Why Diet Matters in SIBO

Small Intestinal Bacterial Overgrowth is fundamentally a problem of bacteria being in the wrong place. These bacteria ferment the food you eat, producing gas and toxic byproducts that cause bloating, pain, diarrhoea, or constipation. The dietary strategy in SIBO is therefore twofold: reduce the substrates that overgrown bacteria feed on, and support the body's own ability to clear the overgrowth.

It is important to understand that diet alone rarely eradicates SIBO. However, the right dietary approach significantly reduces symptoms during treatment, improves the efficacy of antimicrobial therapy, and helps prevent recurrence.

Foods to Eat During SIBO Treatment

Proteins

Protein is your safest macronutrient during SIBO treatment because bacteria primarily ferment carbohydrates, not protein.

  • Wild-caught fish (salmon, cod, sardines, sole)
  • Pasture-raised poultry (chicken, turkey)
  • Grass-fed beef and lamb
  • Eggs (a versatile, easily digestible protein source)
  • Bone broth (provides protein plus gut-healing glycine and collagen)

Low-FODMAP Vegetables (Well-Cooked)

Cooking breaks down fibre and makes vegetables easier to digest, reducing fermentation in the small intestine:

  • Zucchini and summer squash
  • Carrots (cooked)
  • Spinach and bok choy
  • Bell peppers
  • Cucumber (peeled and seeded)
  • Green beans (in small amounts)
  • Lettuce and arugula (for salads)

Healthy Fats

Fats are not fermented by bacteria and provide essential calories and nutrients:

  • Extra-virgin olive oil
  • Coconut oil (contains lauric acid with mild antimicrobial properties)
  • Avocado (small servings — large amounts contain polyols)
  • Ghee (clarified butter, usually tolerated even with dairy sensitivity)
  • Olives

Low-FODMAP Fruits (In Moderation)

  • Blueberries, strawberries, and raspberries (small servings)
  • Citrus fruits: oranges, lemons, limes
  • Kiwi fruit
  • Unripe banana (small amounts)
During active SIBO treatment, even "safe" foods should be eaten in moderate portions. The goal is to minimise the total fermentable load reaching the small intestine at any given time.

Foods to Avoid During SIBO Treatment

High-FODMAP Foods

These are the primary substrates for bacterial fermentation in the small intestine:

  • Garlic and onion — the most common triggers; high in fructans
  • Wheat, rye, and barley — contain fructans (the SIBO issue with wheat is the fructans, not gluten per se)
  • Legumes (beans, lentils, chickpeas) — high in GOS (galacto-oligosaccharides)
  • Apples, pears, mangoes, watermelon — high in excess fructose
  • Milk and soft cheeses — high in lactose
  • Cauliflower, mushrooms, stone fruits — high in polyols

Sugar and Refined Carbohydrates

Simple sugars are rapidly fermented by overgrown bacteria:

  • Table sugar, honey, agave, maple syrup
  • Soft drinks and fruit juices
  • White bread, pastries, and baked goods
  • Candy and confectionery

Alcohol

Alcohol increases intestinal permeability, disrupts the microbiome, and impairs the migrating motor complex. It should be avoided entirely during SIBO treatment and minimised during recovery.

Artificial Sweeteners

Sorbitol, mannitol, xylitol (polyols), and sucralose all either serve as bacterial substrates or disrupt the microbiome. Stevia in small amounts is generally tolerated.

Meal Timing and Structure

How you eat is as important as what you eat in SIBO management:

  • Three meals per day with no snacking — this allows 4-5 hour gaps between meals for the MMC to activate and sweep bacteria from the small intestine
  • 12-14 hour overnight fast — from dinner to breakfast, giving the MMC maximum overnight clearance time
  • Eat slowly and chew thoroughly — mechanical digestion reduces the particle size that reaches the small intestine, reducing fermentation
  • Moderate portion sizes — smaller meals reduce the total fermentable load at any given time

After SIBO Treatment: Reintroduction

Once SIBO has been eradicated (confirmed by a follow-up breath test), the dietary strategy shifts from restriction to gradual reintroduction and diversity building:

  • Reintroduce one high-FODMAP food group every 3-4 days
  • Start with small portions and increase gradually
  • Track symptoms carefully during reintroduction using a food diary or GutIQ
  • Maintain meal spacing habits long-term to support ongoing MMC function
  • Gradually increase prebiotic fibre to rebuild microbial diversity

The long-term goal is the least restrictive diet that maintains symptom control. Permanent dietary restriction is neither necessary nor desirable for most successfully treated SIBO patients.