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How SI Gene Variants Affect Sugar Digestion and Digestive Symptoms

The SI gene makes the sucrase-isomaltase enzyme, which helps break down sucrose (table sugar) and certain starch fragments into simple sugars your body can absorb. Variations in SI can reduce enzyme activity, leaving more sugars in the small intestine to be fermented by gut bacteria. Fermentation can cause gas, bloating, abdominal pain, and other symptoms commonly addressed by a FODMAPs diet.

Why this matters

The standard FODMAPs diet limits certain fermentable carbohydrates such as wheat, onions, some fruits, and dairy. It does not specifically restrict sucrose or many refined starches. If your SI gene reduces sucrase-isomaltase activity, limiting typical FODMAPs may not fully relieve symptoms. Understanding your SI genotype can help you tailor a dietary and lifestyle approach that targets the specific carbohydrates that may be causing symptoms.

Genetic Interpretations

2 effect alleles (CC) — Reduced enzyme activity

Your CC genotype at rs147207752 is associated with reduced sucrase-isomaltase enzyme activity. This can make it harder to digest sucrose and some starch fragments. Undigested sugars can remain in the gut and be fermented by bacteria, producing gas, bloating, and abdominal discomfort.

What to consider

  • Limit added sugars and sugary beverages, including sodas, fruit juices with added sugar, candy, and desserts.
  • Reduce refined starches such as white bread, many pastries, and some processed snack foods. Choose whole grains cautiously and monitor tolerance.
  • Prefer smaller carbohydrate portions at meals to reduce the load on sucrase-isomaltase.
  • Consider targeted enzyme supplements that contain sucrase or combinations for carbohydrate digestion if recommended by a healthcare provider.
  • Eat slowly, chew thoroughly, and manage stress to support digestion.
  • Track symptoms and food intake to identify specific triggers and improvements.
1 effect allele (CT) — Moderately reduced enzyme activity

Your CT genotype at rs147207752 is associated with moderately reduced sucrase-isomaltase activity. You may digest sucrose and some starches less efficiently than average, which can lead to fermentation and symptoms similar to those seen with FODMAP intolerance.

What to consider

  • Moderate consumption of added sugars and sweetened beverages. Swap high sugar items for lower sugar alternatives when possible.
  • Limit refined starches and monitor portion sizes of carbohydrate-rich foods. Try pairing carbs with protein, fat, or fiber to slow digestion.
  • If symptoms persist after general dietary changes, consider a trial of enzyme supplementation with guidance from a clinician.
  • Practice lifestyle measures that support digestion, including mindful eating, regular physical activity, and stress management.
  • Keep a symptom and meal diary to help identify which foods or patterns worsen symptoms.
0 effect alleles (TT) — Typical enzyme activity

Your TT genotype at rs147207752 is associated with expected sucrase-isomaltase function. Sugars like sucrose and common starch fragments are likely broken down and absorbed normally. If you experience bloating or gas, those symptoms may be driven by other fermentable carbohydrates or unrelated causes.

What to consider

  • A standard FODMAPs approach can be appropriate for investigating persistent symptoms that suggest sensitivity to fermentable carbs like fructans, lactose, polyols, or fructose.
  • Maintain balanced carbohydrate intake and avoid excessive added sugars for general health and blood sugar control.
  • Use symptom tracking to help identify triggers and share findings with your healthcare team.

Dietary Recommendations

  • Limit added sugars and sugar-sweetened beverages. Focus on whole foods and use natural flavorings like herbs and spices.
  • Choose carbohydrate sources with more fiber and structure, such as whole fruits in moderation, legumes if tolerated, and minimally processed grains. Introduce these slowly and watch symptoms.
  • Prefer smaller, balanced meals combining carbohydrates with protein, healthy fats, and fiber to slow carbohydrate absorption and reduce fermentation risk.
  • If you follow a low FODMAP plan and still have symptoms, try a trial reduction in sucrose and refined starches while tracking effects.

Supplement and Testing Considerations

  • Enzyme supplements that include sucrase or broader carbohydrate-digesting enzyme blends may help symptom management for some people. Discuss options and dosing with your healthcare provider before starting.
  • Breath tests that measure hydrogen and methane can help identify carbohydrate malabsorption related to fermentation. Talk with a clinician about whether breath testing is appropriate for you.
  • Your clinician may recommend other tests if symptoms are severe or persistent, such as stool studies, nutrient assessments, or imaging, tailored to your history and exam.

Lifestyle Strategies to Support Digestion

  • Eat slowly and chew thoroughly to reduce the size of food particles and give your small intestine more time to work.
  • Manage stress using techniques such as deep breathing, meditation, gentle yoga, or regular physical activity. Stress can worsen digestive symptoms.
  • Stay hydrated, but avoid drinking large amounts of fluid during meals which can dilute digestive enzymes in some people.
  • Regular physical activity supports gut motility and overall digestive health.

How to Use This Information

Use your genotype information to guide focused changes in diet and habits. If you have reduced SI activity, target sucrose and refined starches in addition to the usual FODMAPs approach. Keep a food and symptom diary for several weeks to see patterns and share those findings with your healthcare provider or a registered dietitian. If you try enzyme supplements, coordinate with a clinician and evaluate benefits and any side effects.

When to See a Healthcare Provider

  • If symptoms are severe, persistent, or causing weight loss or nutritional problems.
  • If over-the-counter or lifestyle strategies do not improve symptoms after a reasonable trial.
  • If you are considering long term restriction of major food groups or starting new supplements, especially if you have other health conditions or take medications.

Important disclaimer

PlexusDx provides educational information about genetic predispositions only. This content is not medical advice. Always consult your healthcare provider or a registered dietitian before making significant changes to your diet, starting supplements, or pursuing diagnostic testing.