Introduction to Human Nutrition

76 Introduction to Human Nutrition

mutation in SGLT1 is responsible for the very rare

glucose–galactose malabsorption syndrome, but such

individuals absorb fructose well. In up to 60% of

adults, the capacity for facilitated diffusion of fructose

appears to be limited, resulting in symptoms of

“intestinal distress” when challenged by consumption

of 50 g fructose.

5.3 Glycemic carbohydrates

The rate of uptake of glucose (and other sugars) from

the gut is determined by the rate of hydrolysis of oli-

gosaccharides and polysaccharides that are suscepti-

ble to pancreatic and brush border enzymes. In addi-

Table 5.2 tion to the primary structure of the polymers, many

Carbohydrate composition (g/100 g) of some vegetable dishes

Dish

Water

Carbohydrate

Starch

Total sugars

Glucose

Fructose

Galactose

Sucrose

Maltose

Lactose

Oligosaccharides

NSPs

Cellulose

Bhaji, okra

77.7

7.6

0.4

5.5

1.9

1.7

0

1.9

0

Tr

1.7

3.2

1.0

Cannelloni, spinach

73.4

12.6

10.4

2.2

0.1

0.1

0

0.1

0.1

1.7

Tr

1.2

0.8

Chili, beans and lentils

72.6

13.1

7.9

4.3

1.3

1.4

0

1.6

0

0

0.8

3.6

1.1

Curry, chickpea

52.7

21.3

18.7

1.2

Tr

0.1

0

1.0

0

0

1.4

4.5

1.1

Flan, cheese and mushroom

49.1

18.7

16.4

2.3

0.2

0.2

0

0.1

Tr

1.8

Tr

0.9

0.1

Pizza, cheese and tomato

51.0

25.2

23.0

2.2

0.6

0.6

0

0.9

0.1

Tr

0

1.4

0.2

Shepherd’s pie, vegetable

71.7

15.8

14.0

1.4

0.5

0.4

0

0.6

0

0

0.4

2.4

0.8

Data from Holland

et al.

(1992). Reproduced with permission from HMSO.

NSPs, nonstarch polysaccharides (Englyst method; Englyst

et al.

1999); Tr, trace.

Gut

lumen

Fructose Na

Fructose

Fructose

GLUT5

SGLT1

GLUT2

Na/K-ATPase

Glucose

and

galactose

Glucose

and

galactose

Glucose and

galactose

Tight

junction

Na

Na

K

K

ATP

ADP



Pi

Apical

membrane

Basolateral

membrane

Blood

Figure 5.1 Sugar transporters on enterocytes, showing the transport

of glucose and galactose across the apical membrane.