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Metabolic Disorders
Calcium Imbalance
Chloride Imbalance
Gaucher's Disease
Glycogen Storage Diseases
Lactose Intolerance
Magnesium Imbalance
Metabolic Acidosis
Metabolic Alkalosis
Phosphorus Imbalance
Potassium Imbalance
Sodium Imbalance
Syndrome of Inappropriate Antidiuretic Hormone Secretion
Tay-Sachs Disease

Lactose Intolerance

What is Lactose Intolerance ?

Lactose intolerance is the inability to digest and absorb lactose, the main carbohydrate in milk. It stems from an insufficiency of the enzyme lactase.

Lactose intolerance may be congenital (rare) or acquired. In primary acquired lactose intolerance, the most common form, lactase levels start to decline between ages 2 and 3. By the time the patient reaches adolescence or early adulthood, lactase levels are decreased by about 90% of neonatal levels. This deficiency continues for life.

CULTURAL TIP: The incidence of lactose intolerance is high among certain ethnic groups, including Blacks, Orientals, Native Americans, Greek Cypriots, and some Ashkenazic Jews.

Causes of Lactose Intolerance

Both congenital and primary acquired lactose intolerance are thought to have a genetic basis.

Secondary acquired lactose intolerance may result from medical conditions, such as viral gastroenteritis, inflammatory bowel disease, celiac and sprue syndromes, and intestinal parasites, which disrupt the intestinal mucosa.

Lactose intolerance can also stem from medications that cause Gl disturbances (broad-spectrum antibiotics, colchicine, and certain chemotherapeutic drugs, such as antimetabolites). Ionizing radiation to the abdomen and surgery, such as small-bowel resection (with removal of some lactase-producing mucosa) or gastrectomy (with dumping syndrome), can also cause lactose intolerance. The effects may be temporary or permanent.

Signs & Symptoms of Lactose Intolerance

The signs and symptoms of lactose intolerance usually begin 30 minutes to two hours after eating or drinking foods that contain lactose. Common signs and symptoms include:

  • Abdominal fullness, gaseous
  • Malnutrition
  • Abdominal distention
  • Weight loss
  • Foul-smelling stools
  • Diarrhea
  • Very bad breath
  • Abdominal cramps
  • Gas

Diagnostic Tests

Lactose challenge testing is performed when lactose intolerance is suspected. In this test, the patient drinks a quart of skim milk on an empty stomach and notes any symptoms that develop within 4 hours. If the patient is lactase deficient, such symptoms as diarrhea and bloating occur within minutes to hours.

Lactose-free diet testing involves eliminating lactose from the patient's diet for a period of time, such as 5 days. If he becomes asymptomatic, the diagnosis is upheld.

Lactose tolerance testing is performed if the patient has a complicating disorder, such as celiac disease or gastroenteritis. In this test, a blood sample is taken after the patient has fasted overnight. Then the patient ingests a specified oral lactose load. Serum glucose levels are taken on blood samples drawn at specified intervals following lactose ingestion and on the fasting blood sample. A minimal increase (less than 20 mg/dl) in the serum glucose level and GI symptoms (cramping, flatulence, and perhaps diarrhea, confirm lactase deficiency.

Breath hydrogen analysis, a more sensitive and specific noninvasive test, is used to measure excess hydrogen exhalation, resulting from bacterial fermentation of lactose in the colon. (Hydrogen from the colon passes to the blood and then to the lungs.) Increased hydrogen content of expired air confirms lactose intolerance.

Small-bowel biopsy, rarely used, is used to determine whether lactose intolerance is primary or secondary. Only the secondary form shows abnormal epithelium.


For an infant with temporary lactose intolerance, a lactose-free formula may be substituted for breast milk or milk-based formula. Older children and adults wier temporary lactose intolerance must eliminate all milk products from the diet until the causative disorder improves.

Patients with genetic lactase deficiency must limit dietary lactose to the level they can comfortably tolerate. Some patients benefit from commercially available lactase enzyme products (LactAid, Lactrase), which may be added to milk or purchased ready to use. The commercial lactase reduces the lactose to glucose and galactose. Lactase enzyme capsules are also available.

Lactose-intolerant patients receiving tube feedings require a lactose-free formula (Resource or Ensure).

Prevention Tips

There is no known way to prevent the development of lactose intolerance.

Avoiding or restricting the amount of milk products in your diet can reduce or prevent symptoms.

Lactose intolerance is a natural occurrence that cannot be avoided. However, people can prevent symptoms by managing the condition with diet and lactase supplements.

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