Time hours

Figure 4.22 The effect on plasma glucose of a 50 g test dose of lactose. The two solid lines show the range of results obtained for 10 of the subjects; the dotted line marked with squares shows the results for one subject, Ahmed L.

Table 4.3 Lactose intolerance in different population groups

Population group or country of study

Per cent lactose intolerant

UK white

Northern Germany*

Tuareg (nomads of the central Sahara)

Western Austria*

Southern Germany*

Eastern Austria*

US black


Sri Lankan



South African black Japan

Singapore-born Chinese Canadian-born Chinese Papua New Guinea

4.7 7.5 12.7 15.0 23.0 25.0 26.2 71.2 72.5 75.0 75.0 78.0 89.0 92.4 97.9 98.0

*The populations of eastern and western Austria are of different origin, as are the populations of northern and southern Germany.

adulthood, and become progressively lactose intolerant. Frequently, they present with a history of abdominal discomfort and diarrhoea. Careful questioning may reveal that this occurs especially after drinking milk, but commonly it is necessary to test their response to a test dose of lactose. As noted above, the classical method was to give a 50 g dose of lactose and measure the glycaemic response — Ahmed L suffered considerable discomfort during this test.

A number of workers have used measurement of hydrogen in exhaled air after a small test dose of lactose as a less unpleasant way of detecting lactose intolerance. Can you explain how measuring breath hydrogen can give information about lactose digestion?

A number of studies have been performed to determine lactose tolerance in adults from different populations; some of the results are shown in Table 4.3. What conclusions can you draw from the results in Table 4.3?

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