It is estimated that 75% of adults worldwide show some decrease in lactase activ
ID: 89640 • Letter: I
Question
It is estimated that 75% of adults worldwide show some decrease in lactase activity during adulthood (due to gene regulation). The frequency of decreased lactase activity ranges from 5% in northern Europe, to 71% in Sicily, to more than 90% in some African and Asian countries. The distribution is now thought to have been caused by recent natural selection favoring lactase-persistent individuals in cultures that rely on dairy products. Bacteria that can digest lactose exist in your gut. Lactose cannot be directly absorbed through the wall of your small intestine. First, lactose must be digested down into its two parts, glucose and galactose. If you are lactose intolerant, you do not produce an enzyme called lactase which cleaves lactose much like the beta-galactosidase enzyme in E. coli. Once you consume lactose, the bacteria in your gut will come into contact with lactose. As shown from the activities and readings above, this starts a cascade of events which results in the digestion of the lactose. Which process (of the ones discussed in Discussion 3) do the bacteria in your gut use to digest lactose? Why? To test for lactose intolerance, blood is taken from the patient every 10 to 15 minutes after ingestion of lactose. Blood glucose levels are measured for each of these time points. Why do they measure blood glucose levels instead of lactose levels? Below are blood glucose graphs from two individuals who may be lactose intolerant. Which of the graphs belongs to a patient with lactose intolerance (circle one)?Explanation / Answer
Answer:
1. Bacteria in the colon can metabolise lactose through fermentation.
When lactose isn’t absorbed in the small intestine, it passes into the large intestine. Some types of bacteria that live in the colon, called lactic acid bacteria, produce lactase. When they encounter lactose, these bacteria use their lactase to break down, then ferment, the sugars.
During fermentation, lactose is turned into lactic acid. Fermentation of lactose also produces short-chain fatty acids and gases, including methane, hydrogen and carbon dioxide. The gases are responsible for the symptoms associated with lactose intolerance, such as abdominal pain, bloating, gas and diarrhea.
2. Glucose is a product of the reaction catalyzed by lactase and therefore an indirect read-out of the enzyme’s activity.
In the lactose tolerance test, the patient consumes a lactose solution, and then a blood sample is taken to measure glucose levels.
If blood glucose levels remain the same, this indicates that glucose has not entered the blood. This is because the lactose has not been successfully broken down into glucose and galactose.
3. Graph b on the right corresponds to the patient with lactose intolerance since blood glucose levels over time is low and does not change much.
Lactose tolerant individuals have higher (and rising) levels of blood glucose (as seen in the left graph) and that lactose intolerant individuals have lower (and stagnant) levels (right graph).
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