Nearly every jar of pasta sauce on the shelf starts the same way: olive oil, then garlic, then onion. That is not a flaw. It is the recipe, and it is four hundred years old. But those two ingredients sit near the top of every published list of high-fructan foods, and fructans are the one carbohydrate no human being digests. If sauce sits badly with you and you have been blaming the tomatoes, the second and third ingredients are worth a look.
Two different things in one jar
They come from different ingredients, they behave differently, and they are usually confused for each other
Associated with reflux and burning. Felt high, and usually soon after eating. This is the one most people already know about.
A carbohydrate nobody digests. Fermented lower down, hours later. Garlic and onion are the largest dietary sources measured.
Removing one does nothing about the other. They are not the same complaint.
What is on this page
- The ingredient nobody reads past
- Garlic and onion sit at the top of every measured list
- Fructans dissolve in water, and that changes everything
- Why picking the pieces out does not work
- Oil behaves differently, and that is not a loophole
- So what do you actually do about it
- What this does not mean about tomatoes
- Acid and fructans are two different complaints
- What is in my jar, and what I have never measured
- Questions people ask me about this
The ingredient nobody reads past
Pick up a jar of sauce and read the list. Tomatoes first, almost always. Then oil. Then, in most of them, garlic and onion, sometimes both, sometimes as powder, sometimes hiding inside the words "spices" or "natural flavors."
People read that list looking for sugar. They read it looking for citric acid. I have watched customers at markets run a finger down a label hunting for the thing they think is doing it, and I have almost never seen anyone stop at the garlic.
I want to be careful here, because I sell a sauce that has neither, so you should assume I have a reason to point at them. What I can do is show you the measurements and the mechanism, and let you decide whether they explain anything about your own week.
Reading for them is harder than it sounds, because they are rarely printed as one clean word. Onion and garlic appear on labels in at least eight forms, and two of those are not words at all.
What garlic and onion are called on a label
Same two plants, eight ways of writing them, and two that do not name them at all
Garlic. Onion. Red onion, white onion, yellow onion, shallot, leek.
Garlic powder, onion powder, granulated garlic, dehydrated onion, minced dried garlic.
Spices. Natural flavors. Seasoning blend. Soffritto. Mirepoix. Vegetable base.
Drying takes out the water, not the fructan. Per gram, the powder is the more concentrated form, not the gentler one.
The short version: garlic and onion are not incidental seasonings from a digestion point of view. In the food composition literature they are among the heaviest sources of a carbohydrate called fructan that is present in almost everybody's diet and absorbed by almost nobody.
Garlic and onion sit at the top of every measured list
In 2007 a group at Monash University measured total fructans across sixty vegetables and forty-three fruits. Their conclusion names the winners directly: the vegetables with the highest quantity of fructans were garlic, artichoke, shallots, leek bulb, and onions, across a range of 1.2 to 17.4 grams per 100 grams of fresh weight (Muir et al., Journal of Agricultural and Food Chemistry, 2007;55(16):6619-6627).
That is a wide range, and it is a range for the group, not a figure for any one of them. I am not going to turn it into a precise number for garlic, because that paper reports it as a band and I would be inventing precision that is not there.
A more recent Slovenian analysis measured individual foods with a single consistent assay and put onion at 1.97 grams per 100 grams. In the same study, cooked pasta came in at 0.33 and white bread at 0.14 (Ferjančič et al., Frontiers in Nutrition, 2024;11:1446771). By weight, the onion is carrying about six times what the pasta underneath it is carrying.
The same paper estimated that average daily fructan intake runs between 1.6 and 1.7 grams a day. Hold onto that number, because it makes the next one land properly.
In a blinded Norwegian trial, fifty-nine people who were certain gluten was their problem were given concealed bars containing gluten, fructan, or a placebo for seven days each. The fructan dose was 2.1 grams a day. On bloating, fructan scored 11.6, placebo 10.1, and gluten 9.3 (Skodje et al., Gastroenterology, 2018;154(3):529-539). Just over one ordinary day's worth of fructan, given deliberately, was enough to move the score. I wrote up that trial and five other explanations in what a fructan is, and the trial that separated it from gluten.
These findings come from independent research and do not guarantee the same results with our product.
Fructans dissolve in water, and that changes everything
Here is the part that took me a while to understand, and it is the most useful thing on this page.
Fructans are water soluble. Monash puts it plainly: the fructan content in onion and garlic is soluble in water. Put either one into a liquid and the fructans come out of the vegetable and go into the liquid.
A pasta sauce is a liquid. It simmers for an hour, sometimes longer. Whatever fructan was in the garlic and the onion at the start of that hour is, by the end of it, distributed through the sauce.
This is not a criticism of anybody's recipe. It is what a soffritto is designed to do. You sweat the aromatics in fat and then you introduce the tomatoes precisely so their flavour goes everywhere. The flavour compounds and the fructans travel by the same route, and the process cannot separate them.
Why picking the pieces out does not work
The most common thing people try is to cook with a whole clove or a halved onion and then fish it out before serving. It feels like it should work. It is intuitive. It does not do what people think.
Monash addresses this one directly, and I will quote it rather than paraphrase, because it is the single most misunderstood point in this whole subject: the strategy of putting a whole onion or garlic clove into a soup and then pulling the pieces out before consuming the soup will not work, as the fructan content will have already leached into the water.
The pieces are not where the problem is by the time you remove them. The pieces are just what is left over after the transfer.
Same for straining. Same for a sauce that looks perfectly smooth and lists no visible allium. Smooth is a texture, not an ingredient list. If garlic and onion went into the pot with water present, they are in the jar whether or not you can see them.
These findings come from independent research and do not guarantee the same results with our product.
Oil behaves differently, and that is not a loophole
The mirror image of that rule is the useful one. Monash again: in an oil based dish the fructans will not leach out, as fructans are not soluble in oil.
This is the reason infused olive oil exists as a category. The aromatic compounds that make garlic smell like garlic are happy to move into fat. The fructans are not. So the oil ends up carrying the flavour and leaving the carbohydrate behind in the solids, which then get removed.
I want to be honest about the limit of this, because it gets oversold. Infused oil is not a magic trick that makes garlic disappear from a recipe. It works because the transfer never happens, so the timing and the water content matter. The moment there is water in the pan with the garlic solids still in it, you are back to the first rule.
It is also worth saying that none of this is about whether garlic and onion are good food. They are good food. Most people eat them daily with no trouble at all, and the fructans in them feed gut bacteria in ways researchers are genuinely interested in. This page is about a specific mechanism in specific people, not a case against the allium family.
So what do you actually do about it
Everything above is mechanism. Here is the part that changes what happens at your stove, and it comes down to one thing: the fructans move when the water arrives, so the question is only whether the garlic is still in the pan at that moment.
A soffritto already gives you the opening. The first stage is oil and aromatics with no water in the pan yet. That stage is doing the flavour work. The transfer you do not want has not happened yet, because it cannot.
If you cook your own sauce
The order of operations is the whole technique. Nothing here is a special ingredient.
A halved clove and a quartered onion. You are after flavour in the oil, and you want to be able to find them again.
Warm them gently in the olive oil. This is the stage where the aroma moves into the fat and the fructans do not.
Remove the pieces before anything wet goes in. Once the tomatoes are in the pan, it is too late.
Monash suggests the same idea in bottled form: make a garlic infused olive oil and cook with that instead of your regular oil.
That is the honest version of the trick, and I want to name its limits rather than let you find them. It only works while the pan is dry. If you mince the garlic so fine you cannot retrieve it, you have not done this. If you add it back at the end for freshness, you have undone it. And if the recipe calls for the onion to soften into the sauce and stay there, which many good recipes do, then this technique is simply not available and you should cook the recipe properly instead.
If you want it written out as an actual method, my Sicilian soffritto is the base I cook from, and there is a sofrito version aimed at reducing acidity as well.
If you buy your sauce instead, the job is smaller and it is all on the label. Read past the tomatoes. Garlic and onion are frequently there in powdered form, or inside "spices" and "natural flavors," and a sauce being perfectly smooth tells you about a sieve, not an ingredient list. If those words are on the jar, the fructans went into it during cooking and they did not come back out.
And one worth knowing because it catches people: a whole onion simmered in a soup or a stock and then lifted out has already done the transfer. That is the exact case Monash uses. If you have been making onion soup and fishing the pieces out, the fructans stayed in the bowl.
These findings come from independent research and do not guarantee the same results with our product.
What this does not mean about tomatoes
I could stop here and let you conclude that the tomatoes are innocent. That would be convenient for me and it would not be true.
Tomatoes carry fructose. Fructose is a different FODMAP from fructan, and it has its own thresholds. Monash's tested serving sizes put common tomato in the low range at about 65 grams, roughly half a medium tomato, and moving into moderate for fructose at around 75 grams. For cherry tomatoes the low range runs to about 45 grams, three medium ones, with 60 grams tipping into moderate.
Read those numbers against a bowl of pasta. Nobody eats three cherry tomatoes' worth of sauce.
So here is the honest shape of it. Taking garlic and onion out of a sauce removes the fructan contribution from the aromatics. It does not remove the fructose that came in with the fruit, and it does not turn a jar of concentrated tomatoes into a low FODMAP food. Those are two separate ledgers and I am only telling you about one of them.
My sauce is not a low FODMAP product and I am not going to call it one. That is a term with a certification behind it, my sauce does not carry that certification, and the tomato thresholds above are the reason I would not expect it to. What I can tell you is which ingredients are in the jar.
Acid and fructans are two different complaints
Most of what I get asked about sauce is about acid. That is a real and separate thing, and it has its own mechanism: reflux, burning, felt high in the chest, usually not long after a meal. If that is your description, the fructan story on this page is probably not yours, and I have written about why tomato sauce causes heartburn for some people and about a low acid sauce and what that actually means separately.
The fructan description is different. It tends to be lower down, it tends to be gas and distension rather than burning, and it tends to arrive later, because fermentation takes hours and has to wait until the carbohydrate reaches the colon.
Two different molecules, two different parts of the body, two different clocks. People arrive assuming they have one problem with their sauce. Sometimes they have two, and sometimes the one they have been working on is not the one they actually have.
I am not diagnosing anybody. I am a person who makes sauce, and the reason I bothered to learn the difference is that customers kept describing two clearly different experiences to me using the same three words.
What is in my jar, and what I have never measured
My sauce has four ingredients, and I will give them in the order they are printed on the back: red cherry tomatoes, basil, extra virgin olive oil, sea salt. No garlic. No onion. Not as powder, not inside "spices," not anywhere.
I would love to tell you that was a brilliant piece of food science. It was not. My mother made it that way, in Santa Ninfa, because good cherry tomatoes in July do not need help and she thought garlic buried the fruit. I only found out later that the choice had a second consequence.
Now the part I have to say plainly. Nobody has ever measured the fructan or FODMAP content of my sauce. Not a lab, not me. The reports I publish for my pasta do not contain a fructan number either, and I wrote about exactly what the lab measured in my pasta and what it did not. What I have here is an ingredient list, not an assay.
So the honest sentence is this one: the two foods that the published literature ranks highest for fructans are not in the jar, and I can show you the label that proves it. Whether that matters for you is something only you can find out, and I would rather hand you the mechanism and the label than a promise.
If you want the version you cook yourself rather than the version I sell, I published a sauce built without the aromatics as a recipe. It costs you nothing and it tells you the same thing.
Questions people ask me about this
Are garlic and onion high in fructans?
Yes. In a Monash analysis of sixty vegetables, garlic, artichoke, shallots, leek bulb, and onions were the highest fructan group measured, in a range of 1.2 to 17.4 grams per 100 grams fresh weight. A separate study measured onion at 1.97 grams per 100 grams, about six times the level in cooked pasta.
Can I just remove the garlic and onion pieces after cooking?
Not if there was water in the pan. Fructans are water soluble, so they leach into the liquid during cooking and stay there after the solids are removed. Monash states directly that this strategy will not work for a soup or stock.
Why is garlic-infused oil different?
Fructans do not dissolve in oil. The flavour compounds move into the fat and the fructans stay in the solids, which are then strained out. The separation only holds while water is absent.
Is your sauce low FODMAP?
No, and I will not call it that. Low FODMAP is a certification term and my sauce does not carry it. Cherry tomatoes move into the moderate range for fructose at around 60 grams, which is far less than a serving of sauce. What is true is narrower: there is no garlic and no onion in the jar, so there is no fructan contribution from the aromatics.
Is it the acid or the fructans?
They are separate. Acid is associated with burning and reflux, usually felt high and soon after eating. Fructans are fermented in the colon, so the timing is later and the description is closer to gas and distension. Some people have one, some have both.
Have you had the sauce tested for FODMAPs?
No. There is no fructan or FODMAP assay on my sauce or on my pasta. Everything on this page about my product comes from the ingredient list, and everything about fructans comes from published research on those ingredients generally.
Do fructans affect everybody?
Nobody digests them: humans do not make the enzyme, so they reach the colon intact in every person. What differs is the dose at which that becomes something you notice. That is why the same food can be fine one day and not the next.
These findings come from independent research and do not guarantee the same results with our product.
Disclaimer: the content in this blog is for informational purposes only and should not be taken as professional, medical advice.
You know what to look for on the back of a jar now. Mine puts the answer on the front: No Onion, No Garlic, No Added Sugar, with four ingredients behind it. Red cherry tomatoes from my parents' valley, basil, my own olive oil, sea salt. I am not promising you anything about how you will feel. I am telling you what is in the bottle and inviting you to check.
See the sauceI'm not a doctor. This is my food and my story. Talk to your doctor, and read your labels.
