Your genes and your microbiome are in constant conversation. Variants in genes like MTHFR, FUT2 and HNMT influence which microbes thrive in your gut and which symptoms appear when they don’t. Here’s how I interpret both together in clinic.

Why some digestive issues aren’t “just in your diet” — they might be in your DNA


By Kate Troup — Naturopath | Gut, Genes & Energy Specialist

Most people are told gut issues are caused by stress, food or hormones — and while that’s true for some, many people have a genetically sensitive gut that needs a more tailored approach.

In my clinic, I combine functional gut testing and genetic insights to help uncover why your gut reacts the way it does — so we can use targeted diet, lifestyle and supplement choices instead of random trial-and-error.

This guide introduces four key genes that influence gut function, tolerance to foods, microbiome balance, and inflammation.

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Overview: The Four Gut Genes

Gene Area It Influences Practical Impact
FUT2 (Secretor Gene) Microbiome foundation Prebiotic tolerance, microbial resilience, infection risk
SI (Sucrase-Isomaltase) Enzyme digestion Bloating from sugars/starches, IBS-like symptoms
TNFSF15 Immune & inflammatory response Gut sensitivity, IBD risk, stress-food flare-ups
AMY (Amylase genes) Starch digestion & metabolism Carb tolerance, bloating, energy dips

Gene 1: FUT2 — The Microbiome Gatekeeper

“The gene that decides which bacteria can live happily in your gut.”

What it does:

  • Determines whether your body “secretes” protective sugars called oligosaccharides into the gut.

  • These sugars act as food and welcome signals for beneficial gut bacteria.

  • Influences gut immunity and colonisation of healthy microbes like Bifidobacteria and Akkermensia.

If FUT2 is less active, you may:

  • React to garlic, onions, leeks, artichokes, legumes

  • Struggle with sudden increases in prebiotic fibre

  • Have more recurrent gut infections or overgrowths (e.g., SIBO, Candida)

  • Experience IBS-like symptoms without a clear trigger

Supportive Approaches:

  • Introduce prebiotic fibre slowly and strategically

  • Choose probiotics carefully—avoid “one-size-fits-all” formulas

  • Focus on gut barrier support (Vitamin A, zinc, glutamine, protein)

  • Consider microbiome testing before supplementing heavily

  • Consider supplementing with targeted prebiotic 2′-fucosyllactose (2′-FL) – also called HMO

Gene 2: Sucrase-Isomaltase (SI) — The Sugar & Starch Break-Down Gene

When sugars and starches aren’t broken down properly — they ferment in the gut, not feed your body.’

What it does:

  • Produces enzymes to digest sucrose (table sugar) and certain starches.

  • If less active, sugars and starches reach the colon undigested — leading to fermentation, gas and bloating.

Common Clues of SI Variants:

  • Bloated or crampy after fruit, juice, lollies, ice cream

  • IBS-like symptoms after bread, pasta, flour-based foods

  • Feel “6-months-pregnant” after desserts or starchy meals

  • Feel better on lower-carb or “whole food” meals

  • Symptoms improve when carbs are spaced out (not all at once)

Supportive Approaches:

  • Focus on slow carbs, lower sugar, whole food options

  • Pair carbs with protein/fat to ease blood sugar impact

  • Try small portions of starch rather than one big load

  • Enzyme support may help—but only if matched to your genes

Gene 3: TNFSF15 — Gut Inflammation & Immune Response

“Why some people’s guts overreact to stress, foods, or infections.”

What it does:

  • Regulates inflammatory responses in the gut.

  • Influences risk for IBS, IBD (Crohn’s, ulcerative colitis) in some.

  • Doesn’t cause disease but increases reactivity and sensitivity.


See this pattern often?

Red Flags

  • Flare-ups triggered by stress or certain foods

  • Gut reacts strongly to alcohol, NSAIDs, processed foods

  • History of “inflammation without infection”

Feels better with anti-inflammatory diet:

  • Symptoms swing between good and bad days

  • Sensitive to gut “irritant” foods

  • Feels better with anti-inflammatory diet

Supportive Approaches:

  • Load up on gut-calming foods: omega-3s, turmeric, leafy greens

  • Reduce inflammatory triggers (ultra-processed foods, excess alcohol, fried foods)

  • Support gut lining: collagen, glutamine, bone broth, zinc

  • Stress management = gut management

Gene 4: AMY (Amylase Genes) — Starch & Carbohydrate Tolerance

Why some people feel great on carbs — and others crash, bloat, or gain weight.

What it does:

  • Control how much amylase enzyme you make (mostly AMY1).

  • Amylase helps break down carbs and starches starting in the mouth.

You can have:

  • Higher AMY1 → good starch tolerance, but possible blood sugar swings

  • Lower AMY1 → more bloating, heaviness, energy dips after carbs

Low AMY1—Common Signs:

  • Feel heavy after rice/pasta/bread

  • Low energy a couple of hours after carb-heavy meals

  • Carbs “stick to your waistline” more

Helpful Strategies:

  • Balance each meal: Protein + Fat + Fibre + Carbs

  • Chew mindfully (carb digestion begins in the mouth)

  • Choose slow carbs: potatoes (with skin), oats, basmati rice, buckwheat

  • Pair carbs with cinnamon, protein or fibre to reduce spikes

Your Genes Are Not Your Destiny

Genes don’t dictate your future.

They simply explain your patterns — so you can make smarter choices.

Understanding your gut genes helps answer questions like:

  • “Why do certain healthy foods make me feel worse?”

  • “Why do I react when others don’t?”

  • “Why haven’t gut protocols, probiotics, or diets worked for me?”

Want to explore your genes?

This is exactly what I help clients with in my Gut & Genes consultations.

We look at your individual patterns — not just symptoms — through:

Targeted functional testing (gut, microbiome, enzyme function)

Comprehensive gene analysis (FUT2, SI, AMY, MTHFR, inflammation, detox)

Practical, personalised diet & supplement guidance

A step-by-step plan based on your biology — not Google

If you’d like to know how your gut really works

Book a consultation or request more information.

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