Lecture 3-Digestion and Absorption of Macronutrients: page 2

Lecture 3 page 1 2 3 4 5

Absorption (figure 1)

Glucose uptake is Na+ dependent
Fructose is absorbed via facilitated diffusion
Galactose and glucose are actively transported
1. SGLT1 is the transport protein responsible for Na+ dependent glucose transport 2. Glut-2 transports glucose out of the cell into the portal circulation 3. Also transports galactose and fructose 4. A high CHO diet increases SGLT1 and Glut-2 levels 5. SGLT1 mRNA and protein are increased in diabetes mellitus

Figure 1
Enterocyte transport of monosaccharides

(Johnson LR, ed. Physiology of the Gastrointestinal Tract. Raven Press, NY, 1994. pp. 1751-1772)

Galactosemia
An inborn error of metabolism (autosomal recessive trait) manifested as failure to thrive in newborn children due to anorexia, vomiting and diarrhea when milk or sugar water is ingested

Lactose intolerance (table 1)
Lactase activity diminishes to 10% of neonatal level by age 5-10
Sx: abd pain, cramping, distention, flatulence, diarrhea, possible nausea and vomiting

Lactose draws water into the intestinal lumen and produces osmotic diarrhea. Gut flora metabolizes the lactose forming gases such as hydrogen, methane, and carbon dioxide.

Table 1 Prevalence of late-onset lactose malabsorption
among various ethnic and racial groups

Group	Prevalence of lactose malabsorption (%)
Asians in the United States	100
American Indians (Oklahoma)	95
Ibo and Yoruba (Nigeria)	89
Black Americans	81
Italians	71
Aborigines (Australia)	67
Mexican Americans	56
Greeks	53
White Americans	24
Danes	3
Dutch	0
(From Buller HA, Grand RJ.Lactose Intolerance.Annu Rev Med. 1990;41:141-148.)

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Lecture 1:Introduction to Nutrition in Western Civilization
Lecture 2: Dietary Macronutrients, Body Fat, and Blood Lipids
Lecture 3:Digestion and Absorption of Macronutrients
Lecture 4:Basic Principles of Nutrient Metabolism
Lecture 5:Obesity
Lecture 6:Fuel Utilization During Exercise
Lecture 7:Biochemistry of Oxidant Stress in Health and Disease Antioxidants
Lecture 8:Nutrition for the 21st Century

Nutrition 101 - Natural Remedies - Weight Management - Physician Education
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