The symptoms depend on the quantity of lactose ingested and the ability of the body to digest the amount of lactose. This in turn depends on the extent of lactase deficiency.

The main symptoms presented by the patients are abdominal fullness or bloating, nausea, abdominal pain, diarrhea and flatulence [11]. Borborygmi may also be experienced.

On physical examination, the abdomen may be tender. One may feel the bloating of the abdomen. Auscultation may reveal borborygmi sounds.

Diagnosis of lactose intolerance can be done with a complete history and by certain dietary manipulations. There are few laboratory tests which aid in the diagnosis.

One of them is lactose tolerance test. In this test, the fasting blood glucose levels are measured. Then 50g lactose is given [12]. Serial blood glucose levels are measured as 0, 60, 120 minutes. If the levels increase less than 20 mg/dL above the fasting level then the test is positive. False negative results occur in cases with diabetes, abnormal gastrointestinal emptying etc [13].

The other is milk tolerance test. 500 ml of milk is given and if the glucose levels rise less than 9 mg/dL, then it indicates lactose intolerance [14].

Breath hydrogen test is more specific as compared to lactose tolerance test [6]. Patients are given lactose and then the expired air is assessed for hydrogen gas concentrations. Rise in the concentration more than 20 ppm after lactose administration indicates lactose intolerance due to lactase deficiency [12]. Sleep, exercise, smoking, aspirin use can cause false-positive results.

Dietary manipulations involve diagnosing lactose intolerance by reducing intake of lactose-containing foods to check disappearance of the symptoms. The symptoms reappear as soon as lactose-containing foods are re-started [15] [16].

Small bowel biopsy is very rarely performed though it is a confirmatory test. Biopsy samples of the small intestine are tested for lactase activity.

One can use various imaging techniques in cases where secondary causes of lactose intolerance are to be detected.

Most individuals can manage the symptoms by simple dietary modifications. Some can tolerate cheese better than milk, so instead of milk one can consume milk products like cheese or yogurt for daily calcium intake. Some who can tolerate small amounts of lactose may need to limit lactose intake or change the form in which they consume it. For example, some individuals can tolerate milk when combined with other meals like cereals, or cheese spread over other foods. Some individuals may need to stop lactose completely.

One must also make note and avoid all other non-dairy products and grocery items which contain lactose like bread, margarine, salad dressing, some snacks or candies, certain medications etc.

A dietary plan will help control the symptoms and not compensate on the nutrients. In cases of secondary lactose intolerance, one must treat the underlying cause to control lactose intolerance.

Lactose-free or lactose-reduced milk or milk products which are treated with lactase enzyme are recommended to meet the nutritional needs. Lactase tablets which help digest lactose from the food can be consumed along with lactose-containing foods.

Non-milk products like fish, dark green leafy vegetables are high in calcium content. Foods fortified with calcium and vitamin D can meet the nutritional needs of the body.

Lactose intolerance has a very good prognosis with appropriate dietary care. Osteopenia can be observed as a complication to lactose intolerance [9] [10].

Lactose intolerance is said to occur when an individual suffers from lactase enzyme deficiency and the resulting malabsorption. Lactose is not well digested and undigested lactose may pass through the intestines producing gastrointestinal symptoms.

Lactase deficiency can cause three types of lactose intolerances as follows:

1. Primary lactose intolerance: This is one of the commonest causes of lactose intolerance where the production of lactase reduces after about 2 years of age or even later. They could digest lactose initially but cannot do so now due to lactase deficiency.
2. Secondary lactose intolerance: This occurs when the mucosa of the small intestine is damaged due to any infection or acute illness. It can be caused due to diseases like acute gastroenteritis, giardiasis, ascariasis, gastrinoma, chemotherapy etc. This can happen at any point in life.
3. Congenital lactose intolerance: Is an autosomal-recessive trait and hence is very rare [2] [3]. There is deficient lactase enzyme production right from birth.

The incidence of lactose intolerance differs depending on the race. The incidence among southern Europeans is about 25 to 30% while that among the Native Americans and Asian Americans is about 75 to 90% [4]. The prevalence of lactose intolerance is highest among Asians, South Americans and Africans.

Commonly affected age group is from 20 to 40 years old [2] [5]. Its prevalence among both the genders is equal. During pregnancy, some of the women tend to recover their ability to digest lactose.

Lactose is digested and broken down into glucose and galactose by the enzyme lactase produced by the intestinal villi. In cases where lactase is deficient, this process of hydrolysis is averted. The unabsorbed lactase triggers increased secretion of fluid and electrolytes in the intestine till the osmotic balance is reached.

The intestine itself cannot maintain a high electrochemical gradient between the contents and the blood; hence there is fluid influx which is about three times the osmolality of lactose [6] [7].

This osmosis increases the rate of the intestinal movement causing indigestion. The free lactose is fermented in the bowel by the colonic bacteria into short-chain fatty acids and releases hydrogen gas [8]. The increased bowel movements, the excess fluid and gases lead to the gastrointestinal symptoms like bloating, flatulence, diarrhea, abdominal discomfort, etc.

One cannot prevent lactose intolerance but one can definitely control the discomfort and reduce the intensity of the symptoms one experiences due to intake of lactose.

Individuals must read labels carefully on all products. One must not only look out for words like milk or lactose but also for whey, curds, milk products, milk powder etc.

Avoiding intake of milk in the direct form can help reduce symptoms. Instead try consuming milk products or blend it with other food products.

Lactose is a disaccharide, a sugar found in milk as well as milk products. The name comes from ‘lac’ or ‘lactis’, the latin word for milk. The intestinal villi produce an enzyme called lactase (β-D-galactosidase). This enzyme breaks down lactose into simple, monosaccharide sugars - glucose and galactose. These are then absorbed easily into the blood.

Lactose intolerance implies an inability to digest lactose and break it into glucose and galactose due to deficiency or lack of lactase called as hypolactasia [1].

Lactose is a type of sugar found in milk and milk products. Deficiency of an enzyme lactase leads to lactose intolerance. Lactase breaks down lactose into simpler sugars called glucose and galactose. When lactose doesn’t get digested it leads to symptoms like abdominal bloating, diarrhoea, pain and flatulence.

Diagnosis is made by taking a detailed history and dietary manipulations. Medical tests like lactose tolerance test, breath hydrogen test, biopsy etc. help to diagnose it. One must rule out other causes of digestive disturbances like milk allergy, inflammatory bowel disease etc. as the symptoms can be misleading.

Individuals with lactose intolerance have a variable amount of lactose they can safely tolerate. Many individuals can manage the symptoms by dietary modifications. Some may need to restrict lactose-containing foods like milk and milk products while others may have to stop it completely. One must read the labels of all products to check any sources of lactose in it. A dietary plan can help one to meet the nutritional needs of the body. One can consume calcium and vitamin D supplements or fortified foods to compensate for the lack of milk in the diet.