive system, so your test measures your response only to the specific FODMAP being tested.

The Day of Your Test - Important Reminders

• Complete a minimum 12-hour fast before beginning your test.
• Do not eat anything before your Challenge other than the FODMAP substrate or test food you are testing.
• Brush your teeth before your test, but do not use mouthwash or chew gum. Mouthwash often contains alcohol, and many chewing gums contain sorbitol, both of which can affect your breath test readings.
• You may take small sips of still water before and during the test.

Updated on: 09/07/2026