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 — and symptoms can sometimes be linked to others too.

Other key FODMAPs include:

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

👉 You can use the filters in our food library to explore which foods 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.

Many people struggle to digest GOS. Common symptoms include gas, bloating, and digestive discomfort.

💡 If you’ve ever felt gassy after beans or lentils, GOS might be the reason.

Mannitol

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

Because it’s poorly absorbed in the small intestine, it passes into the colon, where fermentation and water retention can cause diarrhea, cramping, and bloating.

Why These FODMAPs Matter

Although you can’t directly test these FODMAPs with a packet currently, you can track your response to them. And because tolerance varies widely, your personal threshold matters far more than 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.

✅ This is why testing yourself, not just following lists, helps you feel more confident and less restricted.

Testing FOS, GOS, and Mannitol with Custom Challenges

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 at least some level of these FODMAPs. Finding your balance is key — and it’s what will allow you to keep variety in your diet without unnecessary worry.

We have a helpful guide on custom challenges with practical tips for testing each of these FODMAPs safely and effectively.

Updated on: 01/09/2025