Lactose intolerance is a common condition in which the body cannot adequately digest lactose. It is usually caused by a lactase deficiency in the small intestine, where the enzyme lactase is either absent or produced in insufficient quantities. Without enough of this enzyme, lactose is not broken down into glucose and galactose and is not properly absorbed. Instead, the lactose reaches the large intestine, where gut bacteria break it down, producing gas.
Typical symptoms of lactose intolerance include bloating, abdominal pain, and diarrhea after consuming milk and dairy products. Symptoms often occur hours after consuming foods containing lactose. People with lactose intolerance can often tolerate small amounts well, while larger amounts of lactose trigger noticeable symptoms of lactose intolerance.
Definition: What is lactose intolerance?
Lactose intolerance is also known as milk sugar intolerance. It is a food intolerance to milk sugar (lactose) caused by an enzyme deficiency. The body lacks the enzyme lactase. As a result, it is unable to digest the lactose that occurs naturally in milk and dairy products.
As a result, people with lactose intolerance experience symptoms after consuming milk and dairy products such as
- powdered milk,
- cheese,
- yogurt,
- quark,
- cream,
- ice cream, or
- chocolate
Symptoms such as
- bloating,
- nausea,
- stomach pain, and
- diarrhea
.
Milk sugar (lactose) is a disaccharide. It is normally broken down by lactase into its two components, glucose and galactose. It can then pass through the intestinal wall into the bloodstream.
Lactase is produced in the lining of the small intestine. If the small intestine produces too little or no lactase at all, this breakdown of lactose does not occur or occurs only to a limited extent.
However, the small intestine cannot absorb undigested lactose. As a result, some of the lactose remains in the small intestine, where it binds water and thus causes diarrhea.
On the other hand, it continues into the large intestine, where it is converted by bacteria into
- lactic acid,
- acetic acid,
- carbon dioxide, and
- hydrogen
, which leads to the bloating typical of lactose intolerance.
Prevalence of Lactose Intolerance
The prevalence of lactose intolerance varies from region to region. In Germany, estimates suggest that about 15 percent of people suffer from lactose intolerance to a greater or lesser degree. Lactose intolerance is also common in other European countries as well as in the United States.
Lactose intolerance is particularly widespread in Asian countries and sub-Saharan Africa. Here, about 90 percent of people lack lactase, the enzyme needed to digest lactose.
Causes of Lactose Intolerance
Lactose intolerance is always caused by a deficiency of the enzyme lactase in the small intestine lining.
There are two forms:
- Primary lactase deficiency is genetic
- secondary lactase deficiency is acquired over the course of a person’s life
In the primary form of lactose intolerance, the lactase deficiency is present from birth—though this is very rare. Far more commonly, it gradually worsens over the course of a person’s life.
Secondary lactose intolerance develops
- as a result of gastrointestinal disorders, such as chronic inflammatory bowel diseases, or
- as a result of medical treatment, such as after gastrointestinal surgery or after prolonged use of medications like antibiotics or cytostatics.
Symptoms of lactose intolerance
The symptoms of lactose intolerance usually appear within a few hours of consuming milk and dairy products.
Typically, lactose intolerance causes symptoms such as
- cramp-like abdominal pain,
- bloating,
- loud bowel sounds,
- a feeling of fullness,
- diarrhea,
- constipation,
- a strong urge to have a bowel movement,
- nausea, and
- vomiting.
Nausea and gastrointestinal discomfort are common symptoms after consuming dairy products in people with lactose intolerance © bit24 | AdobeStock
However, atypical symptoms not related to the digestive tract can also occur in cases of lactose intolerance. These include, among others,
- headaches,
- dizziness,
- fatigue,
- exhaustion,
- limb pain, or
- skin problems such as acne.
The severity of the symptoms depends on
- whether the person has mild or severe lactose intolerance and
- how much lactose-containing food they have consumed.
For example, some people can tolerate at least small amounts of lactose without developing symptoms. Others are symptom-free only if they completely avoid lactose.
Diagnosis of Lactose Intolerance
To diagnose lactose intolerance,
- the self-test,
- the H₂ breath test, and
- the lactose tolerance test
are available for diagnosing lactose intolerance.
For the self-test, the person first avoids dairy products for a few days and then drinks a glass of milk. If typical symptoms such as abdominal pain or diarrhea occur immediately afterward, lactose intolerance is suspected. If the symptoms disappear after three to four weeks without consuming dairy products, the diagnosis is virtually certain.
The most widely used test for diagnosing lactose intolerance is the H2 breath test (H2 = hydrogen). During the breakdown of lactose, gases are produced, including colorless and odorless hydrogen. Its concentration in the exhaled breath is measured at various time intervals before and after ingesting a lactose solution. In addition, the patient is observed for diarrhea or signs of bloating.
Another method for diagnosing lactose intolerance is the lactose tolerance test. In this test, the patient is also given a lactose solution. A blood test is then performed to measure the amount of glucose (broken-down lactose) in the blood. If the level is too low, it is likely that the patient has lactose intolerance.
Treatment of Lactose Intolerance
Lactose intolerance is usually treated by switching to a low-lactose or lactose-free diet. Those affected should therefore largely or completely avoid consuming milk or dairy products.
Instead, they should opt for lactose-free or lactose-reduced foods. Suitable options include soy products or lactose-free dairy products. With the latter, there is no difference in taste except for a slightly sweet flavor. This sweet taste results from the industrial removal of lactase.
Those who completely avoid dairy products should take calcium supplements if necessary to prevent potential deficiency symptoms.
In addition, for people with lactose intolerance, taking lactose in the form of a dietary supplement can be helpful. The missing enzyme is available in liquid or tablet form. It can be taken before a meal containing milk or added to the milk.
If the lactose intolerance is secondary, it is important to treat the underlying condition.
Prognosis for Lactose Intolerance
Lactose intolerance is often a chronic condition and is usually incurable. However, it is not life-threatening. Life expectancy is not reduced by lactose intolerance.
Those affected should, however, prepare for a lifelong low-lactose or lactose-free diet. If this diet is consistently followed, most people with lactose intolerance can lead a symptom-free life.
FAQ
What are the typical symptoms of lactose intolerance?
Typical symptoms of lactose intolerance include bloating, abdominal pain, diarrhea, and general discomfort after a meal containing lactose. Symptoms usually occur hours after consuming foods containing lactose. Symptoms such as bloating are caused by gases formed in the large intestine.
How does lactose intolerance develop?
Lactose intolerance results from a lactase deficiency, in which the enzyme lactase cannot break down lactose sufficiently. Normally, lactose is broken down into glucose and galactose and absorbed in the small intestine. In primary lactose intolerance, lactase production decreases over the course of a person’s life, while secondary lactose intolerance can be triggered by a disease of the intestinal mucosa, such as celiac disease.
How is the diagnosis made?
If lactose intolerance is suspected, the diagnosis is often made using a hydrogen breath test. In this test, the hydrogen levels in the breath are measured after consuming a specific amount of lactose. If these levels rise, this indicates lactose intolerance.
Which foods should be avoided?
People with lactose intolerance should primarily reduce their intake of milk and dairy products that are high in lactose. These include traditional dairy products such as milk and yogurt, as well as certain processed foods containing lactose. Lactose-free products are generally well tolerated and improve daily quality of life.
How is lactose intolerance treated?
Treatment for lactose intolerance involves an adjusted diet. A low-lactose or lactose-free diet helps prevent the typical symptoms. In addition, a supplement containing the enzyme lactase can be taken before consuming dairy products to aid digestion.
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About the medical author
Dr. Claus Puhlmann
Medical Author · Medical journalist
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