Hidden garlic and onion: foods that contain them and how to spot them

Garlic and onion most often hide in stocks and broths, bouillon cubes, pasta and tomato sauces, curry pastes, salad dressings, marinades, seasoning blends, soups, dips and restaurant base sauces. They are rarely the star of a dish, so they are easy to miss. If garlic and onion are among your triggers, these are the places to check first.

Monash University, the team that developed the low-FODMAP approach, notes that both onion and garlic are high in fructans, one of the FODMAP groups. Because they are used as a flavor base in so many cuisines, they turn up in foods you might not think of as "oniony" at all.

This guide covers where they hide, how US food labels name them, what to ask when eating out, and how to keep plenty of flavor in your cooking. If you are new to FODMAPs, start with our low-FODMAP guide for IBS.

Fructans are carbohydrates that the small intestine doesn’t fully digest. According to the NIDDK, bacteria in the large intestine break down carbohydrates that weren’t digested higher up, and this produces gas. For people with a sensitive gut, that can mean bloating, pain or changes in bowel habit.

Not everyone reacts to fructans, and people who do react may tolerate different amounts. That is why Monash describes the low-FODMAP approach in three steps: a short elimination phase, a challenge phase where FODMAP groups are tested one at a time, and a personalized long-term phase that relaxes restrictions as much as possible. Monash recommends doing this with a dietitian who has specialty skills in IBS.

US food labeling rules help here, but they also leave some gaps. Under the FDA regulation on flavor labeling, 21 CFR 101.22:

• "Spice" excludes garlic and onion. The definition of spice leaves out substances traditionally regarded as foods, and names onions, garlic and celery as examples.
• Garlic powder and onion powder must be named. Powdered or granulated onion and garlic are treated as food rather than flavor, and must be declared by their common names.
• "Natural flavor" is broad. It can cover essential oils, essences or extractives from vegetables and other plant sources. The label doesn’t have to say which plant they come from.

In practice, that means "garlic powder", "onion powder", "dehydrated onion" or "garlic" should appear by name on FDA-regulated packaged foods. The harder cases are vague terms like natural flavor, flavoring and seasoning, which can’t tell you whether a garlic or onion extract is present. Meat and poultry products are regulated by the USDA rather than the FDA, so their labels can look a little different.

These are the aisles where garlic and onion most often turn up. It isn’t a list of foods to avoid, just the labels worth a second look:

• Stocks, broths and bouillon. Monash lists stock as a low-FODMAP option only when it is made without onions or garlic.
• Soups and ready meals, which usually start with a stock or an onion base.
• Pasta sauces, salsas and tomato-based sauces.
• Salad dressings and marinades. Registered dietitian Kate Scarlata notes that commercial salad dressings and marinades often contain garlic and onion.
• Seasoning mixes and rubs. Monash suggests steering clear of seasoning mixes and blends during elimination unless you can check every ingredient.
• Curry pastes, stir-fry sauces and gravy mixes.
• Dips and spreads, such as hummus, tzatziki and flavored cream cheese.
• Flavored crackers, chips and snacks, especially "sour cream and onion" or "garlic" varieties.
• Processed meats, such as sausages, burgers and deli meats.

Menus rarely list every ingredient, so restaurant food is where hidden garlic and onion catch people out most. Monash’s eating-out tips point to sauces, dips and dressings, rich dishes like curries, and stock-based dishes such as soups and risottos as the usual sources.

Several of these suggestions come from Monash’s guide to Italian, Chinese, French and Indian dining. For a full plan, including what to say to staff, see eating out with IBS.

Here is the useful bit of food science: Monash explains that fructans dissolve in water but not in oil. When garlic or onion is warmed in oil, much of the flavor moves into the oil while the fructans stay in the solid pieces.

• At home: Monash’s method is to gently cook garlic pieces in oil for a minute or two, then discard the pieces and use the flavored oil.
• In stores: Products carrying the Monash University Low FODMAP Certified logo have been lab tested.
• Watch for pieces: An oil with chunks of garlic still in it, or a dish where garlic is cooked in and served, is not the same thing.
• Liquids carry fructans: Because fructans dissolve in water, a soup or stock simmered with onion keeps them even if the onion is strained out.

Monash’s list of low-FODMAP flavor ideas includes several onion and garlic stand-ins:

• Chives, which give a mild onion note.
• Spring onion (scallion), green part only. Monash lists the green part, not the white bulb.
• Asafoetida (hing), a pinch only, for an onion-like savory flavor. Powdered asafoetida is usually a blend, so read the ingredients, especially if you also avoid gluten (see hidden sources of gluten).
• Ginger, fresh herbs and citrus, which brighten a dish without relying on alliums.
• Garlic-infused or onion-infused oil, as above.

Serving sizes matter for FODMAPs, and even low-FODMAP foods can add up across a meal. The Monash FODMAP app has the current tested amounts. Our guide to FODMAP portion sizes explains why dose matters.

Not necessarily. The elimination phase of a low-FODMAP approach is meant to be short, and the challenge phase is there to find out what you actually tolerate. Tolerance varies from person to person, and the only way to know yours is to test it in a structured way.

1. Work with a doctor or registered dietitian to confirm that a low-FODMAP approach is right for you.
2. During elimination, focus on the hidden sources in this guide, not only whole garlic and onion.
3. In the challenge phase, test fructans in a structured way, ideally with a dietitian’s plan.
4. Keep a simple food and symptom diary so you can see your own patterns.
5. Bring back what you tolerate, and keep checking labels for the foods that still bother you.

If your symptoms change, get worse, or come with unexplained weight change, bleeding or fever, talk to your doctor rather than adjusting your eating on your own.