A reliable diagnosis can only be obtained through a biopsy of the small intestine. This can determine the sucrase-isomaltase activity in the tissue of the small intestine. It is also possible to perform a hydrogen breath test.
The diet consists of eating foods that are low in sucrose. Sucrose, also known as granulated or household sugar, a disaccharide, is largely replaced by glucose (dextrose), fructose (fruit sugar) and lactose (milk sugar).
Look out for some fruits because they quite often contain high levels of sucrose.
Whether the affected person will have to observe a very strict diet or only a relatively strict diet depends on the residual activity of the enzyme.
There are enzyme supplements available on the market for this dissacharidase deficiency. They can be used to alleviate a strict diet regime.
If you do have sucrose intolerance diagnosed by your doctor, please consult experts in nutrition to create a good and healthy diet for yourself!
1) Treem, William R.; Congenital Sucrase-Isomaltase Deficiency. Journal of Pediatric Gastroenterology & Nutrition: July 1995 - Volume 21 - Issue 1 - ppg 1-14