HealthTalk: Lactose intolerance

Credit: Maria Raffaele/Art Editor Credit: Maria Raffaele/Art Editor

For some people, extra calories are not the only worrisome aspect about an occasional ice-cream or cheese indulgence. For those who are lactose intolerant, eating too much of these foods could cause severe discomfort and pain.

Within half an hour to two hours after eating lactose-containing foods, lactose-intolerant people can experience symptoms ranging from diarrhea and abdominal pain to nausea. Although the symptoms are usually mild, they can be extremely uncomfortable.

Lactose intolerance is caused by the deficiency of an enzyme called lactase, which is responsible for breaking up lactose into glucose and galactose, two different kinds of sugars. Lactose cannot be used directly by the body and needs to be broken down into these components. The small intestine is lined with cells known as microvilli, and it is these cells that normally produce lactase. The microvilli have long, thin projections on their surfaces that help absorb nutrients from the small intestine into the blood stream. After lactose is broken down into glucose and galactose in the small intestine, the sugars are absorbed into the bloodstream and used by the body.

As explained in the book Biochemistry by Jeremy Berg, John Tymoczko, and Lubert Stryer, in the absence of the lactase enzyme, lactose passes into the colon. In the colon, lactose comes into contact with healthy bacteria that are normally present there. These bacteria use the lactose as a source of energy and, to do so, convert it into lactic acid. During this reaction, methane gas and hydrogen gas are produced. These gases are responsible for the uncomfortable bloated feeling that lactose-intolerant people feel after eating dairy products. The unused lactose and the lactic acid present in the large intestine also cause water to enter the large intestine, resulting in diarrhea.

A number of different factors can lead to lactase deficiency. As explained on, lactase deficiency can be the result of the normal aging process. Lactase is produced in large amounts in babies, as their main source of nutrition is milk. However, as a person grows older and starts eating a larger variety of food, the body naturally reduces the production of lactase as it is no longer as necessary. In some people, this reduced lactase production can be more apparent and can cause symptoms of lactose intolerance. Lactose intolerance can also be caused by an injury to the small intestine. Thus, diseases such as cystic fibrosis, celiac disease, or even stomach flu can damage the cells of the small intestine and reduce lactase production. Surgical procedures involving the small intestine can also result in lactase deficiency.

For a small percentage of people, lactase deficiency can be present at birth. In such people, the gene responsible for lactase production, known as the LCT gene, is mutated. According to the Genetics Home Reference, at least nine mutations have been identified in the LCT gene resulting in a non-functional form of lactase. The inheritance of lactose intolerance is autosomal recessive, which means that both parents have to carry at least one copy of the defective gene for their child to be lactose intolerant. Babies with such a congenital form of lactose intolerance are unable to digest breast milk and require a special lactose-free infant formula.

Although lactose intolerance can be an inconvenience, major problems can be avoided by simply eating a diet free of dairy products. Chewable pills that provide the body with a supply of lactase are also available and are an easy way to deal with the condition. The body, however, gets used to the lactase pills over time, and individuals often have to continually increase the dosage of these pills to prevent symptoms of the condition.