Are Onions High FODMAP?
For most people following a low FODMAP diet, the short answer is yes, most onion bulbs are considered high FODMAP. The reason lies in their high concentration of fructans, a type of fermentable short-chain carbohydrate (oligosaccharide) that can be poorly absorbed in the small intestine. For individuals with a sensitive gut, these unabsorbed fructans draw extra water into the intestines and are rapidly fermented by gut bacteria, leading to uncomfortable symptoms like bloating, gas, and abdominal pain. This is why traditional yellow, white, and red onions, as well as shallots, are typically restricted during the elimination phase of the diet.
The Science Behind Water vs. Oil
A common cooking question is whether you can simply cook onions in a dish and remove the pieces before eating. This is a myth, particularly in water-based dishes like soups and stews. Fructans are water-soluble, meaning they will leach out of the onion pieces and infuse the entire liquid with FODMAPs. Conversely, fructans are not oil-soluble. This scientific fact is the basis for one of the most effective and widely used low FODMAP cooking hacks: creating onion-infused oil. By frying or sautéing onion pieces in oil and then removing them before adding other ingredients, you can capture the delicious onion flavor without the fructans.
Low FODMAP Onion Alternatives and Substitutes
Avoiding regular onions doesn't mean a life of bland meals. Several excellent substitutes and specific parts of the onion family are safe for the low FODMAP diet.
- Green Tops of Spring Onions (Scallions): The dark green, leafy parts of spring onions are a fantastic low FODMAP option. The fructans are concentrated in the white bulb, so simply use the green tops as a garnish or flavor base. This provides a mild, fresh onion taste.
- Chives: These delicate green herbs offer a gentle, onion-like flavor and are considered low FODMAP. They can be used fresh as a garnish or added to dishes during cooking.
- Green Tops of Leeks: Similar to spring onions, the dark green leaves of leeks are low in FODMAPs. They have a mild flavor and can be chopped and used in a variety of cooked dishes.
- Asafoetida (Hing): This Indian spice provides a pungent, garlicky, and onion-like flavor and is a lifesaver for many on the low FODMAP diet. A tiny pinch is all that's needed to add depth to your cooking. Some brands may contain wheat, so check for a gluten-free label if you have a gluten sensitivity.
- Pickled Onions: Monash University has tested pickled onions, noting that the fructans leach into the pickling liquid. Large pickled onions in vinegar have a low FODMAP serving size of 60g. It is recommended to eat the drained pickled onions.
- Vidalia Onions: Some specific types of onions have smaller low FODMAP serving sizes. Monash has tested Vidalia onions and found a 22g serving to be low FODMAP. However, it's crucial to stick to the recommended serving size to avoid symptoms.
Creating Your Own Onion-Infused Oil
Making your own infused oil is a simple and effective cooking strategy. Gently heat your preferred cooking oil, such as olive or canola, in a pan. Add large chunks of onion and sauté for several minutes to allow the flavor to infuse. Crucially, remove and discard all the solid onion pieces before adding other ingredients. Use the infused oil to sauté meats, vegetables, or as a flavorful base for sauces.
Comparison of Onion and Onion Alternatives on a Low FODMAP Diet
| Ingredient | FODMAP Status | Common Use | Flavor Profile |
|---|---|---|---|
| Yellow/White/Red Onion | High FODMAP (Fructans) | Base for most savory dishes | Strong, pungent, sweet when cooked |
| Green Scallion Tops | Low FODMAP (Safe serving) | Garnish, mild flavor addition | Mild, fresh, slightly peppery |
| Chives | Low FODMAP (Safe serving) | Garnish, flavor boost | Delicate, mild onion flavor |
| Green Leek Tops | Low FODMAP (Safe serving) | Cooked dishes, sautés | Mild, sweet, light onion flavor |
| Onion-Infused Oil | Low FODMAP (Safe for flavoring) | Sautéing, pan-frying | Oil takes on onion flavor |
| Asafoetida (Hing) | Low FODMAP (Small amounts) | Indian cuisine, seasoning | Pungent, garlicky, onion-like |
| Pickled Onions | Low FODMAP (60g serving) | Condiment, sandwich filling | Tangy, savory |
Conclusion: Finding the Right Balance
Successfully managing a low FODMAP diet and enjoying flavorful food is all about understanding which ingredients trigger your symptoms and finding delicious, safe alternatives. While most traditional onion bulbs are off-limits during the elimination phase due to their high fructan content, options like the green tops of scallions and leeks, chives, asafoetida, and onion-infused oil offer excellent ways to get that essential onion taste without the digestive distress. Remember that the low FODMAP diet is a temporary process of identifying your triggers, not a permanent eating plan. Many people find they can tolerate small amounts of some fructan-containing foods during the reintroduction phase.
To ensure you're following the diet safely and correctly, consult with a registered dietitian, particularly one who is trained in the low FODMAP approach. This will help you navigate the process effectively and build a diet plan that is both delicious and comfortable for your gut. For more detailed information on FODMAPs and food testing, the Monash University FODMAP blog is an excellent resource, confirming the safety of infused oils and other alternatives.
Frequently Asked Questions
Q: Can I cook with whole onions and just take them out before I eat? A: No, this is not a reliable strategy for water-based dishes like soups or stews. Since fructans are water-soluble, they will leach into the cooking liquid and infuse the entire dish with FODMAPs.
Q: Is onion powder low FODMAP? A: No, regular onion powder is concentrated onion and therefore high in fructans, making it high FODMAP. Some specialty stores offer low FODMAP onion replacement powders, but always check the ingredients.
Q: What about shallots? Are they low FODMAP? A: No, shallots contain high levels of fructans and are not suitable for the elimination phase of the low FODMAP diet.
Q: How can I safely get onion flavor into my food? A: The safest method is to use onion-infused oil. Fructans are not oil-soluble, so you can infuse oil with onion flavor by sautéing pieces and then removing them completely. The green parts of scallions and chives are also safe options.
Q: What is a safe serving size of green scallion tops? A: Monash University has determined that the green tops of scallions (spring onions) are low FODMAP in generous serving sizes, providing a safe and flavorful way to add an onion-like taste.
Q: Why do some people say they can tolerate small amounts of onion? A: The low FODMAP diet is temporary and personalized. During the reintroduction phase, some individuals discover they can tolerate small amounts of certain high FODMAP foods, including onions. This is specific to an individual's tolerance level.
Q: Are all pickled onions low FODMAP? A: Not all. Monash University testing showed large pickled onions in vinegar to have a low FODMAP serving size of 60g, likely because the fructans leach into the brine. Always check serving sizes and preparation methods, and ideally use a trusted app for guidance.
Q: What are fructans? A: Fructans are a type of fermentable oligosaccharide, a carbohydrate made of fructose units, that the human digestive system cannot break down. For sensitive individuals, they are poorly absorbed and fermented by gut bacteria, causing symptoms.
Q: What other seasonings can replace onion? A: Besides asafoetida, a variety of herbs and spices can add flavor, including fresh herbs like parsley, cilantro, and basil, or spices like cumin, paprika, and ginger, as long as they don't contain added onion or garlic.
Q: How does the reintroduction phase work with onions? A: After the elimination phase, you would test specific FODMAP groups to determine your individual triggers. This could involve challenging fructans by reintroducing onions or other fructan-containing foods in measured amounts under a dietitian's guidance.
Q: Can I grow my own low FODMAP scallions? A: Yes, you can re-grow scallion tops in water from the white bulbs. Simply place the bulbs with roots in a glass of water and change the water every few days to encourage new green growth.
Q: Is the low FODMAP diet a permanent solution? A: No, the diet is a short-term elimination and reintroduction process designed to identify specific food triggers. The ultimate goal is to return to a more varied and balanced diet by avoiding only the foods that cause you problems, or learning your tolerance level to them.
