Gastrointestinal Lactose Test


Genetics and Milk Digestion

Milk has been called "the almost perfect food", rich in proteins, vitamins, minerals and other nutrients. Therefore, it is surprising that those who cannot digest milk sugar make up the majority of the world’s population! Any adult fortunate enough to be able to drink milk without getting sick belongs to a biological minority: they are limited to a portion of white North Americans, Australians, Northern Europeans, and three African tribes-the Fulani, the Hima and the Tussi.

Have you ever tried to order milk in an authentic Chinese restaurant that caters largely to Chinese clientele, or to find an authentic Chinese recipe which contains milk? You probably failed in both efforts. Most Chinese adults do not drink milk because they can not fully digest it. The Chinese, and others who cannot digest milk sugar (lactose), do not have a lactase enzyme. All babies (including Chinese, of course) have the enzyme until they are about three years old; after which they gradually lose the ability to manufacture the enzyme. Some groups have learned to use nature to destroy the lactose in milk; for instance, an African tribe which is a lactase non-producer consumes a highly-fermented yogurt, called nono, which has soured in the sun and lost its milk sugar, and many natives of India include yogurt in the diet, because it has lost much of its lactose in the fermentation process.

The lactase enzyme is produced in a segment of the small intestine called the jejunum. As milk is carried through the jejunum, the lactase enzyme latches onto the milk sugar and splits it into two components, glucose and galactose, which are absorbed into the blood and broken down or stored by the liver. When the jejunum can no longer manufacture the lactase enzyme, lactose passes through the small intestine to the colon where it is fermented by bacteria. Depending on the lactose load and the severity of the lactase enzyme deficiency, when it is fermented, lactose gives off acids, carbon dioxide and hydrogen and can induce everything from an unpleasant distention to bloating, cramps and watery, explosive diarrhea.

The question of why most Northern Europeans can drink milk and many of those in the Middle East or the Orient cannot has stimulated research in anthropology, geography, sociology, genetics and biochemistry. Does a constant diet of milk stimulate the continued production of lactase beyond the age of three? Or, is milk tolerance an inherited trait like brown skin or blonde hair? The answer to these questions has come from studies of mixed marriages (between lactose tolerant and lactose intolerant individuals). The ability to digest milk sugar beyond childhood is passed along genetically and is a dominant trait. Thus, if a child inherits a gene for lifelong milk tolerance from one parent and a gene for milk intolerance from the other parent, the child will be milk tolerant.

Given the evidence that milk tolerance is an inherited characteristic, why is the gene prevalent in some cultures and not in others? Why is the gene present in a few African tribes, but largely absent throughout the rest of the continent? Scientists believe that man originally evolved without the capacity to digest milk sugar beyond the period of weaning; for 100 million years we were not different from other mammals. However, about 9,000 B.C. man began domesticating animals such as goats, sheep and cattle, and sometime after that started milking the animals. For instance, the nomadic African tribe, the Fulani, were one of those dairying cultures. A few individuals in the tribe presumably had a mutant gene which produced lactase into adulthood and found that they could drink milk without ill effects. The selective nutritional advantage which was conferred on them by a diet which included milk, gave them greater vigor and better health and permitted them to multiply faster and more successfully defend their families. Over the course of thousands of years, the milk drinkers became the dominant members of the Fulani. A similar genetic history presumably accounts for the high incidence of lactase producing genes in Northern European descendants, as well.

Within the last decade an accurate, easy-to-use test has been developed to identify individuals with complete or partial inability to digest lactose. This noninvasive test measures trace concentrations of hydrogen in the air expired from the lungs after a person has drunk a glass of liquid lactose. Hydrogen will be produced by the fermentation of lactose in the colon of an individual who is a lactase non-producer, and will appear in the "alveolar air" after the undigested milk sugar gets to the colon. A few individuals (5-10% of those who are lactose malabsorbers) produce methane instead of hydrogen when lactose is fermented. They are identified as non lactase producers who do not produce hydrogen, by testing with "lactulose", a sugar which is not normally digested and will produce hydrogen unless conditions in the colon are unsuitable for the test to be applied. If the patient does not produce hydrogen from lactulose, he/she would also be unable to produce hydrogen from lactose. These conditions include recent exposure to antibiotics, severe diarrhea prior to the test and conditions which change the acidity of the colon contents. Thus, although the breath-hydrogen test is not infallible, it is the most reliable and the only "non-invasive" test available.



Ethnic Group % Intolerant Ethnic Group % Intolerant Ethnic Group % Intolerant
African Blacks 97~100 Oriental 90~100 N.A. Indians 8~90
Dravidian Indians 9~100 Mexicans 70~80 S.A. Indians 70~90
Mediterraneans 6~90 Jews 60~80 N.A. Blacks 7~75
North/Central India 25~50 NW India 3~15 N.A. Caucasians 7~15
Middle Europeans 10~20 N. Europeans 1~5 Pakistan 3~15

The benefits of breath testing

What is the justification for a breath-hydrogen test for lactose malabsorption, since the diagnosis can apparently be made by simply removing milk ( and milk products ) from the diet and looking for a change in the patient's symptoms?

There are at least 4 reasons why simply withholding milk from the diet is an imprecise and inadequate approach to the diagnosis of carbohydrate malabsorption:

  • The simplistic approach of withholding milk from the diet as a diagnostic test will be unequivocal only with those patients who are so obviously intolerant that they will probably know it, anyway. Even then, the answer is incomplete, since the procedure provides no evidence as to whether or not total avoidance of milk products is necessary for the relief of symptoms.
  • Recently, it has become clear that many marginally intolerant patients are not suspected of having lactose intolerance until it is identified by the breath-hydrogen test. As reported, at the meetings of the AGA in San Francisco in May, 1986, and in Chicago in 1987 ( References below ), many patients were unsuspected lactose malabsorbers. Results from the test enabled patients to associate symptoms with lactose ingestion, which led to improvement after its restriction. Without the breath-H2 test, the relationship may be difficult to establish, and it may be difficult to convince the doubting patient to conscientiously avoid milk products during the test.
  • When the test is properly performed, the breath-H2 response provides a general guide as to the severity of the malabsorption. It is useful to have at least semi-quantitative data which suggest how severe the lactose malabsorption might be. Therefore, the test can be a guide for recommending the level at which milk or milk products can be included in the diet. Total avoidance may be unnecessary burden for some patients and a threat to health unless supplemental calcium is added to their diets.

Irritable Bowel Syndrome & Bacterial Overgrowth Testing:

The symptoms of irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO) are very similar: abdominal pain, cramping, diarrhea, constipation and bloating. A recent study strengthens the hypothesis that treating bacterial overgrowth will frequently alleviate the symptoms of IBS, the most common gastrointestinal diagnosis in the United States. This study was published in The American Journal of Gastroenterology in November of 2000 by Dr. Mark Pimentel, et. al., and concluded that small intestinal bacterial overgrowth is associated with irritable bowel syndrome, and that eradication of the overgrowth eliminates IBS by study criteria in 48% of subjects.1

The breath test for bacterial overgrowth is a simple, non-invasive procedure that may lead to a specific course of treatment and relief for some patients experiencing the distress of irritable bowel syndrome. It is recommended that breath tests be given before antibiotic therapy is administered as to not unnecessarily dispense antibiotics. A breath test is also used to confirm eradication of SIBO

Methane and Lactose Malabsorption Tests

When bacteria metabolize (or ferment) carbohydrates, they produce acids, water and gases. The major gases include carbon dioxide (CO2) and hydrogen (H2). early half of H2-producers also produce methane (CH4). Furthermore, CH4 production has been identified in those who fail to produce H2 following ingestion of non-digestible sugars. pattern of gas production is related to the type of bacteria resident in the colon and can not be predicted in advance. However, most reports suggest that a significant percentage of malabsorbers will be missed if breath-methane is not measured during the lactose malabsorption test.

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