Diagnosis of galactosemia is by measuring the activity of gal-l-P-transferuse in erythrocytes. Galactose should be restricted if the gal-1 -P-transferase is elevated above 2 mg/dl.

Objectives of diet therapy in galactosemia are to prevent symptoms and to provide nutrients for normal growth and development. Treatment should begin in the first few days of life itself. The goal of dietary treatment for galactosemia is to minimize galactose intake which in turn minimizes galactose-l-phosphate production. Therefore, dietary treatment of galactosemia is to remove any foods containing galactose from the diet. Because milk and milk products are the most common food source of galactose, persons with galactosemia should avoid these foods. The diet allows most protein-containing foods other than milk and milk products. Fruits, vegetables, grains, breads, fats and sugars are acceptable, as long as they do not have ingredients that contain galactose. Some fruits and vegetables do contain small amounts of galactose.

Patient or the family members of the patients must be educated to read food labels while purchasing food. The labels of all processed foods must be read carefully for ingredients it contains. The milk products to be avoided in processed foods are milk, casein, dry milk solids, lactose, curds and whey. The milk proteins casein and caseinate must be limited in the diet. They can provide large amounts of galactose if many foods or large amounts of any food containing casein are eaten. The following products may be used because they do not contain lactose: lactate, lactic acid, lactylates and calcium compounds.

Milk and milk products are the usual dietary source of calcium. Because persons with galactosemia remove milk products from their diet, they need to add calcium back into their diet through supplements. All people with galactosemia should be given a regular daily supplement of calcium. A soy-based formula can be used or tablets can be given. Fermented soy products (fermented soy sauce, miso etc.) are not recommended as galactose can be released in the fermentation process. Non-fermented soy products (tofu, textured vegetable protein, and soybean extract) are acceptable.