FODMAPs: FOS, GOS & Mannitol

FODMAPs Beyond the Basics

In the FoodMarble app, you’ll notice we provide direct testing for Lactose, Fructose, Sorbitol, and Inulin. But these aren’t the only FODMAPs that can cause fermentation in your gut.

Other key FODMAPs include:

• FOS (Fructans)
• GOS (Galacto-oligosaccharides)
• Mannitol

In the food library, you can use filters to explore foods that contain these additional FODMAPs.

While we don’t currently offer testing packets for them, it’s still possible to explore your response by completing a custom challenge using foods that naturally contain these compounds. This can help uncover important insights into your unique digestive patterns.

Understanding FOS, GOS, and Mannitol

FOS (Fructans)

Found in foods like wheat, onions, garlic, and some fruits.

They are chains of fructose molecules:

• Short chains (2–9 units) → FOS
• Longer chains (10+ units) → Inulin

Humans lack the enzymes to digest fructans in the small intestine, so they travel to the large intestine where gut microbes ferment them.

Fermentation produces gases (like hydrogen) and short-chain fatty acids (SCFAs), which can trigger bloating, discomfort, and other symptoms in sensitive individuals.

GOS (Galacto-oligosaccharides)

Found in beans, lentils, and some grains.

GOS are another group of fermentable carbs that many people struggle to digest.

Common symptoms include gas, bloating, and digestive discomfort.

Mannitol

A sugar alcohol naturally present in some fruits and vegetables, and commonly added to sugar-free gum or “diet” products.

Poor absorption in the small intestine means it passes into the colon, where fermentation (and water retention) can trigger diarrhea, cramping, and bloating.

Why These FODMAPs Matter

Although you can’t directly test these FODMAPs with a packet, you can track your response to them. Because tolerance levels vary widely, knowing your personal threshold is more important than following a strict “avoid list.”

For example:

• You might tolerate a small amount of garlic (FOS) but struggle with larger amounts.
• You may find you can eat half a serving of beans (GOS) without symptoms, but a full serving causes bloating.
• You might react strongly to mannitol in sugar-free products but not to small amounts in vegetables.

Testing FOS, GOS, and Mannitol with Custom Challenges

To test your tolerance, you can run a custom challenge in the FoodMarble app using foods that naturally contain these FODMAPs.

This approach helps you:

• Confirm whether a specific FODMAP is triggering your symptoms
• Identify your personal threshold before symptoms begin
• Gain confidence in which foods you can safely enjoy, and in what amounts

Most people can tolerate some level of these FODMAPs, but finding your balance is key. We have a helpful guide on custom challenges with practical tips for testing each of these FODMAPs safely and effectively.

Updated on: 19/08/2025