Chemistry Reference
In-Depth Information
gut wall, which results in a large influx of water to redress the osmotic
imbalance, causing symptoms of diarrhoea. Second, the lactose can be uti-
lised as an energy source by colonic bacteria, which ferment it to produce
fatty acids and gaseous by-products, potentially causing discomfort, bloating
and flatulence.
Most lactase non-persistent individuals can tolerate small amounts of lac-
tose (as contained in the milk added to tea or coffee). Diarrhoea and discomfort
are not seen in all individuals who are diagnosed as lactose maldigesters in a
lactose tolerance test, even after consumption of 50 g of lactose, and it has been
suggested that variation in the composition of the gut flora between individuals
may be responsible for some of this variation (Hertzler and Savaiano, 1996;
Hertzler et al., 1997), as well as a psychosomatic component (Briet et al., 1997).
In contrast, two separate studies suggest that around 40% of self-diagnosed
lactose malabsorbers are actually lactose digesters (Saltzman et al., 1999; Peuhkuri
et al., 2000). This effect is perhaps due to prevalence in the public consciousness of
'dairy intolerance' caused by extensive media coverage of the condition, leading
individuals to assign any symptoms of gastrointestinal discomfort to this cause.
The symptoms described above were first attributed to a lack of lactase
following the observation that a proportion of intestinal tissue samples from
healthy adults with histologically normal mucosa had virtually no lactase
activity (Auricchio et al., 1963; Dahlqvist et al., 1963). The discovery of this
enzyme deficiency or 'abnormality' in humans ignited the interest of research-
ers into the inter-individual differences in our capacity to tolerate milk and its
derived dairy products. In the following years, data on lactase persistence
frequencies in other populations began to accumulate and a global picture
began to develop that challenged the original perception of lactase non-
persistence as the 'abnormal' phenotype.
6.4.
Diagnosis of Lactase Non-Persistence/Persistence
In order to collect information on the worldwide frequencies, alternatives to
direct quantification via biopsy of the small intestine were used. Biopsies are
the most accurate method for establishing lactase activity. However, they are
invasive and are not usually a preferred routine diagnostic for lactose intol-
erance, normally being obtained only when a patient is undergoing endo-
scopy to exclude another gastrointestinal complaint.
Several indirect methods have been developed for the purpose of diag-
nosis, all of which utilise lactose digestion to inform on an individual's lactose
tolerance status, and by implication lactase persistence status. The general
practice is to give a lactose load after an overnight fast. The two most widely
used methods are described below.
