Does Cooking Lower FODMAPs? Understanding Food Preparation on a Low-FODMAP Diet

October 11, 2025 •

4 min read

For up to 80% of people with Irritable Bowel Syndrome (IBS), a low-FODMAP diet can provide significant relief from digestive symptoms. A common question for those following this diet is, "Does cooking lower FODMAPs?" The answer is yes, specific cooking and processing techniques can help reduce FODMAP content in certain foods, offering more variety and flavor in your meals.

Quick Summary

Certain food preparation methods can reduce the FODMAP content in specific foods, making them more tolerable for individuals with sensitive digestive systems. These include boiling and draining water-soluble FODMAPs, using oil infusion for flavor, and leveraging fermentation processes to break down carbohydrates.

Key Points

Boiling Reduces FODMAPs: Water-soluble FODMAPs, such as fructans and GOS, can be significantly reduced by boiling food and discarding the water, particularly for legumes.
Oil Infusion is Safe: Since FODMAPs are not oil-soluble, you can safely infuse oil with the flavor of garlic and onion, provided you remove all solid pieces before adding other ingredients.
Fermentation Varies: Fermentation can lower FODMAPs in foods like sourdough bread and tempeh but can also alter or increase them in others. Use trusted resources like the Monash app.
Canned is Often Better: For legumes, the FODMAPs leach into the canning liquid over time. Draining and rinsing canned varieties can result in a lower FODMAP food than cooking them from scratch.
Firm Tofu is Low FODMAP: The pressing and straining process for firm and extra-firm tofu removes FODMAP-rich liquid, making it a safe choice for most on a low-FODMAP diet.

The Science Behind How Cooking Affects FODMAPs

Understanding the molecular properties of FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) is key to understanding how cooking can alter their levels. Some FODMAPs, such as fructans and galacto-oligosaccharides (GOS), are water-soluble. This means they dissolve in water during cooking. By discarding this liquid, you can effectively remove a significant amount of these FODMAPs.

In contrast, FODMAPs are not oil-soluble. This chemical property is the basis for a popular low-FODMAP cooking trick involving high-FODMAP aromatics like garlic and onion. Other techniques, like fermentation, rely on microorganisms that consume and break down FODMAPs, changing the food's composition. The effectiveness of any method depends on the specific food and the cooking conditions, highlighting why the Low-FODMAP Diet relies on tested serving sizes, often guided by resources like the Monash University FODMAP app.

Effective Cooking Techniques for Reducing FODMAPs

Boiling and Straining for Legumes and Vegetables

For certain water-soluble FODMAPs, boiling is a highly effective method. When high-FODMAP foods like dried lentils or kidney beans are boiled, the oligosaccharides (GOS) leach into the cooking water. Researchers believe that boiling and then straining the legumes can reduce the oligosaccharide content by a substantial amount. The key is to discard the water, as the FODMAPs are now in the liquid, not the food itself. Canned legumes are often lower in FODMAPs than freshly cooked ones for the same reason—the FODMAPs have leached into the canning brine over time, and the brine is discarded before consumption.

Fermentation for Breads and Soy Products

Fermentation uses bacteria and yeast to break down complex carbohydrates, including some FODMAPs. This is why traditional sourdough bread, which undergoes a long fermentation process, can have a significantly lower fructan content than regular bread. Similarly, the fermentation process used to create tempeh from soybeans reduces its GOS content, making it a low-FODMAP alternative to other soy products. However, fermentation does not always result in a lower FODMAP food, and in some cases, can even increase certain types. For example, some testing shows that sauerkraut can be higher in mannitol than raw cabbage. Always check the Monash app for tested serving sizes.

Oil Infusion for Flavor

Onion and garlic are staples in many cuisines but are high in fructans. Since FODMAPs are not oil-soluble, you can capture their flavor without the FODMAPs by using an oil infusion technique. To do this, you gently fry the chopped garlic or onion in oil for a few minutes. The flavor compounds infuse into the oil, but the fructans do not. It is crucial to remove all the solid pieces of garlic or onion from the oil before adding other ingredients, especially water-based ones, to prevent any fructans from leaching into your meal. Pre-made garlic-infused oil is also a safe, pantry-friendly option.

Pressing and Straining Tofu

Firm and extra-firm tofu are produced by pressing and straining the water from coagulated soy milk. This process also removes much of the water-soluble GOS content. As a result, firm and extra-firm tofu are considered low-FODMAP in typical serving sizes. In contrast, silken tofu is not pressed in the same way and retains its liquid, making it a high-FODMAP option.

Comparison of Cooking Methods and FODMAP Impact


Technique	How It Affects FODMAPs	Suitable Foods	Key Considerations
Boiling & Straining	Water-soluble FODMAPs (fructans, GOS) leach into the water, which is then discarded.	Legumes (lentils, kidney beans), some vegetables.	Ensure thorough draining and rinsing. Discard the cooking water completely.
Fermentation	Microorganisms consume FODMAPs over time, lowering their content.	Sourdough bread, tempeh, some dairy.	The outcome is food-specific; not all fermented foods are low-FODMAP.
Oil Infusion	Water-soluble FODMAPs do not dissolve in oil, allowing flavor extraction without FODMAPs.	Garlic, onion.	The solid pieces must be completely removed before other liquids are added.
Pressing & Straining	Removes FODMAP-rich liquid from the food.	Tofu.	Only applies to firm or extra-firm varieties; silken tofu is high FODMAP.
Canning	FODMAPs leach into the canning liquid over time.	Legumes (chickpeas, lentils).	Choose canned varieties, discard the brine, and rinse well.

Practical Tips for Your Low-FODMAP Kitchen

Prioritize Low-FODMAP Ingredients: The most reliable way to manage FODMAPs is to use naturally low-FODMAP ingredients. Cook with low-FODMAP vegetables like carrots, bell peppers, and spinach and choose tested grains like quinoa and rice.
Flavor with Safe Alternatives: Don't let go of flavor. Use a wide range of herbs and spices that are low-FODMAP, such as basil, thyme, cumin, and paprika. Ginger is also a great way to add warmth.
Be Mindful of Liquids: Always choose water-based liquids like broths without garlic or onion, or use homemade versions. In oil-based dishes, ensure all high-FODMAP solids are removed after infusing flavor.
Use Tested Servings: For foods where cooking affects FODMAPs, rely on the Monash University FODMAP app to guide your portion sizes. For instance, while canned lentils are low-FODMAP in a specific serving size, larger portions can still be high.
Reintroduce Carefully: The low-FODMAP diet is a process of elimination and reintroduction. Use the knowledge of how cooking reduces FODMAPs during the reintroduction phase to test your tolerance for foods you thought were off-limits.

Conclusion: Empowering Your Low-FODMAP Journey

Cooking is more than just combining ingredients; it's a tool for managing your nutrition, especially on a low-FODMAP diet. While high heat alone is not a magic bullet for eliminating FODMAPs, strategic use of techniques like boiling, fermentation, and oil infusion can make a significant difference. By understanding how water-soluble and non-water-soluble FODMAPs behave during cooking, you can confidently prepare flavorful, satisfying meals. This knowledge empowers you to expand your dietary variety, manage your symptoms, and take control of your digestive health with every meal you prepare.

Antonella Dewell RD, 5 Ways to Lower FODMAPs in Foods

Frequently Asked Questions

You can cook with onion and garlic by infusing their flavor into oil. Since fructans are water-soluble but not oil-soluble, they won't leach into the oil. Just be sure to remove all solid pieces of onion and garlic before adding any other ingredients.

Boiling can reduce the water-soluble FODMAP content of certain vegetables and legumes. The FODMAPs leach into the boiling water, which is then discarded. This method is particularly useful for reducing FODMAPs in foods like dried lentils and kidney beans.

Traditional sourdough bread is often low-FODMAP because the long fermentation process allows yeasts and bacteria to consume the fructans present in the grain. However, the FODMAP content can vary based on the fermentation time and specific culture, so it's best to consult the Monash app for tested products.

To reduce FODMAPs in legumes, use canned varieties and ensure you drain and thoroughly rinse them. Canned legumes are often lower in FODMAPs because the water-soluble oligosaccharides leach into the brine. Boiling dried legumes and discarding the cooking water is also effective.

Firm and extra-firm tofu are produced by pressing and straining the liquid, which removes much of the water-soluble GOS content. Silken tofu, which retains this liquid, therefore remains high in FODMAPs.

Yes, pickling can significantly lower the FODMAP content of certain vegetables, like onions and beetroot, due to the combination of fermentation and the acidic conditions of the brine. You should still check the Monash app for safe serving sizes.

While it is possible that very high temperatures might break down FODMAPs, the extent of this reaction varies unpredictably depending on the food and conditions. It is not considered a reliable method for reducing FODMAP content compared to techniques like boiling and draining.