Congenital sucrase-isomaltase disease (CSID) is a digestive disorder caused by the inability to digest and absorb sucrose (table sugar) and isomaltase (a type of starch).

Consequently, sucrose and starch travel through your digestive system unchanged, causing a variety of uncomfortable and painful digestive symptoms.

Fortunately, you can prevent or relieve these symptoms by avoiding or limiting sucrose and starch in your diet.

This article explains what to eat and avoid with CSID and provides a sample CSID diet meal plan.

CSID diet

What is CSID?

CSID is a rare genetic condition caused by a mutation in the sucrase-isomaltase (SI) gene.

This mutation leads to a deficiency in the enzymes sucrase and isomaltase.

Normally, your small intestine secretes sucrase and isomaltase to break down sucrose and starch from the food you eat into smaller molecules so you can absorb them for energy.

However, without enough sucrase and isomaltase, sucrose and starch move through your small intestine undigested, causing various digestive symptoms.

Symptoms of CSID include (1):

  • stomach pain
  • diarrhea
  • excessive gas
  • bloating
  • reflux
  • loss of appetite
  • nausea
  • constipation
  • excessive burping
  • vomiting

CSID affects about 0.2–0.5% of the world’s population but its prevalence is much higher in native populations of Greenland, Canada, and Alaska (1).

CSID is present at birth but is often not diagnosed until solid foods containing sucrose or starch are introduced into the diet.

Sometimes, children are better able to tolerate starch around 3–4 years of age, but there’s limited evidence to show an improvement in sucrose tolerance with age.

Occasionally, CSID can go undiagnosed until adulthood (1).

Some people may develop a sucrase-isomaltase deficiency from inflammatory conditions that affect the small intestine like celiac disease and Chron’s disease (2).

Currently, the gold standard for diagnosing CSID is by taking a tissue sample of the small intestine and performing a test to determine enzyme activity levels (2).

CSID is generally not life-threatening or fatal, but it can cause malabsorption and lead to nutrient deficiencies, malnutrition, and failure to thrive in infants.

CSID diet

A CSID diet restricts foods with sucrose and starch since people with CSID lack the enzymes needed to completely digest and absorb them.

The level to which you have to restrict sucrose and starch from your diet to effectively relieve your symptoms will be specific to you.

To relieve your symptoms, you may have to follow an elimination diet under the guidance of a registered dietitian to determine your tolerability level of different foods.

It’s generally recommended to restrict both sucrose and starch for at least two weeks before reintroducing foods that contain sucrose and then starch back into the diet slowly and one at a time over several weeks.

Keep a food journal so you can track which foods you eliminate and what symptoms you experience — if any — after reintroducing them into your diet.

Foods to avoid or limit

Many people with CSID can tolerate some amounts of starch but not sucrose.

Examples of starches include barley, bran, bread, crackers, oats, pasta, quinoa, and rice.

Foods that are the least tolerated by people with CSID include (3):

  • Fruits: apples, apricots, bananas, cantaloupe, clementines, dates, gapefruit, guava, honeydew, mango, mandarin oranges, nectarines, oranges, peaches, and pineapples
  • Starchy vegetables: beets, butternut squash, carrots, cassava, and corn
  • Legumes: black beans, blackeyed peas, chickpeas, green peas, kidney beans, lima beans, navy beans, pinto beans, potatoes, and soybeans
  • Grains: bread, breakfast cereals, crackers, flavored oatmeal, granola bars, and pasta mixes
  • Dairy: flavored Greek yogurt, flavored milk, and dairy desserts
  • Processed meats: bacon, sausage, and lunch meat
  • Sweets and desserts: cake, chocolate, candy, ice cream, muffins, pie, etc.
  • Fats: almond butter and peanut butter
  • Condiments: barbecue sauce, honey, salad dressings, syrups,
  • Beverages: fruit juices, malt beer, sports drinks with sucrose, specialty coffee and tea drinks, regular soda and energy drinks

Foods to eat

People with CSID generally tolerate these foods:

  • Fruits: avocado, blackberries, blueberries, cherries, currants, grapes, kiwifruit, pears, pomegranates, prunes, raspberries, and strawberries
  • Vegetables: artichoke, arugula, asparagus, broccoli, brussels sprouts, cabbage, celery, cucumbers, kale, lettuce, mushrooms, spinach, tomatoes, onions, okra, sweet peppers, and zucchini
  • Dairy and dairy alternatives: butter, dairy milk, plain yogurt, cheese, cottage cheese, and unsweetened almond and soy milk
  • Beans, seeds, and legumes: kidney beans, pinto beans, pumpkin seeds, lentils, and lima beans
  • Poultry and eggs: fresh chicken, duck, goose, turkey, and eggs
  • Meats: fresh lean beef, lamb, and pork
  • Seafood: fresh fish, shrimp, crab, lobster, oysters, and scallops
  • Oils: canola and olive oil
  • Beverages: black coffee, unsweetened tea, water, and sucrose-free sports drinks

You can use fructose and dextrose to replace sucrose for cooking.

Spirits like whisky, vodka, tequila, and rum with sucrose-free mixers are fine in moderation if you are of legal drinking age.

One-day sample CSID diet menu

Here is a one-day sample CSID diet menu that is low in sucrose and starch:

Breakfast: Spinach-and-cheese omelet, blueberries, and milk

Snack: Plain Greek yogurt sweetened with dextrose and topped with sliced strawberries

Lunch: no-noodle lasagna with a tossed salad

Snack: cottage cheese and grapes

Supper: Grilled pork chop, steamed broccoli, and cherries

If you have trouble gaining weight, switch to full-fat versions of dairy products, choose fattier cuts of beef and fatty fish over their leaner counterparts, and add foods high in fat like avocado, butter, and olive oil to dishes.

Drinking sports drinks sweetened with fructose or dextrose can also help add calories without causing digestive symptoms.

Tips for managing CSID

Here are a few tips for managing CSID:

Chew your food thoroughly

Digestion — especially of starch — begins in your mouth.

Chewing breaks down food into smaller pieces and mixes it with saliva.

Saliva helps moisten and dissolve food but it also contains an enzyme that helps digest starch.

By chewing your food thoroughly, you increase the time saliva has to kickstart the digestion process.

Take a multivitamin

Depending on the severity of your symptoms, you may have to follow a very strict diet.

The more foods you eliminate, the greater risk you have of developing nutrient deficiencies.

Therefore, even with a well-balanced and carefully planned diet, you still may need to take a multivitamin supplement to ensure you’re getting enough nutrients.

Here are a few sucrose-free multivitamins based on age:

Read nutrition labels

Because so many foods naturally contain sucrose and starch or have them added during manufacturing, it can be difficult to know which foods to restrict or limit.

To determine whether a product contains sucrose or starch, you will need to read the ingredient list.

Ingredients are listed in order of predominance, with ingredients used in the greatest amount first, followed in descending order by those in smaller amounts.

Look for any ingredient that contains the word sugar, such as beet sugar, brown sugar, confectioner’s sugar, and cane sugar.

Maple syrup and molasses also contain a high content of sucrose.

Other names for starch to watch out for include dextrin, maltose, maltodextrin, isomaltose, and any ingredient that contains the word starch.

Enzyme replacement

In addition to your diet, you can also manage your symptoms with a medication called sacrosidase (Sucraide).

Sacrosidase is a powder that you can mix with a beverage other than fruit juice before and with meals and snacks.

This medication contains an enzyme derived from baker’s yeast that helps your body break down and absorb sucrose, preventing uncomfortable digestive symptoms and allowing for a more regular diet (4).

Talk with your doctor to see if sacrosidase is right for you, but remember that sacrosidase helps you digest sucrose, not starch.

The bottom line

CSID is a genetic disorder that prevents your body from completely digesting and absorbing sucrose and starch.

CSID affects people in different ways, and some people may be able to tolerate more sucrose or starch than others.

You can determine your tolerance level to sucrose and starch by completing an elimination diet under the guidance of a registered dietitian.


Gavin Van De Walle, MS, RD, LN
Gavin Van De Walle, MS, RD, LN

Gavin Van De Walle holds a master's degree in human nutrition and bioenergetics. He is a registered dietitian who aims to arm the public with evidence-based nutrition recommendations so they can make their own educated and informed health decisions.