Lactose intolerance

From Freepedia

Lactose intolerance
ICD-10 code:	E73
ICD-9 code:	271.3

Lactose intolerance is the condition in which lactase, an enzyme needed for proper metabolization of lactose (a constituent of milk and other dairy products), is not produced in adulthood. With lactose intolerance, the result of consuming lactose or a lactose-containing food is excess gas production and often diarrhea. In western cultures milk products are nearly ubiquitous and are contained in at least a small amount in almost all recipes, restaurant dishes, and processed food. People with lactose intolerance need to be very careful reading food ingredient labels if they wish to avoid consuming lactose.

1 Biology
- 1.1 Lactose intolerance by group
2 Etiology
3 Diagnosis
4 Treatment
5 History
6 See also
7 External links
8 References

Biology

The normal mammalian condition is for the young to lose the ability to effectively digest milk sugar (lactose) at the end of the weaning period (a species-specific length of time usually equal to roughly 3% of lifespan). In humans, lactase production usually drops about 90% during the first four years of life, though the exact drop and age varies widely. However, certain human populations have undergone a mutation on chromosome 2 which results in a bypass of the normal shutdown in lactase production, allowing members of these groups to continue consumption of fresh milk and fresh milk products throughout their lives.

There is some debate on exactly where and when the mutation(s) occurred, some arguing for separate mutation events in Sweden and the Arabian Peninsula near 4000 BC which converged as they spread, while others argue for a single event in the Middle East at about 4500 BC which radiated from there. Some sources suggest a third and more recent mutation in the East African Tutsi. Whatever the precise origin in time and place, most modern western Eurasians and people of western Eurasian ancestry show the effects of this mutation (that is, they are able to safely consume milk products all their lives) while most modern eastern Eurasians, sub-saharan Africans and native peoples of the Americas and Pacific Islands do not (making them lactose intolerant as adults)[1].

Lactose intolerance by group

Human groups	Individuals Examined	Percent Intolerant	Allele Frequency
Swedish	NA	2%	0.14
Europeans in Australia	160	4%	0.20
Swiss	NA	10%	0.316
American Caucasians	245	12%	0.346
Finns	134	18%	0.424
African Tutsi	NA	20%	0.447
African Fulani	NA	23%	0.48
African Americans	20	75%	0.87
Australian Aborigines	44	85%	0.922
African Bantu	59	89%	0.943
Chinese	71	93%	0.964
Thais	134	98%	0.99
American Indians	24	100%	1.00

Table Data obtained (in part) from "Lactose and Lactase", Scientific American, October, 1972, by Norman Kretchmer. Statistical significance varies greatly depending on number of people sampled.

Etiology

Without lactase, the lactose in milk remains uncleaved and unabsorbed. Lactose cannot pass easily through the intestinal wall into the bloodstream, so it remains in the intestines. Soon, gut bacteria adapt to the relative abundance of lactose (relative to other sugars like glucose) and switch over to metabolizing lactose. Along the way they produce copious amounts of gas by fermentation.

The gas causes a range of unpleasant abdominal symptoms, including stomach cramps, bloating, flatulence and diarrhea. Like other unabsorbed sugars, e.g. mannitol, the lactose raises the osmotic pressure of the colon contents, preventing the colon from resorbing water and hence causing a laxative effect to add to the excessive gas production.

Diagnosis

Since the majority of Europeans have the mutation rendering them lactose-tolerant, lactose intolerance is widely regarded as a medical condition in Europe and North America. A fair proportion of patients with symptoms of irritable bowel syndrome actually have lactose intolerance without knowing it.

A simple test can clarify the issue: after an overnight fast, 50 grams of lactose (in a solution with water) is to be swallowed. If the lactose cannot be digested, enteric bacteria will metabolize it and produce hydrogen. This can be detected in the air the patient exhales. The test takes about 2 to 3 hours. A medical condition with similar symptoms is fructose malabsorption.

Although not as precise a test, an estimate of lactose intolerance can be made as follows: Drink two cups of milk on an empty stomach and watch for signs of intestinal discomfort over the next several hours. The following day, eat two ounces of hard cheese. If symptoms are experienced only on the first day, the individual may be lactose intolerant. If symptoms are experienced on both days, the individual may have an allergy to dairy products.

Some individuals are able to self-diagnose without intentionally testing themselves, simply by realizing in retrospect that their symptoms always correspond to prior lactose consumption. This, however, is the least reliable of the methods herein described, as peoples' memories are imperfect. In addition, it is harder to isolate one definite cause without a formal test.

Treatment

One solution to this problem (other than avoiding milk) is lactose-free milk, which is produced by passing milk over lactase enzyme bound to an inert carrier: once the molecule is cleaved, there are no lactose ill-effects, whatever the milk drinker's ancestry. Alternatively, a harmless bacterium such as L. acidophilus may be added, which affects the lactose in milk the same way it affects the lactose in yogurt (see below). The milk sold for pet cats is another example of lactose-reduced milk. Oddly, many European cat breeds have a mutation similar to the human mutation, also prevalent in Europe, which allows symptom-free adult lactose consumption. Most Asian breeds are particularly sensitive to lactose.

Lactose intolerance is not all or nothing: the amount of lactose that can be tolerated varies from person to person, and decreases with age. According to the National Institute of Health, "Dietary control of lactose intolerance depends on people learning through trial and error how much lactose they can handle."NIH

Many people are more tolerant of yogurt than milk because it contains lactase produced by the bacterial cultures used to make the yogurt. Also, hard cheeses (e.g. Swiss) produce far less reaction than the equivalent amount of milk because the cheesemaking and aging processes greatly reduce the amount of lactose. A typical Swiss or Cheddar might contain 5% of the lactose found in whole milk, while long-aged cheeses contain almost no lactose at all.[2]

In recent years (1990–2000) there has been an increase in the number of lactose-reduced and lactose-free dairy products. Examples of these products are cottage cheese, American cheese and ice cream. These products are made using milk substitutes such as soy milk, almond milk, or rice milk. Another recent solution has been lactase pills which provide the missing enzyme, allowing a person to tolerate milk products for about 30-45 minutes after taking a pill.

History

The condition was first recognized in the 1950s and 1960s when various organizations like the United Nations began to engage in systematic famine-relief efforts in countries outside Europe for the first time. As anecdotes of embarrassing dairy-induced discomfort piled up, the First World donor countries could no longer ascribe the reports to spoilage in transit or inappropriate food preparation at the recipient end in the Third World.

Since the first nations to industrialize and develop modern scientific medicine were dominated by people of Western and Northern European descent, adult dairy consumption was long taken for granted. Westerners for some time did not recognize that the majority of the human ethnogenetic groups could not consume dairy during adulthood. Although there had been regular contact between Europeans and non-Europeans throughout history, the notion that large-scale medical studies should be representative of the racial diversity of the human populations (and also both genders and all ages) did not become well-established until after the civil rights movements of the 1960s.

Since then, the relationship between lactase and lactose has been thoroughly investigated in food science due to the growing market for dairy products among non-Europeans.

Originally it was believe that gut bacteria such as E. coli produced the lactase enzyme needed to cleave lactose into its constituent monosaccharides and thus become metabolizable and digestible by humans. Some form of human-bacteria symbiosis was proposed as a means of producing lactase in the human digestive track; Genetics and protein analyzation techniques by the early 1970’s reveal this to be untrue and that humans produce lactase enzyme natively in intestine cells.

Approximately 70% of the global population cannot tolerate lactose in adulthood. Thus, some argue that the terminology should be reversed, lactose intolerance should be seen as the norm, and the minority Western European group should be labeled as having lactase persistence.