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Understanding sucrase-isomaltase (SI) and how it affects digestion

The SI gene makes the sucrase-isomaltase enzyme. This enzyme helps break down sucrose (table sugar) and certain starches into simpler sugars that your small intestine can absorb. When SI function is reduced, sucrose and rapidly digestible starches may remain undigested in the small intestine and then ferment in the large intestine. That fermentation can cause bloating, gas, pain, and other symptoms that often resemble those addressed by a FODMAPs diet.

How this relates to the FODMAPs diet

The FODMAPs diet reduces specific fermentable carbohydrates such as fermentable oligosaccharides, disaccharides (like lactose), monosaccharides (like excess fructose), and polyols. The standard low FODMAP approach does not specifically limit sucrose or many rapidly digestible processed starches. If your SI enzyme activity is reduced, limiting typical FODMAP foods may help some symptoms, but undigested sucrose and starches can continue to trigger fermentation and discomfort unless they are also addressed.

Common symptoms associated with reduced SI activity

  • Bloating and visible distention
  • Excessive gas or flatulence
  • Abdominal pain or cramping
  • Loose stools or alternating diarrhea and constipation
  • Symptoms that worsen after consuming sweets, sugary drinks, or processed starchy foods

Practical dietary and lifestyle recommendations

Below are approachable, actionable strategies to consider if you or your healthcare provider suspect reduced SI function. These suggestions can be personalized with the help of a registered dietitian and your healthcare provider.

Dietary strategies

  • Limit high-sucrose foods and beverages: reduce table sugar, candies, sweetened drinks, desserts, and syrups.
  • Choose whole-food carbohydrate sources: favor intact grains, legumes, vegetables, and fruits lower in free sugars rather than processed starches and refined flours.
  • Be mindful of processed starches: many processed foods contain rapidly digestible starches that can behave like sucrose when SI activity is low. Read labels and reduce highly processed breads, pastries, and snack foods if they trigger symptoms.
  • Eat smaller, more frequent meals: smaller portions reduce the carbohydrate load in a single sitting and may improve digestion and reduce fermentation.
  • Chew thoroughly and eat slowly: mechanical breakdown supports enzyme action and reduces the chance of large carbohydrate boluses reaching the large intestine undigested.
  • Consider targeted carbohydrate testing: under guidance, short elimination and reintroduction trials of sucrose and high-starch processed foods can identify triggers.

Supplements and digestive aids

  • Sucrase-containing enzyme supplements: prescription or over-the-counter enzyme products containing sucrase or broad-spectrum carbohydrases can help break down sucrose and starches. Use only under healthcare guidance.
  • Probiotics: some people find symptom relief with certain probiotic strains, though results vary. Discuss options with a clinician.
  • Avoid indiscriminate use of digestive supplements: not all products are studied for SI-related issues; coordinate use with your provider.

Lifestyle and monitoring

  • Keep a food and symptom journal: record foods, portion sizes, timing, and symptoms to identify patterns and triggers.
  • Hydration and physical activity: staying hydrated and keeping active can support normal gut motility and digestion.
  • Work with a dietitian: a registered dietitian familiar with carbohydrate disorders and FODMAPs can help tailor a plan that minimizes nutrient gaps.
  • Consider diagnostic testing: your clinician may recommend breath tests, stool or genetic testing, or referral to a gastroenterologist if symptoms are persistent or severe.

Genetic interpretation for rs146785675

GG genotype — two effect alleles

You carry two copies of the effect allele at rs146785675. This genotype is associated with reduced sucrase-isomaltase enzyme activity. With weaker SI function, sucrose and some rapidly digestible starches may not be fully broken down in the small intestine and can reach the large intestine where they ferment, producing gas, bloating, and discomfort.

Practical steps to consider:

  • Limit high-sucrose foods and sweetened beverages.
  • Reduce intake of highly processed starches; choose whole-food carbohydrate sources.
  • Discuss sucrase-containing enzyme replacement or broad-spectrum carbohydrase supplements with your healthcare provider.
  • Eat smaller meals and chew thoroughly to reduce carbohydrate overload per meal.
  • Track food and symptoms to tailor your plan and identify specific triggers.
AG genotype — one effect allele

You carry one copy of the effect allele at rs146785675. This genotype is associated with a partial reduction in sucrase-isomaltase activity for some people. You may experience digestive symptoms similar to those seen in reduced SI function, especially after consuming sugary foods or processed starches.

Practical steps to consider:

  • Monitor and modestly limit foods high in sucrose and highly processed starches to see if symptoms improve.
  • Try smaller, more frequent meals and thorough chewing to ease digestive strain.
  • Consider a brief trial of sucrase-containing enzyme supplements under medical guidance if symptoms persist.
  • Keep a detailed food and symptom journal to determine whether sucrose or certain starches are meaningful triggers for you.
AA genotype — zero effect alleles

You carry two copies of the non-effect allele at rs146785675. This genotype is associated with typical sucrase-isomaltase enzyme activity. Your SI enzyme is expected to break down sucrose and starch-derived carbohydrates effectively in the small intestine, so undigested sucrose-related fermentation is less likely to be the primary cause of symptoms.

Practical steps to consider:

  • If you have IBS-like symptoms, a low FODMAPs diet may be a suitable first-line dietary approach because sucrose and starch digestion is likely not the main issue.
  • Track foods and symptoms to identify other potential triggers such as lactose, fructans, or polyols.
  • Work with a clinician or dietitian to pursue targeted testing or trials if symptoms persist despite standard dietary changes.

When to seek professional care

Contact your healthcare provider if you have persistent abdominal pain, significant changes in bowel habits, unexplained weight loss, blood in the stool, or if symptoms interfere with daily life. A clinician can order tests, review medications, evaluate for other causes, and help design a safe, individualized plan.

Final notes and disclaimer

PlexusDx provides educational information about genetic predispositions and possible lifestyle and dietary approaches. This content is not medical advice. Always consult your healthcare provider before making changes to your diet, starting supplements, or pursuing testing. Your provider can help interpret genetic results in the context of your symptoms, medical history, and clinical testing.