Lactose Intolerance

Lactose Intolerance

Lactose intolerance is a common disorder caused by the inability to digest lactose, a carbohydrate found in milk and milk products. It typically causes symptoms of bloating, flatulence, diarrhea, and abdominal pain. Avoidance of milk and other dairy products alleviates most symptoms of lactose intolerance.


Lactose molecules cannot be directly absorbed by the body. Therefore, lactose has to be split into smaller molecules in order to be absorbed and transported across the wall of the intestines. Normally, lactose is broken up by an enzyme (protein that expedites chemical reactions in the body) called lactase.


This enzyme is located on the lining of the intestines (the brush border) and helps to break up lactose into its smaller carbohydrate components, glucose and galactose. These two smaller molecules are more easily absorbed by the body and used formetabolism.


Lactose intolerance is caused by a deficiency of lactase in the intestinal wall. As a result, the entire lactose molecule travels undigested in the small and large intestines. The lactose molecules draw water into the intestines (by a process similar to osmosis). This results in faster transit through the intestines, thus making the process of digestion even more difficult.


Eventually, bacteria present in the large intestine (colon) begin to digest (ferment) the lactose molecule by utilizing their own lactase enzyme, producing hydrogen gas and smaller molecules as byproducts. The combination of these processes leads to the symptoms of lactose intolerance: bloating, flatulence, diarrhea and abdominal pain.


Lactase enzymes levels are highest after birth and gradually decline thereafter. In African Americans, Asian Americans, and Native Americans the overall incidenceof lactose intolerance may be greater than 75% of the adult population. In Northern Europeans and Caucasians, the incidence rate is much less, typically under 25% of the adult population. In Hispanics, 50% of the adult population may have lactose intolerance, whereas, the highest rates are seen in some Asian populations, withprevalence rate greater than 90%.


It is important to recognize that deficiency in the lactase enzyme does not necessarily translate into lactose intolerance. Many people with mild degrees of lactase deficiency have no symptoms and are able tolerate lactose ingestion. On the other hand, people with severe lactase deficiency may have symptoms even with minimal amount of lactose ingestion.


The amount of lactose in the diet and the difference in the make up of bacteria in the colon are other factors that determine the variability and severity of symptoms in some individuals.


Symptoms of lactose intolerance include:

  • bloating.
  • abdominal pain.
  • diarrhea.
  • flatulence (passing gas).
  • nausea.


The production of gas (flatus) is the result of the activity of bacteria in the large intestine (colon). As the large lactose molecule passes unchanged through the small intestines, it is metabolized by the bacteria that are normally present in the colon. As a result, certain gases, such as hydrogen, are produced and are released from the rectum.


Additionally, a portion of the lactose reaching the colon does not get metabolized by the bacteria. Because these larger molecules are accompanied with an increase in secretion of water through osmosis, this results in the passage of loose stools and diarrhea.


Lactose intolerance is due to a basic deficiency of the lactase enzyme. This enzyme is normally found on the inner lining of the intestinal wall and splits the carbohydrate lactose into smaller components, glucose and galactose. These breakdown products are then absorbed and transported from the intestinal wall for further digestion.


Lactose intolerance may occur because of a deficient or completely absent lactase enzyme level. The complete absence of lactase is a rare genetic condition where the gene responsible for producing the lactase enzyme is defective. This form of lactase deficiency results in a marked lactose intolerance from birth.


More commonly, lactose intolerance is an acquired condition, not present at birth. The intestinal wall may become damaged due to a variety of reasons, commonly from infections or certain medications.


Some of the possible causes of lactase deficiency include:


The most common cause of lactose intolerance is the gradual loss of lactase after childhood. In this type of lactose intolerance, there is a genetically progressivedecrease in the lactase enzyme levels. In populations with high prevalence rates of lactose intolerance, a gradual loss of lactase is more common and begins at an earlier age. In Asians and Asian Americans, the decline in lactase enzyme levels is more prevalent, followed by Native Americans, African Americans, and Hispanics.


Self-Care at Home


Dietary changes designed to reduce or eliminate lactose products is the simplest and most effective treatment for lactose intolerance. Foods that should be avoided by people with lactose intolerance are listed in the previous section and include milk, ice cream, yogurt, and cheese.


Replacement of milk with substitutes, such as, soy milk and other soy products or rice milk is one option for people with lactose intolerance.


Lactase enzyme replacement in milk products is also a common recommendation for treating lactose intolerance. Lactase supplements in pill or liquid (Lactaid) form are available and can be added to milk. Other similar preparations include Lactrase, LactAce, Dairy Ease®, and Lactrol. Commercially available milk predigested with lactase is also available in most supermarkets (Lactaid milk).




As mentioned previously, the most important part of treating lactose intolerance are dietary changes to limit the intake of foods containing lactose. Usually, complete elimination of lactose from the diet is not necessary, as most people with this condition can tolerate some amount of lactose in their diet depending on the degree of lactase deficiency.


The highest concentration of lactose per serving is found in milk and ice cream. Cheese generally contains less lactose per serving than milk and ice cream. It is also important to note that lactose may be found in many food products other than milk and dairy.


Some of the common foods that may contain lactose are:

  • margarine,
  • some salad dressings,
  • bread and other baked goods,
  • breakfast cereals,
  • pancake, cookie, and biscuit mixes,
  • candy,
  • powdered coffee creamers,
  • dry milk, milk powder, nonfat milk powder,
  • curds.


It is prudent to read the list of ingredients on food labels to find out if lactose is present in food products.


Occasionally, lactose may be found in certain medications. Intake of these medications may cause side effects similar to the symptoms of lactose intolerance. For example, some birth control pills may contain lactose as an ingredient.


Among milk products, yogurt may be better tolerated by people with lactose intolerance; this is because bacteria that are used in preparing yogurt contain lactase and are able to split lactose into glucose and galactose before yogurt is ingested.




Because milk and milk containing products are the main sources of dietary calcium and vitamin D, people with lactose intolerance may be deficient in calcium and vitamin D. Calcium and vitamin D deficiency can lead to earlyosteoporosis and fragile bones. Therefore, calcium and vitamin D supplements are recommended for people with lactose intolerance.


Lactase enzyme supplements can be added to milk, as mentioned earlier, for people with lactose intolerance.

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