Lactose intolerance Totally Explained

Everything about Lactose Intolerance totally explained

Lactose intolerance is the inability to metabolize lactose, a sugar found in milk and other dairy products, because the required enzyme lactase is absent or its availability is lowered. It is estimated that 70% of adult humans are lactose intolerant.

Overview

Disaccharides can't be absorbed through the wall of the small intestine into the bloodstream, so in the absence of lactase, lactose present in ingested dairy products remains uncleaved and passes intact into the colon. The operons of enteric bacteria quickly switch over to lactose metabolism, and the resultant in vivo fermentation produces copious amounts of gas (a mixture of hydrogen, carbon dioxide, and methane). This, in turn, may cause a range of unpleasant abdominal symptoms, including stomach cramps, bloating, and flatulence. In addition, as with other unabsorbed sugars (such as sorbitol, mannitol, and xylitol), the presence of lactose and its fermentation products raises the osmotic pressure of the colon contents, thereby preventing the colon from reabsorbing water, and causing osmotic diarrhea.

Classification

There are three major types of lactose intolerance:

Primary lactose intolerance. Environmentally induced when weaning a child in non dairy consuming societies. In such cases the production of lactase may be permanently disrupted. A very common cause of temporary lactose intolerance is gastroenteritis, particularly when the gastroenteritis is caused by rotavirus. Another form of temporary lactose intolerance is lactose overload in infants.
Congenital lactase deficiency. A genetic disorder which prevents enzymatic production of lactase. Present at birth, and diagnosed in early infancy.

Lactase biology

The enzyme lactase, also called beta-D-galactosidase, is synthesized if at least one of the two genes for it are present. Only when both gene expressions are affected is lactase enzyme synthesis reduced, which in turn reduces lactose digestion.. Lactase persistence, allowing lactose digestion to proceed, is the dominant allele. Physiological lactose intolerance, therefore, is an autosomal recessive trait.
   However, cultures such as that of Japan, where dairy consumption has been on the increase, demonstrate a lower prevalence of lactose intolerance in spite of a genetic predisposition.
   The normal mammalian condition is for the young of a species to experience reduced lactase production at the end of the weaning period (a species-specific length of time). In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely. However, certain human populations have a mutation on chromosome 2 which results in a bypass of the common shutdown in lactase production, making it possible for members of these populations to continue consumption of fresh milk and other dairy products throughout their lives.
   Pathological lactose intolerance can be caused by Coeliac disease, which damages the villi in the small intestine that produce lactase. This lactose intolerance is temporary. Lactose intolerance associated with coeliac disease ceases after the patient has been on a gluten-free diet long enough for the villi to recover.
   Certain people who report problems with consuming lactose are not actually lactose intolerant. In a study of 323 Sicilian adults, Carroccio et al. (1998) found only 4% were both lactose intolerant and lactose maldigesters, while 32.2% were lactose maldigesters but didn't test as lactose intolerant. However, Burgio et al. (1984) found that 72% of 100 Sicilians were lactose intolerant in their study and 106 of 208 northern Italians (for example, 51%) were lactose intolerant.

Lactose intolerance by group

Further Information

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