Understanding Which FODMAP is Garlic and Onion

November 11, 2025 •

5 min read

According to Monash University, a leading authority on the low-FODMAP diet, both garlic and onion are high in a specific type of FODMAP known as fructans. This guide delves into why these alliums cause digestive distress for some and explores delicious, low-FODMAP alternatives that won't compromise on flavor.

Quick Summary

Garlic and onion contain fructans, a type of FODMAP that can trigger symptoms like bloating and gas in individuals with IBS. Since fructans are water-soluble but not oil-soluble, infused oils are a great way to add flavor. Safe alternatives include green parts of leeks and spring onions, chives, and asafoetida.

Key Points

Garlic and onion contain fructans: Both vegetables are high in fructans, a type of oligosaccharide that is poorly absorbed in the small intestine.
Fructans trigger IBS symptoms: The fermentation of fructans by gut bacteria produces gas, causing bloating, pain, and other digestive issues in sensitive individuals.
Fructans are water-soluble, not oil-soluble: This is the scientific basis for using garlic or onion-infused oils to add flavor without the FODMAPs.
Infused oils are low-FODMAP: Commercial or homemade garlic/onion infused oils are safe because the fructans do not leach into the oil, only the flavor.
Excellent alternatives exist: Green parts of leeks and spring onions, chives, asafoetida powder, and garlic scapes are great substitutes for flavor.
The diet isn't forever: The low-FODMAP diet has reintroduction phases to test personal tolerance levels and potentially bring back smaller amounts of certain foods.
Check for hidden FODMAPs: Be vigilant about checking food labels for added garlic, onion, and fructan-containing ingredients in processed foods.

The Fructan Factor: Why Garlic and Onion Cause Problems

For many, the first and most challenging change when adopting a low-FODMAP diet is removing garlic and onion. These ingredients are staples in countless recipes, forming the aromatic base for sauces, stews, and stir-fries across many cuisines. The issue lies with fructans, a subgroup of oligosaccharides (the 'O' in FODMAP) that are found in high concentrations in allium vegetables.

The Science Behind Fructan Intolerance

Unlike many other carbohydrates, fructans cannot be properly digested by the human small intestine because we lack the necessary enzymes. This means they travel intact to the large intestine, where they are rapidly fermented by gut bacteria. This fermentation process produces gas, which can lead to uncomfortable digestive symptoms such as bloating, cramping, and flatulence, especially in individuals with Irritable Bowel Syndrome (IBS). Furthermore, fructans are osmotically active, meaning they draw water into the bowel, which can contribute to diarrhea.

Water-Soluble vs. Oil-Soluble FODMAPs

Understanding the solubility of fructans is key to navigating low-FODMAP cooking. Fructans are water-soluble but not fat-soluble, a crucial piece of information that allows for flavor without the digestive side effects.

Water-Soluble: If you cook garlic or onion in a liquid, such as a soup or stock, the fructans will leach out into the broth. Simply removing the vegetable pieces afterward will not remove the FODMAPs, making the entire dish high in fructans.
Oil-Soluble: When you heat garlic or onion in oil, the flavorful compounds transfer to the oil, but the fructans do not. This makes garlic-infused and onion-infused oils a fantastic, low-FODMAP way to get that familiar taste. It is important to remove and discard all solid garlic and onion pieces before adding any other ingredients or water-based liquids.

Low-FODMAP Alternatives for Garlic and Onion

Thankfully, avoiding garlic and onion doesn't mean sacrificing flavor. There are several excellent substitutes and techniques to keep your meals delicious and gut-friendly.

Alternatives and Substitutions

Garlic and Onion-Infused Oils: As mentioned, this is a cornerstone of low-FODMAP cooking. You can purchase commercially certified oils or make your own by gently heating garlic or onion pieces in oil and then straining out the solids.
Asafoetida (Hing): This is a pungent Indian spice that imparts a distinct onion and garlic-like flavor to dishes when bloomed in hot oil. A small pinch is all you need, and it's a game-changer for many low-FODMAP cooks.
Green Parts of Alliums: The green, leafy parts of spring onions (scallions) and leeks contain very low levels of fructans and are safe to use in moderate amounts. The white bulb and greener parts closer to the bulb should be avoided during the elimination phase.
Chives: A relative of onions and garlic, chives have a mild oniony flavor and are low in FODMAPs. They are excellent as a garnish or added toward the end of cooking.
Pickled Onions and Garlic: Recent testing by Monash University found that pickling reduces the fructan content in onions and garlic, as the water-soluble FODMAPs leach into the brine. Ensure you drain the liquid completely before consuming.
Garlic Scapes: These are the green flower stalks of the garlic plant. They provide a milder garlic flavor and are low-FODMAP in specific serving sizes.

Comparison Table: Onion and Garlic Replacements


Alternative	Best For	Flavor Profile	Preparation Method	FODMAP Status	Note
Garlic/Onion Infused Oil	Sauteing, dressings, marinades	Rich, savory garlic/onion flavor	Heat solids in oil, strain, use oil only.	Low-FODMAP	Safe for most, DIY or certified commercial options.
Asafoetida (Hing)	Indian cuisine, curries, savory dishes	Pungent, garlicky, and onion-like when cooked.	Fry a small pinch in oil at start of cooking.	Low-FODMAP	Very potent; start with a tiny amount.
Green Parts of Spring Onions	Garnishes, salads, finishing dishes	Mild, fresh onion flavor	Chop and add raw or at end of cooking.	Low-FODMAP	Only the green tips are safe.
Chives	Eggs, potatoes, salads, garnishes	Subtle, delicate onion/garlic flavor	Finely mince and add to dishes.	Low-FODMAP	Can be added raw or at the end of cooking.
Leek Leaves (Green Parts)	Soups, stews, sautés	Mild onion flavor	Chop and sauté until soft; discards the white parts.	Low-FODMAP	Wash thoroughly and use only the dark green leaves.
Garlic Scapes/Shoots	Stir-fries, sauces, dips	Milder garlic flavor than raw cloves.	Chop and use fresh or cooked.	Low-FODMAP	Check serving sizes as higher amounts can contain fructans.

Cooking Strategies for the Low-FODMAP Diet

Successfully removing garlic and onion from your diet requires more than just knowing replacements; it's also about adjusting your cooking techniques. Focus on building flavor in new ways and being mindful of hidden sources of fructans.

Flavor-Building Tips

Herbs and Spices: Load up on other low-FODMAP herbs and spices like ginger, cumin, coriander, paprika, thyme, and rosemary. These can add depth and complexity to your dishes.
Citrus Zest: Add a bright, tangy element with lemon, lime, or orange zest, especially in marinades or vinaigrettes.
Umami-Rich Ingredients: Boost the savory taste, or umami, with ingredients like tomato paste, nutritional yeast, or soy sauce (check for added garlic/onion). Dried mushrooms are another excellent low-FODMAP source of umami.
Use FODMAP-Friendly Stocks: Be wary of conventional stock cubes and broths, which almost always contain onion and garlic. Use certified low-FODMAP stock powders or make your own homemade version.

Conclusion

For those with digestive sensitivities, the elimination of high-fructan foods like garlic and onion is a necessary step towards symptom relief. The good news is that a flavorful life is still possible with clever substitutions and techniques. By utilizing infused oils, asafoetida, and the green parts of spring onions and leeks, you can replicate the savory depth you're used to. Remember that the low-FODMAP diet is a process of identifying personal triggers, and many people can reintroduce small amounts of these foods over time. Working with a dietitian can provide personalized guidance to ensure a balanced and enjoyable diet in the long term.

Visit the Monash FODMAP website for comprehensive dietary information and certified products

How to Use This Information

Applying these principles to your daily cooking involves a bit of trial and error, but it's an achievable goal. Start by replacing garlic and onion in your favorite recipes with one or more of the alternatives listed above. Experiment with different combinations of herbs and spices to find new flavor profiles you enjoy. If using infused oils, ensure you are buying certified products or correctly making your own by discarding the solids to avoid any fructan transfer. By being intentional with your ingredient choices, you can effectively manage digestive symptoms while still creating delicious and satisfying meals.

Frequently Asked Questions

No, this method is not effective during the elimination phase of the low-FODMAP diet. Since fructans are water-soluble, they will leach out of the solids and into any liquid-based components of your meal. This means the dish will still contain high levels of FODMAPs, even if you discard the garlic or onion pieces.

Yes, properly prepared garlic-infused oil is low-FODMAP. The fructans in garlic are not oil-soluble, so the flavoring compounds transfer to the oil while the fructans remain in the garlic cloves. Always ensure you are using certified low-FODMAP oils or have completely strained out all solid pieces from your homemade version.

The green, leafy parts of spring onions (scallions) and leeks are low in fructans and are safe to consume in moderate amounts. The white bulbs of both are high in fructans and should be avoided during the elimination phase.

Asafoetida, also known as hing, is a resin from a plant that provides an onion and garlic-like flavor when cooked. It is a potent spice, so a small pinch is all that's needed. For best results, bloom it in hot oil at the start of cooking to mellow its strong, sulfurous scent.

Yes, pickled onions and garlic can be low-FODMAP in specific serving sizes, according to testing by Monash University. The pickling process reduces the fructan content as they leach into the surrounding liquid. Just make sure to drain the pickled items thoroughly before eating.

While some fermentation can reduce FODMAPs, the process in garlic and onions is specific. For example, pickling reduces fructans, but the FODMAP levels depend on the fermentation time and process. Generally, fermented garlic (black garlic) and typical lacto-fermented onions are still high in fructans. Always refer to certified sources like the Monash University app for specific serving sizes.

To add onion flavor to water-based dishes like soups or sauces, use a low-FODMAP certified stock or broth. Alternatively, you can use the green parts of leeks or spring onions, chives, or asafoetida powder. Avoid adding raw or sautéed onion to the liquid, as the fructans will infuse the entire dish.