Low-FODMAP Macro Calculator for IBS & SIBO 🌎

What is the Low-FODMAP Diet?

Developed at Monash University (Australia) in 2005 by Dr. Peter Gibson and Dr. Susan Shepherd, low-FODMAP temporarily removes short-chain carbohydrates that gut bacteria rapidly ferment, producing gas, bloating, cramping, and pain. Clinical trials show 50–80% of IBS patients report meaningful symptom reduction during the elimination phase. For SIBO (Small Intestinal Bacterial Overgrowth), the diet reduces substrate available to misplaced bacteria, but it does not treat the underlying cause—antibiotic protocols remain the primary SIBO treatment.

> FODMAP stands for: Fermentable Oligo-, Di-, Monosaccharides And Polyols.

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The 5 FODMAP Groups to Restrict

Group	High-FODMAP Foods	Why It's Problematic
Fructans	Wheat, onion, garlic, leek	Most common IBS trigger; even small amounts matter
GOS (galacto-oligosaccharides)	Legumes, broccoli, beetroot	Humans lack the enzyme to digest them
Lactose	Milk, yogurt, ricotta	Only problematic in lactase deficiency—not everyone needs to cut it
Excess fructose	Apple, mango, honey, pear	Fructose absorbed poorly when it exceeds glucose in the same food
Polyols	Cherries, stone fruits, sorbitol (E420), xylitol	Slow, incomplete small-intestine absorption

Portion size matters critically. Many foods are low-FODMAP in small quantities but become high-FODMAP past a threshold—for example, ½ ripe banana is safe, a whole one is not. The official Monash FODMAP App provides tested portion thresholds.

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Allowed Low-FODMAP Foods

Category	Options
Grains	Rice, potato, quinoa, oats (½ cup cooked), polenta, gluten-free pasta
Protein	Chicken, beef, fish, eggs, firm tofu, canned tuna (in water)
Vegetables	Tomato, cucumber, carrot, spinach, zucchini, bell pepper, eggplant
Fruit	Strawberry, ripe banana (½), kiwi, orange, grapes, blueberries
Dairy	Lactose-free milk/yogurt, aged hard cheeses (cheddar, parmesan, brie)
Fats	Olive oil, avocado oil, small portion of avocado (⅛ whole fruit)

Aged cheeses are safe because the fermentation process breaks down lactose to negligible levels.

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How This Calculator Works

The calculator estimates your daily macronutrient targets within a low-FODMAP food framework using the following distribution:

Protein: 20% of total calories → grams = (kcal × 0.20) ÷ 4

Fat: 30% of total calories → grams = (kcal × 0.30) ÷ 9

Carbohydrates: 50% of total calories → grams = (kcal × 0.50) ÷ 4

These ratios are intentionally moderate—not ketogenic, not very high-carb—because both extremes can complicate FODMAP adherence. Very high-carb diets increase fermentation risk; very low-carb diets often rely on foods (nuts, avocado in large portions, certain vegetables) that can exceed FODMAP thresholds.

Reference macro table

Calories	Protein	Fat	Carbs
1,500 kcal	75 g	50 g	188 g
1,800 kcal	90 g	60 g	225 g
2,000 kcal	100 g	67 g	250 g
2,200 kcal	110 g	73 g	275 g
2,500 kcal	125 g	83 g	313 g

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The 3 Phases of the Monash Protocol

Phase 1 – Elimination (2–6 weeks)

Remove all high-FODMAP foods completely. Most patients see significant symptom relief within 1–2 weeks. Do not extend this phase beyond 6 weeks—prolonged restriction reduces gut microbiome diversity and is nutritionally incomplete long-term.

Phase 2 – Reintroduction (6–8 weeks)

Reintroduce one FODMAP group at a time (e.g., fructans in week 1, lactose in week 2), keeping a symptom diary. This identifies your specific triggers—most people tolerate 3–4 of the 5 groups without symptoms.

Phase 3 – Personalization (lifelong)

Resume a varied diet, avoiding only the specific groups confirmed as triggers. This phase is nutritionally sustainable and protects long-term microbiome health.

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What This Calculator Does NOT Include

Fiber targets – adequate fiber (25–38 g/day) is important but must come from low-FODMAP sources (oats, carrots, rice bran). This requires separate tracking.

Micronutrient gaps – eliminating legumes, wheat, and many fruits temporarily reduces calcium, iron, B vitamins, and folate. Consult a registered dietitian for supplementation guidance during Phase 1.

Calorie needs assessment – enter your own estimated TDEE; the calculator does not calculate it from height/weight/activity.

Medical diagnosis – IBS and SIBO require clinical diagnosis. This tool supports dietary management, not treatment.

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Common Mistakes

1. Using "gluten-free" as a synonym for "low-FODMAP." Gluten-free products can contain high-FODMAP ingredients like apple juice concentrate, honey, or inulin.
2. Ignoring cumulative load ("stacking"). Eating several low-FODMAP foods in the same meal can collectively exceed safe thresholds.
3. Skipping Phase 2. Staying in permanent elimination denies you the microbiome diversity your gut needs and makes the diet unnecessarily restrictive.
4. Assuming garlic-infused oil is high-FODMAP. Fructans are water-soluble, not fat-soluble—garlic-infused oil contains negligible FODMAPs and is safe.

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Always implement the low-FODMAP diet under guidance of a registered dietitian with GI specialization, particularly if you have a confirmed SIBO diagnosis or concurrent conditions such as Crohn's disease or celiac.