Is garlic low FODMAP? Onion, garlic and the infused oil trick

Garlic and onion are particularly high in fructans, which makes them difficult to include during the elimination phase of the low FODMAP diet. The good news is that there is a real trick here, one that lets you keep most of the flavour. It comes down to a single piece of chemistry.

Why garlic and onion are high FODMAP

The problem is fructans, one of the oligosaccharides in the FODMAP family. Humans lack the digestive enzymes needed to fully break down fructans in the small intestine. They therefore reach the large intestine, where they are fermented by gut bacteria. In some people with IBS, this can contribute to symptoms such as gas, bloating and abdominal discomfort. Our guide to the FODMAP families covers the rest of the acronym.

Garlic and onion are unusually concentrated in fructans, which is why Monash University's published research rates them high even at very small serves. This is why garlic and onion are generally avoided during the elimination phase of the low FODMAP diet.

The trick: fructans dissolve in water, not in oil

Here's the useful part: fructans are water soluble, but not oil soluble. They move into anything watery and they stay put in anything fatty.

Two consequences follow, and they run in opposite directions.

Drop a garlic clove into hot oil and the aromatic compounds, which are oil soluble, move into the oil. The fructans do not. Take the garlic out and you are left with garlic flavoured oil that is low FODMAP. This is why garlic infused oil is one of the few genuine wins on this diet.

Now drop that same clove into a pot of stock, a simmering sauce or a marinade. The fructans leach straight into the liquid, and the liquid is the part you eat. Fishing the garlic out at the end changes nothing.

Two things people get wrong:

• Frying garlic and leaving it in. The pieces still hold their fructans, and you swallow them. Infuse the oil with whole garlic cloves or large pieces, then remove and discard them before adding the other ingredients.
• Garlic powder, garlic salt, onion powder and onion granules still contain the fructans found in the original ingredient, so they are not equivalent to infused oil.

What you can use instead

Based on Monash University's public research, these keep a savoury base going:

• Garlic infused oil, shop bought or home made, with no solid pieces left in
• Spring onions, green tops only, since the fructans sit in the white bulb
• Leeks, using the green leaves at a low FODMAP serving size
• Chives, which are low FODMAP in normal cooking amounts
• Asafoetida, also sold as hing, a pinch of which gives a remarkably onion like note. Check the label: it is often cut with wheat flour, which matters if you are coeliac

Where garlic and onion hide on labels

Watch for "spices", "seasoning", "natural flavours", "flavouring", "vegetable powder", stock, bouillon and yeast extract blends.

The usual suspects in a supermarket trolley: stock cubes and gravy granules, marinades and rubs, crisps and savoury snacks, pasta sauces and ketchup style condiments, sausages and cured meats, and a lot of ready meals. Our aisle guides go through what tends to be safe in sauces, ready meals and snacks.

Belly Buddy exists partly for this problem: scan the ingredient list and it flags garlic and onion wherever they turn up. You can read how we rate a product. We are not affiliated with Monash University.

Flavour without the fructans

A savoury dish does not actually need garlic and onion, it needs depth. Build it from somewhere else:

• Garlic infused oil as the fat you start the pan with
• Ginger, grated fresh, for warmth
• Lemon zest and juice to lift a sauce that tastes flat
• Smoked paprika for extra depth
• Cumin, coriander seed and fennel seed, toasted for a minute
• Fresh herbs in quantity, thyme and rosemary while cooking, parsley and basil at the end
• Miso, in small amounts, for savoury weight

And remember that elimination is a temporary phase: when you reach reintroduction, fructans get tested like every other group, ideally with a FODMAP trained dietitian, and plenty of people find they tolerate more than they feared.

Sources

• Monash University FODMAP research