Lactose intolerance is a condition where an individual experiences stomach discomfort after consuming milk and dairy products which contain lactose. The discomfort originates in the intestines and is caused by the deficiency of an enzyme (lactase) that enables the intestinal tract to digest and breakdown lactose for the use of the body.
Lactose intolerance is related to regulation of the lactase levels in adulthood. The level of lactase expression is higher during childhood and enables babies to properly digest the maternal milk. In most mammal species, milk consumption is restricted to the lactation phase during infancy and the patterns of lactase expression are genetically regulated to follow this trend, with a decrease in levels of expression after infancy. However, with the introduction of animal milk and its derivatives in the diet of adult humans, lactose consumption is no more restricted to infancy in our species. In some individuals, the presence of lactose induces more expression of lactase, opposing the natural trend to reduce its levels and permitting proper digestion of milk. However, in others, these mechanisms are not as efficient, either because they fail to respond or because response is too slow.
It is estimated that 70% of all adults have lactose intolerance, and this condition is concentrated especially on societies where milk intake is weaned on early age and where the diet is not traditionally centered on milk and its products. This is especially true for Native Americans, African-Americans, Southeast Asians, Chinese, Australian Aborigines, Eskimos, Central Asians and Lebanese where the percentage of those with lactose intolerance is very high. However, in some societies where milk products are introduced early in development and are frequently consumed, the incidence of lactose intolerance drops. The relationship between prevalence of lactose intolerance and milk consumption patterns after infancy arises from the inducible nature of the lactase gene. If exposure to lactose is continued after lactation the individual is less likely to develop intolerance in adulthood.
Lactose intolerance should not be confused with milk allergy and irritable bowel syndrome. Milk allergy is a condition where the body's immune system reacts excessively to milk proteins and produces hives, urticaria, stomach upset, and difficulty of breathing. Irritable bowel syndrome is another condition in which there is a chronic malfunction in digestive motility and results in either diarrhea or constipation in response to stress and certain foods.
The cause of lactose intolerance are low-levels of lactase production which is a critical enzyme to break down lactose into more simple sugars. Lactase enables babies to depend on milk for food and nutrition. However, in later years, the lactase production decreases along with the ability to break down lactose. If too much milk is taken, unused lactose stays in the intestines where it is broken down by native bacteria in the intestines. The bacteria breaks down lactose via fermentation and releases gases like hydrogen, methane, nitrogen and carbon dioxide. These gases accumulate in the intestines and cause discomfort in the stomach, excessive belching and flatulence. The lactose particles also collect water from the intestines leading to sudden diarrhea.
Lactose intolerance symptoms are usually present in other digestive disorders.
- Abdominal pain
- Abdominal distension
- Diffuse and sudden diarrhea
- Sensation of increased motility, termed commonly as “rumbling stomach”
For the diagnosis of lactose intolerance, the digestive system is challenged by ingesting small amounts of lactose-containing products. It may trigger a body response that varies among individuals and patients who are advised to report immediately any severe symptoms. The diagnosis of lactose intolerance should be clearly discerned from milk allergy. To distinguish these conditions, lactose-free milk is also administered; a person with milk allergy will react to both lactose-free and normal milk. However there is the possibility that a patient may suffer from both conditions.
There are three tests that enable accurate diagnosis of lactose intolerance:
Hydrogen breath test is the most commonly performed examination to identify lactose intolerance. The test is done after an overnight fast, after which 50 grams of lactose is administered to the patient. In lactose intolerant individuals, bacteria will break down unused lactose and produce large amounts of hydrogen with methane which are readily detected. The test takes two to three hours.
Stool acidity test is also performed after a lactose challenge to check for the presence of lactose breakdown products in the stool, which are acidic.
Intestinal biopsy is an invasive procedure in which a sample of the intestinal tissue is removed and analyzed for lactase enzymes and RNA from tissue. This is an experimental test and is not regularly applied in the clinical setting.
Treatment approaches currently available include administration of probiobiotics, lactase- or hydrolyzed lactose-containing supplements and lowering the consumption of milk and its products. If it is not possible to reduce milk intake, it might be necessary to find alternatives like soy, rice, almond, coconut and peanut milk. Is important to read food labels and choose products with the lowest lactose content.
Normally, lactose intolerance does not significantly impact daily activities as long as the recommended treatment and lifestyle changes are followed. Lactose intolerant individuals may still be able to consume milk products in small amounts.
Limiting milk products is usually enough to prevent symptoms of lactose intolerance.
People with lactose intolerance should avoid or reduce consumption of milk and products made from milk, such as ice cream, cheese and yogurt. Patients are advised to use alternative sources of calcium, such as nutritional supplements.
Research focuses on establishing efficient methods to manage lactose intolerance and to clarify the underlying mechanisms that lead to the development of this condition.