FodScale applies published low-FODMAP portion science mechanically. It is not medical advice and it is not a substitute for a dietitian. It cannot know your personal triggers, your tolerance, or whether you are in the elimination, reintroduction or personalisation phase of the diet. If you have IBS or another gut condition, work with a registered dietitian and use this site as a calculator, not a clinician.

The one rule

FODMAPs are six groups of fermentable sugars: fructose (in excess of glucose), lactose, sorbitol, mannitol, fructans and GOS (galacto-oligosaccharides). Symptoms come from the total of each group on the plate, not from any one ingredient, which is why "safe" ingredients can add up to an unsafe meal. That adding-up is called stacking.

For every ingredient in the library and every group it contains, there is a lab-tested safe portion in grams. A plate's load for a group is the sum, over its ingredients, of grams on the plate ÷ safe portion. FodScale accepts a plate only when every group's load is at or below 0.85. The clinical threshold is 1.0; the 15% gap is a deliberate buffer for kitchen measurement and lab variance.

That is the whole guarantee. When you see "Within limits" on a recipe, it means exactly this check passed for the per-plate weights shown.

What the gauge shows

Each bar is one of the six groups, from 0 to 100% of the clinical threshold, with a mark at 85%. Ingredients with no FODMAPs (plain meat, fish, eggs, tofu, rice, most oils) do not move any bar. Ingredients with a portion limit are marked • in the picker; the solver keeps them under it.

Stacking across groups: a person-by-person call

The rule above is applied to each group on its own, because each group misbehaves through its own mechanism: excess fructose overwhelms the gut's fructose transporter, polyols (sorbitol, mannitol) are absorbed slowly and draw in water, and fructans and GOS are not absorbed at all and are fermented. Monash's stacking guidance is framed the same way, as repeated servings within one group. So a plate at 80% fructose, 80% fructans and 80% sorbitol passes: three separate safe events.

Some people find that several busy groups on one plate add up anyway, because the gas and the water end up in the same gut at the same time. Others notice nothing. It is a person-by-person matter, and no test we know of settles it in advance, so the site reports it rather than ruling on it:

• A group is busy when it sits above half its ceiling.
• Recipes carry a 🧮 One busy group or 🧮 N busy groups badge; no badge means every group is light.
• The One busy group at most filter on the Recipes page keeps to plates where at most one group is busy, for anyone who has learned that stacking across groups bothers them.

The "Within limits" badge means the same thing either way: every group under 85% of its published portion. The busy-group note is extra information for you to weigh, not a second safety rule.

Recipes from other sites, and how we score them

Most of the library is recipes from established low-FODMAP sites, re-weighed with the same rule. Each one is credited and linked; we publish our per-plate weights and a pointer to the original method, never the source's text. Every card carries one of three labels:

• Verified as written. The recipe passed without a single change. It scores 100.
• Corrected: portions trimmed. The original stacked past 0.85 and one or more portions were reduced until it fit. The score is the share of the original's weight we kept unchanged, so a recipe trimmed by a tenth scores about 90.
• Corrected: ingredient swapped. Trimming alone could not save it, so a classic offender was replaced by its stand-in (garlic for garlic-infused oil, onion for spring-onion greens, honey for maple syrup, wheat pasta for gluten-free). A swapped recipe is never listed until a person has looked at it.

The changes are listed on every corrected recipe's page, with grams before and after. Anything the library cannot weigh, and anything with no safe stand-in, is rejected rather than guessed at.

Check a recipe

Paste any recipe URL on the front page and it goes through the same pipeline. You see the verdict immediately; if it passes, it waits in a review queue and joins the library once approved. Submissions are limited per connection to keep the queue honest.

How the generator decides

1. It fills a structural template (stir fry, sheet pan or grain bowl) from your protein and your list, using your picks first.
2. It starts every ingredient at a sensible default portion and adds up the six loads.
3. If any group is over 0.85, it scales that group's contributors down proportionally, never below a culinary minimum, and re-checks. If it still cannot get under, it swaps the heaviest contributor for something outside that group.
4. It multiplies the per-plate weights by your serving count for the shopping list.

Photos

Recipes carry the FODMAP gauge as their picture. Whoever saved a recipe can add one photo of their own dish; by uploading you confirm you took it yourself. Photos copied from other sites are removed.

Two optional gut lenses

Small-intestinal bacterial overgrowth comes in three breath-test flavours: hydrogen, methane (now called intestinal methanogen overgrowth) and hydrogen sulfide. All three gases start with microbes fermenting undigested carbohydrate, so the FODMAP rule above is the shared base. The generator and the recipe filters add two optional lenses on top. Neither changes the FODMAP calculation, and neither is a safety claim.

Fibre-forward. Methane slows gut transit, so the picture is constipation, and a naive low-FODMAP diet often makes it worse by dropping fibre. This lens steers the solver toward safe, fibre-carrying ingredients (oats, chia, kiwi, firm banana, carrots, sweet potato, canned lentils, leafy greens) and tags recipes with two or more of them.

Lower sulfur. Hydrogen-sulfide overgrowth is the newest and least settled type. The proposed dietary lever is reducing sulfate and sulfur amino acid sources: cruciferous vegetables, alliums (including garlic-infused oil, whose flavour compounds are sulfur-based), eggs, dairy, red meat and sulfited wine. Poultry, fish and tofu stay. The evidence is case series from one research group, not trials, so treat this lens as a reasonable hypothesis you and your clinician can test, not established practice.

Diet manages symptoms in all three types; it is not the treatment, which is antimicrobial and, for methane, motility-focused. Long-term restriction starves the helpful microbiome too, so the standard path is test, treat, restrict briefly, reintroduce.

Spice is a preference, not a criterion

Chili, black pepper, ginger and nearly every dried spice contain no fermentable carbohydrate, so heat never affects any bar. The exceptions are onion and garlic powders and blends that contain them, which the importer swaps or rejects. Capsaicin can still irritate a sensitive gut through a different mechanism, so heat is offered as a personal setting on the generator and as a tag you can filter out. It is your call, not the calculator's.

What this site does not know

• Your individual tolerance. The portion limits are population-level lab values.
• Whether you should be restricting at all. The low-FODMAP diet is a short-term diagnostic tool, not a lifestyle.
• Brand-level formulation. A sauce that is fine in principle can contain onion in practice; read labels.

Your data

There are no accounts. A random ID minted in your browser is your identity for saving, tweaking and reviewing; it lives on this device only. "Save my data" in the header will let you carry it to another device in a later release.

Sources

Portion thresholds follow the values published by Monash University's FODMAP research program, which originated the diet and maintains the reference database (monashfodmap.com), interpreted conservatively where figures have changed between app releases. The stacking arithmetic and the 0.85 buffer are this site's own.