Xylose isomerase acts to convert fructose sugars into glucose. Dietary supplements of xylose isomerase may improve the symptoms of fructose malabsorption.

Fructose and fructans are FODMAPs (fermentable oligo-, di- and mono-saccharides and polyols) known to cause gastrointestinal discomfort in susceptible individuals. A low FODMAP diet has widespread application for managing functional gastrointestinal disorders such as IBS.

Treatment of HFI depends on the stage of the disease, and the severity of the symptoms. Stable patients without acute intoxication events are treated by careful dietary planning that avoids fructose and its metabolic precursors. Fructose is replaced in the diet by glucose, maltose or other sugars. Management of patients with HFI often involves dietitians who have a thorough knowledge of what foods are acceptable.

To treat people with a deficiency of this enzyme, they must avoid needing gluconeogenesis to make glucose. This can be accomplished by not fasting for long periods, and eating high-carbohydrate food. They should avoid fructose containing foods (as well as sucrose which breaks down to fructose).

As with all single-gene metabolic disorders, there is always hope for genetic therapy, inserting a healthy copy of the gene into existing liver cells.

Sucrose intolerance can be caused by genetic mutations in which both parents must contain this gene for the child to carry the disease (so-called primary sucrose intolerance). Sucrose intolerance can also be caused by irritable bowel syndrome, aging, or small intestine disease (secondary sucrose intolerance). There are specific tests used to help determine if a person has sucrose intolerance. The most accurate test is the enzyme activity determination, which is done by biopsying the small intestine. This test is a diagnostic for GSID. Other tests which can aid in the diagnosis of GSID but which are not truly diagnostic for the disease are the sucrose breath test, and a genetic test which tests for the absence of certain genes which are thought to be responsible for GSID.

Sucrose (also termed "saccharose") is a disaccharide and is a two-sugar chain composed of glucose and fructose which are bonded together. A more familiar name is table, beet, or cane sugar. It was believed that most cases of sucrose intolerance were to do an autosomal recessive, genetic, metabolic disease. Based on new data patients with heterozygous and compound heterozygous genotypes can have symptom presentation as well. GSID involves deficiency in the enzyme sucrase-isomaltase, which breaks apart the glucose and fructose molecules. When disaccharides are consumed, they must be broken down into monosaccharides by enzymes in the intestines before they can be absorbed. Monosaccharides, or single sugar units, are absorbed directly into the blood.

A deficiency of sucrase may result in malabsorption of sugar, which can lead to potentially serious symptoms. Since sucrose-isomaltase is involved in the digestion of starches, some GSID patients may not be able to absorb starches as well. It is important for those with sucrose intolerance to minimize sucrose consumption as much as possible. Dietary supplements or medications may be taken as a substitute for the enzyme missing or to introduce healthy bacteria into the immune system.

Glucose-galactose malabsorption is a rare condition in which the cells lining the intestine cannot take in the sugars glucose and galactose, which prevents proper digestion of these molecules and larger molecules made from them.

Glucose and galactose are called simple sugars, or monosaccharides. Sucrose and lactose are called disaccharides because they are made from two simple sugars, and are broken down into these simple sugars during digestion. Sucrose is broken down into glucose and another simple sugar called fructose, and lactose is broken down into glucose and galactose. As a result, lactose, sucrose and other compounds made from carbohydrates cannot be digested by individuals with glucose-galactose malabsorption.

Because of the ease of therapy (dietary exclusion of fructose), HFI can be effectively managed if properly diagnosed. In HFI, the diagnosis of homozygotes is difficult, requiring a genomic DNA screening with allele specific probes or an enzyme assay from a liver biopsy. Once identified, parents of infants who carry mutant aldolase B alleles leading to HFI, or older individuals who have clinical histories compatible with HFI can be identified and counselled with regard to preventive therapy: dietary exclusion of foods containing fructose, sucrose, or sorbitol. If possible, individuals who suspect they might have HFI, should avoid testing via fructose challenge as the results are non-conclusive for individuals with HFI and even if the diagnostic administration fructose is properly controlled, profound hypoglycemia and its sequelae can threaten the patient's well-being.

The primary treatment method for fatty-acid metabolism disorders is dietary modification. It is essential that the blood-glucose levels remain at adequate levels to prevent the body from moving fat to the liver for energy. This involves snacking on low-fat, high-carbohydrate nutrients every 2–6 hours. However, some adults and children can sleep for 8–10 hours through the night without snacking.

Treatment is directed largely towards management of underlying cause:

- Replacement of nutrients, electrolytes and fluid may be necessary. In severe deficiency, hospital admission may be required for nutritional support and detailed advice from dietitians. Use of enteral nutrition by naso-gastric or other feeding tubes may be able to provide sufficient nutritional supplementation. Tube placement may also be done by percutaneous endoscopic gastrostomy, or surgical jejunostomy. In patients whose intestinal absorptive surface is severely limited from disease or surgery, long term total parenteral nutrition may be needed.

- Pancreatic enzymes are supplemented orally in pancreatic insufficiency.

- Dietary modification is important in some conditions:

- Gluten-free diet in coeliac disease.

- Lactose avoidance in lactose intolerance.

- Antibiotic therapy to treat Small Bowel Bacterial overgrowth.

- Cholestyramine or other bile acid sequestrants will help reducing diarrhoea in bile acid malabsorption.

Ketosis is deliberately induced by use of a ketogenic diet as a medical intervention in cases of intractable epilepsy. Other uses of low-carbohydrate diets remain controversial. Carbohydrate deprivation to the point of ketosis has been argued to have both negative and positive effects on health.

Carnitor - an L-carnitine supplement that has shown to improve the body's metabolism in individuals with low L-carnitine levels. It is only useful for Specific fatty-acid metabolism disease.

Sucrose intolerance, also called sucrase-isomaltase deficiency, congenital sucrase-isomaltase deficiency (CSID), or genetic sucrase-isomaltase deficiency (GSID), is the condition in which sucrase-isomaltase, an enzyme needed for proper metabolism of sucrose (sugar) and starch (i.e., grains and rice), is not produced or the enzyme produced is either partially functional or non-functional in the small intestine. All GSID patients lack fully functional sucrase, while the isomaltase activity can vary from minimal functionality to almost normal activity. The presence of residual isomaltase activity may explain why some GSID patients are better able to tolerate starch in their diet than others with GSID.

The highest prevalence rates are seen in the Inuit populations of Greenland (5–10%), Alaska (3–7%) and Canada (about 3%). European descent prevalence ranges from 0.2% to 0.05%. There is a lower prevalence reported in African Americans and Hispanics compared to Caucasians.

Some clinicians regard eliminating carbohydrates as unhealthy and dangerous. However, it is not necessary to eliminate carbohydrates from the diet completely to achieve ketosis. Other clinicians regard ketosis as a safe biochemical process that occurs during the fat-burning state. Ketosis, which is accompanied by gluconeogenesis (the creation of glucose de novo from pyruvate), is the specific state that concerns some clinicians. However, it is unlikely for a normally functioning person to reach life-threatening levels of ketosis, defined as serum beta-hydroxybutyrate (B-OHB) levels above 15 millimolar (mM) compared to ketogenic diets among non diabetics, which "rarely run serum B-OHB levels above 3 mM." This is avoided with proper basal secretion of pancreatic insulin. People who are unable to secrete basal insulin, such as type 1 diabetics and long-term type II diabetics, are liable to enter an unsafe level of ketosis, eventually resulting in a coma that requires emergency medical treatment. The anti-ketosis conclusions have been challenged by a number of doctors and advocates of low-carbohydrate diets, who dispute assertions that the body has a preference for glucose and that there are dangers associated with ketosis.

Glucose-galactose malabsorption generally becomes apparent in the first few weeks of a baby's life. Affected infants experience severe diarrhea resulting in life-threatening dehydration, increased acidity of the blood and tissues (acidosis), and weight loss when fed breast milk or regular infant formulas. However, they are able to digest fructose-based formulas that do not contain glucose or galactose. Some affected children are better able to tolerate glucose and galactose as they get older.

Small amounts of glucose in the urine (mild glucosuria) may occur intermittently in this disorder. Affected individuals may also develop kidney stones or more widespread deposits of calcium within the kidneys.

Glucose-galactose malabsorption is a rare disorder; only a few hundred cases have been identified worldwide. However, as many as 10 percent of the population may have a somewhat reduced capacity for glucose absorption without associated health problems. This condition may be a milder variation of glucose-galactose malabsorption.

There is no cure for GALT deficiency, in the most severely affected patients, treatment involves a galactose free diet for life. Early identification and implementation of a modified diet greatly improves the outcome for patients. The extent of residual GALT enzyme activity determines the degree of dietary restriction. Patients with higher levels of residual enzyme activity can typically tolerate higher levels of galactose in their diets. As patients get older, dietary restriction is often relaxed. With the increased identification of patients and their improving outcomes, the management of patients with galactosemia in adulthood is still being understood.

After diagnosis, patients are often supplemented with calcium and vitamin D3. Long-term manifestations of the disease including ovarian failure in females, ataxia. and growth delays are not fully understood. Routine monitoring of patients with GALT deficiency includes determining metabolite levels (galactose 1-phosphate in red blood cells and galactitol in urine) to measure the effectiveness of and adherence to dietary therapy, ophthalmologic examination for the detection of cataracts and assessment of speech, with the possibility of speech therapy if developmental verbal dyspraxia is evident.

It is important for MADD patients to maintain strength and fitness without exercising or working to exhaustion. Learning this balance may be more difficult than normally, as muscle pain and fatigue may be perceived differently from normal individuals.

Symptomatic relief from the effects of MADD may sometimes be achieved by administering ribose orally at a dose of approximately 10 grams per 100 pounds (0.2 g/kg) of body weight per day, and exercise modulation as appropriate. Taken hourly, ribose provides a direct but limited source of energy for the cells. Patients with myoadenylate deaminase deficiency do not retain ribose during heavy exercise, so supplementation may be required to rebuild levels of ATP.

Creatine monohydrate could also be helpful for AMPD patients, as it provides an alternative source of energy for anaerobic muscle tissue and was found to be helpful in the treatment of other, unrelated muscular myopathies.

The only treatment for classic galactosemia is eliminating lactose and galactose from the diet. Even with an early diagnosis and a restricted diet, however, some individuals with galactosemia experience long-term complications such as speech difficulties, learning disabilities, neurological impairment (e.g. tremors, etc.), and ovarian failure. Symptoms have not been associated with Duarte galactosemia, and many individuals with Duarte galactosemia do not need to restrict their diet at all. However, research corroborates a previously overlooked theory that Duarte galactosemia may lead to language developmental issues in children with no clinical symptoms. Infants with classic galactosemia cannot be breast-fed due to lactose in human breast milk and are usually fed a soy-based formula.

Galactosemia is sometimes confused with lactose intolerance, but galactosemia is a more serious condition. Lactose intolerant individuals have an acquired or inherited shortage of the enzyme lactase, and experience abdominal pains after ingesting dairy products, but no long-term effects. In contrast, a galactosemic individual who consumes galactose can cause permanent damage to their bodies.

Long term complication of galactosemia includes:

- Speech deficits

- Ataxia

- Dysmetria

- Diminished bone density

- Premature ovarian failure

- Cataract

The goal for treatment of GSD type 0 is to avoid hypoglycemia. This is accomplished by avoiding fasting by eating every 3-4 hours during the day. At night, uncooked corn starch can be given because it is a complex glucose polymer. This will be acted on slowly by pancreatic amylase and glucose will be absorbed over a 6 hour period.

Inborn errors of carbohydrate metabolism are inborn error of metabolism that affect the catabolism and anabolism of carbohydrates.

An example is lactose intolerance.

Carbohydrates account for a major portion of the human diet. These carbohydrates are composed of three principal monosaccharides: glucose, fructose and galactose; in addition glycogen is the storage form of carbohydrates in humans. The failure to effectively use these molecules accounts for the majority of the inborn errors of human carbohydrates metabolism.

There is no broadly accepted standard of care for infants with DG. Some healthcare providers recommend partial to complete dietary restriction of milk and other high galactose foods for infants or young children with DG; others do not. Because children with DG develop increased tolerance for dietary galactose as they grow, few healthcare providers recommend dietary restriction of lactose or galactose beyond early childhood.

The rationale for NOT restricting dietary galactose exposure of infants and/or young children with DG: Healthcare providers who do not recommend dietary restriction of galactose for infants with DG generally consider DG to be of no clinical significance—meaning most infants and children with DG seem to be doing clinically well. Further, these providers may be opposed to interrupting or reducing breastfeeding when there is no clear evidence it is contraindicated. These providers may argue that the recognized health benefits of breastfeeding outweigh the potential risks of as yet unknown negative effects of continued milk exposure for these infants. For infants with DG who continue to drink milk, some doctors would recommend that blood galactose-1-phosphate (Gal-1P) or urinary galactitol be rechecked by age 12 months to ensure that these metabolite levels are normalizing.

The rationale FOR restricting dietary galactose exposure of infants and/or young children with DG: Healthcare providers who recommend partial or complete dietary restriction of galactose for infants and/or young children with DG generally cite concern about the unknown long-term consequences of abnormally elevated galactose metabolites in a young child's blood and tissues. Infants with DG who continue to drink milk accumulate the same set of abnormal galactose metabolites seen in babies with classic galactosemia – e.g. galactose, Gal-1P, galactonate, and galactitol – but to a lesser extent. While it remains unclear whether any of these metabolites contribute to the long-term developmental complications experienced by so many older children with classic galactosemia, the possibility that they might cause problems serves to motivate some healthcare providers to recommend dietary galactose restriction for infants with DG. Switching an infant with DG from milk or milk formula (high galactose) to soy formula (low galactose) rapidly normalizes their galactose metabolites. This approach is considered potentially preventative rather than responsive to acute symptoms.

If dietary galactose restriction of any kind is followed, healthcare providers may recommend that the child have a galactose challenge to re-evaluate galactose tolerance before the restrictive diet is discontinued. Most infants or young children with DG who are followed by a metabolic specialist are discharged from follow up after a successful galactose challenge.Options for those choosing to restrict dietary galactose in infancy and/or early childhood: Dietary restriction practices for Duarte galactosemia vary widely. In the US, some healthcare providers recommend full dietary restriction of milk and all dairy products for the first 12 months of life, followed by a galactose challenge. Some providers recommend the galactose challenge before 12 months, others after. Some providers who recommend dietary intervention suggest a "compromise approach" if the parent wishes to breastfeed, such that the parent alternates feedings of breast milk and low galactose formula. Finally, some parents choose to continue some form of dietary galactose restriction for their child with DG beyond early childhood.

What is a galactose challenge? The goal of a galactose challenge is to learn whether a child is able to metabolize dietary galactose sufficiently to prevent the abnormal accumulation of galactose metabolites, generally measured as Gal-1P in the blood. For infants with DG who showed elevated galactose metabolites at diagnosis, this test can be used to see if their ability to process galactose has improved enough to discontinue dietary galactose restriction.

To test galactose metabolism, a baseline Gal-1P level is measured while the child is on a galactose-restricted diet. If the level is within the normal range (e.g. <1.0 mg/dL), the parent/guardian is advised to "challenge" the child with dietary galactose—meaning feed the child a diet that includes normal levels of milk for 2–4 weeks. Immediately after that time, another blood sample is collected and analyzed for Gal-1P level. If this second result is still in the normal range, the child is said to have "passed" their galactose challenge, and dietary galactose restrictions are typically relaxed or discontinued. If the second test shows elevated Gal-1P levels, the parent/guardian may be advised to resume galactose restriction for the child, and the "challenge" may be repeated after a few months.

Management for mitochondrial trifunctional protein deficiency entails the following:

- Avoiding factors that might precipitate condition

- Glucose

- Low fat/high carbohydrate nutrition

Glycogen-storage disease type 0 is most commonly diagnosed during infancy and early childhood.

The primary treatment goal is prevention of hypoglycemia and the secondary metabolic derangements by frequent feedings of foods high in glucose or starch (which is readily digested to glucose). To compensate for the inability of the liver to provide sugar, the total amount of dietary carbohydrate should approximate the 24-hour glucose production rate. The diet should contain approximately 65–70% carbohydrate, 10–15% protein, and 20–25% fat. At least a third of the carbohydrates should be supplied through the night, so that a young child goes no more than 3–4 hours without carbohydrate intake

In the last 30 years, two methods have been used to achieve this goal in young children: (1) continuous nocturnal gastric infusion of glucose or starch; and (2) night-time feedings of uncooked cornstarch. An elemental formula, glucose polymer, and/or cornstarch can be infused continuously through the night at a rate supplying 0.5–0.6 g/kg/h of glucose for an infant, or 0.3–0.4 for an older child. This method requires a nasogastric or gastrostomy tube and pump. Sudden death from hypoglycemia has occurred due to malfunction or disconnection, and periodic cornstarch feedings are now preferred to continuous infusion.

Cornstarch is an inexpensive way to provide gradually digested glucose. One tablespoon contains nearly 9 g carbohydrate (36 calories). Although it is safer, less expensive, and requires no equipment, this method does require that parents arise every 3–4 hours to administer the cornstarch. A typical requirement for a young child is 1.6 g/kg every 4 hours.

Long-term management should eliminate hypoglycemic symptoms and maintain normal growth. Treatment should achieve normal glucose, lactic acid, and electrolyte levels, and only mild elevations of uric acid and triglycerides.

Galactose is converted into glucose by the action of three enzymes, known as the Leloir pathway. There are diseases associated with deficiencies of each of these three enzymes:

In fructose bisphosphatase deficiency, there is not enough fructose bisphosphatase for gluconeogenesis to occur correctly. Glycolysis (the breakdown of glucose) will still work, as it does not use this enzyme.