Lactose Intolerance – Symptoms, Test, Diet, Treatment

What is lactose intolerance?

Lactose intolerance is the inability to digest lactose (milk sugar) because of a lactase deficiency. Lactase is an enzyme that breaks down lactose to glucose and galactose, which are normally completely absorbed from the small intestine into the blood. In lactose deficiency, undigested lactose remains in the gut where it causes bloating and diarrhea, mainly after consuming dairy.

Lactose intolerance is not the same as a milk allergy, which occurs mainly in children where there may be allergic symptoms like tingling lips or mouth, itchy skin, and other symptoms of food allergy. Instead lactose intolerance is a disturbance with digesting the milk sugar known as lactose. The residual lactose then irritates the bowels thereby giving rise to the characteristic symptoms of lactose which arises after meals laden with dairy.

Types of Lactose Intolerance

Lactase is an enzyme produced and secreted  by the small intestine where it helps with the digestion of lactose (milk sugar). If this enzyme is lacking or deficient then lactose cannot be broken down. The remaining lactose in the gut can then have a number of different effects on the bowels which leads to the symptoms seen in lactose intolerance.

  • The amount of enzyme lactase in some individuals tends to lower through the years from an unknown reason; symptoms of lactose intolerance typically appear in adolescence or early adulthood, but often not until old age.  This is called primary lactose intolerance. Lactose intolerance in small children, especially under one year of age, is not common.
  • Inherited (recessive autosomal) lack of lactase is rare and in this case a baby has a diarrhea from birth.
  • In extensive intestinal inflammation (in infection, Crohn’s disease, celiac disease), production of lactase in the small intestine may be reduced so temporary lactose intolerance may occur. This is secondary lactose intolerance.
  • Surgical removal of part of the small intestine may cause permanent secondary lactose intolerance.
  • During and after a bout of diarrhea due to other causes, a person may become temporarily intolerant to dairy. This is anther form of secondary lactose intolerance.

Symptoms of Lactose Intolerance

In individuals with lactase deficiency, ingested lactose, undigested in small intestine, reaches the colon where it is broken down by normal colonic bacteria, which produce gas, thus causing bloating and flatulence. Lactose also draws water into the bowel (by osmotic effect) thus causing diarrhea.

Symptoms appear approximately 30 minutes to 2 hours after the meal. Some lactose intolerant people can digest small amount of dairy products while others cannot conumed even small amounts of dairy without experiencing symptoms. The amount of lactose that the affected person can digest decreases with age.

Read more on the signs of lactose intolerance.

Tests for Lactose Intolerance

a) Lactose-free diet trial. Complete cessation of symptoms after 2-3 days of lactose-free diet is highly indicative of lactose intolerance.

b) Hydrogen breath test with lactosedetects an amount of hydrogen in expired air few hours after a lactose-rich meal. In lactase deficiency, undigested lactose travels toward the colon where normal colonic bacteria break it down and produce hydrogen – this is then absorbed into the blood and appears in exhaled air.

c) In lactose intolerance test, blood glucose level is checked after a lactose-rich meal. Normally (in the presence of enzyme lactase), lactose is broken into glucose and galactose, which both are absorbed into the blood, and increased level of glucose in the blood can be detected. In lactase deficiency, lactose is not broken down and glucose level in the blood doesn’t rise. This test is rarely performed today, though.

d) In infants, a stool acidity test reveals acidic stool when lactose is present in it.

Prevention and Treatment of Lactose Intolerance

Lactose intolerance, as a disorder, currently can be neither prevented nor treated. However, the condition can be managed and the symptoms can be prevented by abstaining from dairy. There may individual tolerance to dairy – some people with a milder form of this intolerance can consume small amounts of dairy and remain symptom-free.

Lactose-Free Diet

With lactose-free diet, all symptoms of lactose intolerance usually disappear completely in 2-3 days, if there is no additional cause of chronic bloating and flatulence, or chronic diarrhea.

Main lactose-containing foods are: all sorts of milk (cow’s, goat’s, sheep milk, breast milk, except non-real milk like soy milk, and lactose-free milk from which lactose was removed), yogurts, soft cheese (they are only traces of lactose in most hard cheeses), butter, ice-cream and products where milk is an ingredient: puddings, chocolates, pastries, cookies, etc.

Small amounts of milk in one meal may be tolerated and milk ingested together with other foods may be digested easier. Lactose-free milk also exists. Soy formula may be appropriate for infants, since it contains a lot of calcium. Other calcium reach foods include broccoli, okra, kale, collards, turnip greens, canned fish, almonds, calcium fortified soy milk, tofu or soybeans.

People who are intolerant to even small amounts of milk, should be aware that lactose may be found in some breads, cereals, instant foods, pre-prepared food mixes, margarine, salad dressings, candies, coffee creamers (even if labeled as non-diary), beers, cream liquors and products labeled as: “Dry milk solids”, “Whey”, “Curds”, “Milk by-products”, “Non-fat dry milk powder”, etc. Lactose in traces may be found in some drugs, supplements, over the counter products or contraceptive pills.

Read more on foods to eat and avoid in lactose intolerance.

Lactase Pills

The enzyme lactase in capsules is available but this does not offer relief to every person with lactose intolerance. Capsules should be taken before the lactose-containing meal. Dairy can be digested this way but this is not the optimal solution.


Some probiotic yogurts or other probiotic products contain bacteria that synthesize lactase (should be denoted on the product label), which digests lactose in the product.


Some lactose intolerant individuals, especially children, may need calcium supplements since they may not get enough calcium from other foods.

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