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ANTB15- Lactose- Dec 2- lec 11.docx

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Larry Sawchuk

Lactose- December 2, 2013- Lecture 11 Milk  Food Value: Lactose aspect of fresh milk – valuable source of nutrition  Calcium for growth  Water Content: Milk provides extra fluid and is a water source (particularly important in arid regions, e.g., desert nomads Dietary Variation via the Animal Milked: Not Directly Interchangeable All are MAMMALS; all have LACTOSE component, but in varying quantities Unusual about human’s source of milk: high lactose Calcium & Bone  20 century: the problem addressed through diet supplementation - vitamin D added to milk (OK – as long as you are lactose tolerant… -Vitamin D facilitates the absorption of calcium - This supplement was added in the 1900s Lactase Activity: Genetic Polymorphism  Suspected result of:  Single dominant mutation with high penetrance (high proportion of those with the mutation showing signs/symptoms of lactase persistence) Penetrance: You have the gene, but you don’t express it What is Lactose Intolerance?  Inability to break down LACTOSE, the sugar found in dairy products (milk)  Inability stems from lack of LACTASE – an enzyme produced by cells in the small intestine What does lactase do?  LACTASE – breaks down milk sugar lactose into simpler forms of sugar (glucose and galactose) which can then be absorbed into the bloodstream Lactose Intolerance Symptoms  Considerable individual variation in lactose intolerance  Symptoms of abdominal pain, bloating gas (flatulence) and cramps, nausea, diarrhea arise because: Lactose Intolerance Symptoms  Lactose is not being broken down (into glucose) & is left unabsorbed  In the small intestines: lactose stimulates osmotic transport of water into the small intestine (watery stool), and…  When further passed along to COLON:  Lactose is fermented by action of colon bacteria  Leads to formation of gases – methane and carbon dioxide  Cause the intestines to inflate & result = pain (cramps) and flatulence Lactose Intolerance  Among some people - ability to digest lactose (milk sugar) declines rapidly after weaning  Falling levels of the enzyme lactase in the small intestine (turned ‘off’ about 4 yrs of age) Commonly pathway found in all mammals – may actually serve as stimulus encouraging weaning, except that…. Weaning: trying to take the child off of breast milk and onto artificial foods -> there’s a different gene during infancy , and most of us have that gene. That gene breaks down milk sugar, until 2-3, max 4 years of age. - Everybody can digest milk as a baby - Around age 4, EVERYONE loses that ability - There are some people who have congenital absence of this particular gene and they cannot digest the mother's milk (present at birth); so that gene switches off - Adult gene: switching on, for some populations, and for some, it never switches on - At 6 months of age: when most human beings wean their children (there are other situations when it becomes uncomfortable for mothers to breast feed, such as when the baby gets their primary teeth Lactase Persistence  Large number of people worldwide, however, with lactase activity that persists into adulthood  Initial definition of disease state as those unable to digest lactose (i.e., the lactose intolerant) = Eurocentric viewpoint, so… ‘tolerance’ – orig
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