What foods should you avoid on CSID?

January 3, 2026 •

3 min read

Congenital Sucrase-Isomaltase Deficiency (CSID) is a rare genetic disorder affecting an estimated 1 in 500 to 2,000 people of European descent. For those living with this condition, symptoms like diarrhea, bloating, and abdominal pain are triggered by the maldigestion of sucrose and starch. Knowing what foods should you avoid on CSID is the foundation of effective symptom management, as dietary modification is the primary treatment.

Quick Summary

A CSID-friendly diet restricts foods high in sucrose and certain starches, as the body lacks the necessary enzymes for proper digestion. Processed foods with added sugars and many grains and starchy vegetables should be avoided to prevent gastrointestinal symptoms.

Key Points

Sucrose is a Primary Trigger: Foods containing sucrose, including table sugar, many fruits, and certain vegetables, must be avoided due to the lack of the sucrase enzyme.
Starch Tolerance Varies: The maldigestion of starches is also a common issue for CSID patients, but individual tolerance levels differ. A guided elimination diet can help determine personal limits for grains and starchy vegetables.
Read Labels Carefully: Many processed foods, condiments, and packaged beverages contain hidden sucrose or starch-based fillers, so checking ingredient lists is essential.
Personalized Diet Plan: Working with a registered dietitian is crucial to create a personalized nutrition plan, especially for reintroducing foods and ensuring adequate nutrient intake.
Natural Proteins are Safe: Plain, unprocessed meats like chicken, beef, and fish, as well as eggs, are generally well-tolerated and form a core part of a CSID-friendly diet.
Unsweetened Dairy and Alternatives: Unflavored milk, unsweetened yogurt, and most hard cheeses are suitable, but sweetened or flavored dairy products should be avoided.
Consider Enzyme Replacement Therapy: For some individuals, prescription enzyme replacement therapy can help manage the digestion of sucrose, allowing for more dietary flexibility.

Understanding CSID and its Dietary Impact

Congenital Sucrase-Isomaltase Deficiency (CSID) is a condition where the small intestine lacks or has low levels of the enzymes sucrase and isomaltase. These enzymes are essential for breaking down sucrose (table sugar) and starches into simpler sugars for absorption. When undigested carbohydrates reach the large intestine, they are fermented by bacteria, leading to gas, bloating, diarrhea, and pain. The severity of the deficiency varies, meaning individual tolerance levels to sucrose and starches differ. Managing CSID symptoms primarily involves dietary modifications to limit the intake of trigger foods. A strict sucrose-free and low-starch diet is the starting point, often determined through an elimination diet under medical supervision.

Foods High in Sucrose to Avoid

Sucrose is not just found in table sugar; it's a component of many natural and processed foods. Careful label reading is essential to spot hidden sucrose under various names, such as brown sugar, maple syrup, and molasses.

Fruits High in Sucrose:

Apples
Apricots
Bananas
Cantaloupe
Dates
Mangoes
Oranges
Peaches
Pineapple

Vegetables High in Sucrose:

Carrots
Beets
Sweet potatoes
Onions
Parsnips

Common Processed Items with Added Sucrose:

Most sweetened beverages and fruit juices
Cakes, cookies, and other baked goods with added sugar
Many types of candy and ice cream
Sweetened yogurts and flavored milk
Certain condiments like barbecue sauce and ketchup

Starchy Foods Requiring Caution

Isomaltase is responsible for breaking down a significant portion of starches, so managing starch intake is also critical for CSID patients. Individual tolerance for starch varies widely, and many individuals find they can tolerate small amounts as they age. It is recommended to initially eliminate all starches during an elimination diet and then reintroduce them cautiously.

Grains and Grain Products:

Breads, pasta, and crackers made from refined flour
Breakfast cereals with added sugar
Quinoa, rice, and oats (tolerance can vary)

Starchy Vegetables and Legumes:

Potatoes (white and sweet)
Corn
Green peas
Legumes, including beans, lentils, and chickpeas

Processed Meats and Dairy with Additives

While plain, unprocessed meat and dairy are generally well-tolerated, many processed versions contain hidden sucrose or starch fillers that can trigger symptoms.

Processed Meats: Bacon, sausage, deli meat, and breaded meats often contain added sugar or starch.
Processed Cheese: American cheese slices and other processed cheese products frequently have starch fillers.
Flavored Dairy: Sweetened milks, yogurts, and ice cream contain sucrose.

Label Reading and Ingredient Recognition

Because sucrose and starch are ubiquitous in many products, becoming a savvy label reader is non-negotiable for anyone on a CSID-friendly diet. Ingredients to look out for include:

Sucrose terms: Sugar, cane sugar, brown sugar, molasses, maple syrup, date sugar, and beet sugar.
Starch-based fillers: Starches added to sauces, processed meats, and dairy.

Comparison of CSID-Friendly and Non-Friendly Foods


Food Category	CSID-Friendly Options	Foods to Avoid on CSID
Protein	Plain beef, chicken, fish, eggs, tofu	Breaded meats, processed sausage, deli meats, meatloaf
Dairy	Unsweetened yogurt, plain milk, hard cheeses	Flavored yogurt, ice cream, processed cheese
Fruits	Berries (strawberries, raspberries), lemons, limes, avocado	Apples, bananas, mangoes, cantaloupe, dried fruits with added sugar
Vegetables	Leafy greens (spinach, lettuce), cauliflower, cucumber, green beans	Corn, potatoes, carrots, sweet potatoes, peas, onions
Grains/Starches	Individual tolerance varies. Can test small amounts of whole grains, brown rice, rolled oats, quinoa	White bread, most pasta, crackers, breakfast cereals with added sugar
Sweeteners	Fructose, dextrose, honey (in small amounts), artificial sweeteners, Stevia	Table sugar, brown sugar, maple syrup, molasses, coconut sugar

Conclusion: Navigating a CSID-Friendly Diet

Living with CSID requires a thoughtful and disciplined approach to eating, centered on avoiding sucrose and adjusting starch intake based on personal tolerance. It is crucial to work with a healthcare professional, such as a registered dietitian, to create a personalized elimination diet plan. By being diligent with reading food labels, identifying hidden sugars and starches, and gradually reintroducing certain foods, individuals can find their unique tolerance levels. With the right knowledge and guidance, it is possible to effectively manage symptoms and improve overall quality of life while maintaining proper nutrition.

Sources

Frequently Asked Questions

Congenital Sucrase-Isomaltase Deficiency (CSID) is a genetic disorder where the small intestine has a reduced ability to produce the enzymes sucrase and isomaltase, which are needed to break down sucrose and starches. When these carbohydrates are undigested, they ferment in the large intestine, causing symptoms like diarrhea, gas, and cramping.

Fruits high in sucrose include apples, bananas, mangoes, cantaloupe, and citrus fruits like oranges and clementines. Fruits that are generally better tolerated often have lower sucrose content, such as berries (strawberries, raspberries), lemons, and limes.

Not all starches are equally intolerable. The isomaltase enzyme's role in starch digestion means that tolerance can vary significantly among individuals. Some people can handle small amounts of certain starches, while others cannot. An elimination diet is the best way to determine personal tolerance.

To find hidden sucrose, check the ingredient list for terms such as 'sugar,' 'brown sugar,' 'cane sugar,' 'maple syrup,' 'molasses,' and 'beet sugar.' Many processed foods, from sauces to cereals, contain these hidden sugars.

Plain, unprocessed protein sources are generally safe for individuals with CSID. This includes most beef, chicken, pork, lamb, and fish, as well as eggs. Avoid processed or breaded meats that often contain added starches or sugars.

Yes, many dairy products are tolerated if they are unsweetened and unflavored. Plain milk, hard cheeses, cottage cheese, and plain yogurt are typically safe. However, avoid sweetened milks, flavored yogurts, and processed cheeses with added starch fillers.

Enzyme replacement therapy, such as sacrosidase (Sucraid), can help break down sucrose and may allow for more flexibility in the diet. However, it does not aid in the digestion of starches, so dietary adjustments for starch intake may still be necessary, and therapy is often used in conjunction with dietary management.