Tom Yum Soup

A low FODMAP tom yum of shrimp, oyster mushrooms, lemongrass, galangal, kaffir lime leaves, bird's eye chilies, fish sauce, lime, and cherry tomatoes.

Prep 20 min

Cook 35 min

Serves 4

Gluten-freeDairy-free

Ingredients

• 6 cups (1.4 L) low-FODMAP chicken broth, or homemade shrimp stock from the reserved shells
• 1 lb (450 g) raw shrimp, peeled and deveined, shells reserved for stock
• 5 oz (150 g) oyster mushrooms, torn into bite-size strips (Monash rates oyster mushrooms low FODMAP at 1 cup / 75 g per serve)
• 2 stalks lemongrass, tough outer layer removed, bruised and cut into 2-inch lengths
• 1 thumb-size piece galangal (about 5 thin slices), or fresh ginger as a swap
• 5 to 6 kaffir lime leaves, lightly torn
• 2 to 3 fresh red bird's eye chilies, sliced (adjust to your heat; keep to about 28 g total)
• 2 tbsp garlic-infused olive oil
• 3 tbsp gluten-free fish sauce (fish, salt, and sugar only; no garlic or wheat)
• 3 to 4 tbsp fresh lime juice (about 2 limes)
• 1 tsp cane sugar or maple syrup
• 8 cherry tomatoes, halved (about 2 per bowl, within the low-FODMAP serve)
• Green tops of 2 scallions, thinly sliced
• 1/4 cup cilantro leaves, roughly torn
• Optional: up to 1/4 cup (60 ml) canned coconut milk for a creamy version (see Tips)

Instructions

Build the broth

1. If making shrimp stock, add the reserved shells to a pot with the 6 cups broth or water and simmer 10 minutes, then strain out the shells. Otherwise, start with the chicken broth.
2. Warm the garlic-infused oil in a large pot over medium heat. Add the lemongrass, galangal, kaffir lime leaves, and half the sliced chili. Stir for about 1 minute until fragrant.
3. Pour in the broth, bring to a gentle simmer, and cook uncovered for 12 to 15 minutes so the aromatics infuse.

Add the mushrooms and shrimp

1. Add the oyster mushrooms and cherry tomatoes and simmer 3 to 4 minutes until the mushrooms soften.
2. Add the shrimp and cook 2 to 3 minutes, just until they turn pink and opaque. Do not let the broth boil hard, which toughens them.

Season and finish

1. Take the pot off the heat. Stir in the fish sauce, lime juice, and sugar.
2. Taste and balance the broth: it should read salty, sour, and gently sweet with heat behind it. Add more lime juice or fish sauce a little at a time.
3. Ladle into bowls, leaving the lemongrass and galangal behind if you prefer not to fish them out later. Top with scallion greens, cilantro, and the remaining chili.

Tips & Substitutions

• Bruise the lemongrass, do not mince it. The stalks and galangal flavor the broth and are meant to be left in the bowl, not eaten, so bruising to release their oils is enough.
• Skip the jarred chili paste. Thai roasted chili paste (nam prik pao) usually lists onion, garlic, and shallot, so build the heat from fresh chili and the infused oil instead.
• Choose a clean fish sauce. Look for a brand listing just anchovy, salt, and sugar, and confirm it is gluten-free if that matters for you.
• Balance the seasoning off the heat. Lime juice stays brighter when added after cooking, and the hot-sour-salty ratio is personal, so taste before serving.
• For a creamy tom yum (nam khon), stir in up to 1/4 cup (60 ml) canned coconut milk at the end, keeping to that amount per Monash's low-FODMAP serve.
• Swap the protein for firm white fish, sliced chicken thigh, or firm tofu; adjust the simmer time until each is cooked through.

Why This Works

• Garlic-infused oil, not garlic cloves. Garlic's fructans are not oil-soluble, so the oil carries the flavor without the FODMAP load that garlic bulb would add.
• Oyster mushrooms in place of button mushrooms. Oyster mushrooms are low-FODMAP at 1 cup (75 g) per serve, while common white and button mushrooms carry mannitol.
• Homemade broth avoids hidden onion and garlic. Stock cubes and bottled broths usually list onion or garlic, so the linked broth or a quick shell-and-water stock keeps them out.
• Scallion greens for the onion note. The green tops are low-FODMAP where the white bulbs carry fructans, so they add that allium aroma without the white bulbs.

Storage

Store leftovers in the fridge for up to 3 days in an airtight container. The shrimp and mushrooms soften on reheating, so warm the soup gently over low heat rather than boiling it, and add a fresh squeeze of lime to wake it back up. Freezing is not ideal here because the shrimp and mushrooms turn rubbery, so it is better made fresh. If you plan to scale the recipe up, look up any ingredient in the FODMAP Foods app to see how its rating changes with portion size.