BIBC 120 Lecture Notes - Lecture 9: Lactose Intolerance, Dietary Fiber, Lactase
24 May 2018
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Week 3.3
LACTASE PERSISTENCE AND LACTOSE INTOLERANCE
- Why is lactose the carbohydrate present in milk?
o not many organisms have enzyme to break down b1,4 bonds
o foods with glucose can be spoiled quickly by bacterial growth (mostly which can
digest glucose as an energy source to grow)
- All mammals express lactase during infancy to allow them to digest milk during nursing
- Lactase expression rapidly declines upon weaning, leaving adult mammals unable to
break down lactose
o Humans are the exception; 1/3 of the world is lactase persistent (continual
lactase expression through adulthood)
▪ Lactase Persistence: Some human populations evolved the continued
expression of lactase through adulthood
▪ high frequency of lactase persistence from northern European descent
(75-90) Scandinavia has the biggest amount of lactase persistence
▪ Asian (0-20), African, native American (0) have almost no lactase
persistence
o What could be the evolutionary advantage to extending lactase expression
through adulthood?
▪ Humans domesticated herd animals (cattle, goats, sheep) around starting
around 11,000 years ago in southwest Asia
▪ The evolution of lactase persistence alleles is probably linked to the
importance of consuming milk in those populations, pastoral populations
(i.e. Bedouin in Jordan)
- Alleles for lactase persistence are thought to have independently arisen multiple times
o Caucasus Mountains of central Europe (approx. 7500 years ago)
o Saudi Arabia
o East Africa
- Genetics of Lactase Persistence
o Autosomal
o Persistence phenotype is dominant over non-persistence phenotype
o Heterozygotes (for persistence allele of gene) tend not to be lactose intolerant
- Lactobacillus bacteria (have lactase) consume lactose in the preparation of fermented
food products: Cheese and yogurt
o lactose → glucose ----(glycolysis)---> lactate
o removes a lot of the lactose
o may be alternative to lactase persistence
Lactose Intolerance
- Lactose reaches the large intestine where bacteria metabolize it through fermentation
- Fermentation by-products (including CO2) can produce symptoms such as abdominal
cramping, flatulence, and sometimes diarrhea
- There is a large range in the severity of the symptoms
- Lactose intolerance is strongly linked to lactase persistence vs. lack of persistence, but
the correlation is not absolute
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Document Summary
All mammals express lactase during infancy to allow them to digest milk during nursing. Alleles for lactase persistence are thought to have independently arisen multiple times: caucasus mountains of central europe (approx. 7500 years ago: saudi arabia, east africa. Genetics of lactase persistence: autosomal, persistence phenotype is dominant over non-persistence phenotype, heterozygotes (for persistence allele of gene) tend not to be lactose intolerant. Lactobacillus bacteria (have lactase) consume lactose in the preparation of fermented food products: cheese and yogurt lactose glucose ----(glycolysis)---> lactate: removes a lot of the lactose, may be alternative to lactase persistence. Lactose reaches the large intestine where bacteria metabolize it through fermentation. Fermentation by-products (including co2) can produce symptoms such as abdominal cramping, flatulence, and sometimes diarrhea. There is a large range in the severity of the symptoms. Lactose intolerance is strongly linked to lactase persistence vs. lack of persistence, but the correlation is not absolute.
