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.

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.

Imported recipes

Recipes brought in from other sites are re-weighed with the same rule. Their ingredient lines are converted to grams, anything high-FODMAP (onion, garlic, honey, wheat, most stocks, and so on) rejects the recipe outright, and anything the library cannot weigh rejects it too. "Portions trimmed" means the original recipe stacked past 0.85 and the vegetable portions were reduced until it didn't; the original page uses more than we show. We publish our per-plate weights and a link to the source, not the source's method text.

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 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.

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.