6. glycemic index

KNOWLEDGE FOR THE BENEFIT OF HUMANITY

ADVANCED NUTRITION (HFS4352)

GLYCEMIC INDEX

Mohd Razif Shahril, PhD

School of Nutrition & Dietetics

Faculty of Medicine and Health Sciences

Universiti Sultan Zainal Abidin

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Outline

• What is Glycemix Index (GI)?

• Glycemix Index Determination Protocol

• Factors Influencing GI

• Benefits of Low GI Diet

• Take home message

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What is Glycemix Index (GI) • A scale that ranks carbohydrate by how much they

raise blood glucose levels compared to a reference food. – Developed by Jenkins et al. 1981. Am J Clin Nutr.

34(3):362-366.

• References on GI – Brand-Miller et al. 2006. The New Glucose

Revolution. 3rd ed. New York, NY: Marlowe & Co. – Written by experts on GI

– Atkinson et al. 2008. Diabetes Care 31(12):2281-2283

– Most comprehensive table of the GI of foods that has been assembled to date

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What is Glycemix Index (GI)

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Rapidly digested or absorbed carbohydrates

Slowly digested or absorbed carbohydrates

What does the GI value mean? • The glycemic index (GI) is expressed as a ratio

comparing the blood glucose increase caused by a test

food to that of a reference food (usually glucose) for 2

hours following ingestion.

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Area Under the Curve for Test Food

Area Under the Curve for Reference Food × 100 = GI

GLYCEMIC INDEX VALUE

Low GI 0 – 55

Moderate GI 56 – 69

High GI ≥ 70

• The glycemic load (GL) takes into account the amount of

carbohydrate (CHO) in a common serving in addition to

its glycemic index (GI)

– Example: Carrots (peeled, boiled) have a GI of 47

and 5 g CHO per serving

Glycemic Load (GL)?

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GL = (GI of CHO × grams of CHO per serving) ÷ 100

The GL of carrots is: (47 × 5) ÷ 100 = 2.4

GLYCEMIC LOAD VALUE

Low GL 0 – 10

Moderate GL 11 – 19

High GL ≥ 20

GI Determination Protocol

25 g or 50 g CHO of test food

1st hour – Blood taken every 15

minutes

2nd hour – Blood take every 30

minutes

Glucose response value plotted in

graph

Calculate Area Under Curve (AUC)

Test food response compared to

reference food (glucose)

Repeat among 8 to 10 volunteers

GI value

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GI Determination Protocol

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Factors Influencing GI

Type of starch

Physical entrapment

Viscosity of fibre

Sugar content

Fat and protein content

Acid content

Food processing

Cooking 9

[1] Type of starch

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Amylose Absorbs less water

Molecules form tight clumps Slower rate of digestion

LOWER GI

E.g. Kidney beans (28)

Amylopectin Absorbs more water

Molecules are more open Faster rate of digestion

HIGHER GI

Eg. Russet potato (85)

[1] Type of starch

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[2] Physical entrapment

• Bran acts as a physical

barrier that slows down

enzymatic activity on the

internal starch layer.

• Lower GI

– All Bran (38)

– Pumpernickel bread (50)

• Higher GI

– Bagel (72)

– Corn Flakes (92)

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[2] Physical entrapment

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[3] Viscosity of fibre

• Viscous, soluble fibers transform intestinal

contents into gel-like matter that slows down

enzymatic activity on starch.

• High soluble fibre = lower GI

• Lower GI

– Apple (40)

– Rolled oats (51)

• Higher GI

– Whole wheat bread (73)

– Cheerios (74)

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[4] Sugar content

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[4] Sugar content

• Lower GI

– Frosted Flakes (55)

– Raisin Bran (61)

• Higher GI

– Golden Grahams (71)

– Rice Krispies (82) 16

sugar sucrose glucose + fructose

starch maltose glucose + glucose

(GI 60) (GI 100) (GI 19)

(GI 105) (GI 100) (GI 100)

[5] Fat and protein content • Fat and protein slow down gastric emptying, and

thus, slows down digestion of starch.

• High fat and protein foods have lower GI

• Lower GI – Peanut M&M’s (33)

– Potato chips (54)

– Special K (69)

• Higher GI – Jelly beans (78)

– Baked potato (85)

– Corn Flakes (92)

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[6] Acid content

• Acid slows down gastric emptying, and thus,

slows down the digestion of starch.

• Foods with higher acid content = lower GI

• Lower GI

– Sourdough wheat bread (54)

• Higher GI

– Wonder white bread (73)

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[7] Food processing

• Highly processed foods require less digestive

processing.

• Processed foods = higher GI

• Lower GI

– Old fashioned, rolled oats (51)

• Higher GI

– Quick, 1-minute oats (66)

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[8] Cooking

• Cooking swells starch molecules and softens

foods, which speeds up the rate of digestion.

• Overly cooked foods = Higher GI

• Lower GI

– Al dente spaghetti – boiled 10 to 15 minutes (44)

• Higher GI

– Over-cooked spaghetti – boiled 20 minutes (64)

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Low/High GI Meals/ Snacks

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GI = 60 GL = 48 GI = 42 GL = 31


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GI = 85 GL = 48 GI = 39 GL = 22


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GI = 83 GL = 19 GI = 14 GL = 1


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GI = 80 GL = 32 GI = 61 GL = 12


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GI = 57 GL = 31 GI = 32 GL = 16

GI Symbol

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Benefits of Low GI Diet

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Low GI diet helps lower blood glucose levels Meta-analysis of 14 studies, 356 subjects (types 1 & 2 DM), 2-52

weeks duration

Mean difference

• 7.4% in glycated proteins over &

above reduction compared to

high GI diet.

• 0.43% points in HbA1c over &

above reduction compared to

high GI diet

Brand-Miller et al. Diabetes Care. 2003; 26; 2263.


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Low GI diet helps lower blood glucose levels EURODIAB IDDM Complications Study, 1996

2,054 people, 15-60 y, with type 1 DM

Buyken et al. Am J Clin Nutr. 2001; 73; 578.

GI HbA1c

Lowest quartile 58-78 6.04

Highest quartile 86-112 6.60


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Low GI diet improves lipid levels

NHANES III, 1988-1994

13,907 American adults, 20+ y

Ford & Liu. Arch Intern Med. 2001; 161; 572-576.

GI HDL-C

Lowest quintile 52.51

Highest quintile 49.42


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Low GI diet improves lipid levels

23 obese young adults, 18-35 y, BMI > 27, 12 mos. duration

GL Tot.

chol.

LDL HDL TG

Ad libitum low GL diet 53 -8.5 -9.7 12.2 -37.2

Low calorie, low fat diet 77 -6.2 -7.4 1.1 -19.1

Ebbling et al. Am J Clin Nutr. 2005; 81; 981.


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Nurses’ Health Study, 1984-1996

74,091 women, 38-63 y

Lin et al. Am J Clin Nutr. 2003; 78; 923.

Calculated odds ratios (lowest > highest quintiles)

BMI (≥30)

n = 6,400

Major weight gain

(≥25kg) n = 657

Whole grains -19% -23%

Refined grains +18% +26%

Dietary fiber -34% -49%

Low GI diet aids in weight control


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0%

25%

50%

75%

< 18.5 18.5 - 24.9 25.0 - 29.9 30.0 - 34.9 35.0 - 44.9 45.0 +

BMI

% o

f S

ub

ject

s

Burani & Longo. Diabetes Educ. 2006; 32; 83.

Low GI diet aids in weight control Post low GI MNT counseling, 21 subjects, 21-89 y, 3-36 mos.

pre LGI-MNT

post LGI-MNT


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Low GI diet decreases risk of heart disease


75,521 adult women, 38-63 y, free of CHD

10 year follow-up: 761 cases of CHD

Lin et al. Am J Clin Nutr. 2000; 71; 1455-1461.

Relative risk of CHD

GL highest quintile 1.98

GI highest quintile 1.31


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Low GI diet decreases risk of heart disease


78,779 women, 38-63 y, free of CVD

18 year follow-up: 1,020 stroke cases documented

Relative risk

CHO intake (all subjects) 2.05 for hemorrhagic stroke

CHO intake (BMI ≥ 25)

2.13 for total stroke

3.84 for hemorrhagic stroke

GL intake (BMI ≥ 25) 1.61 for total stroke

cereal fiber (all subjects) 0.66 for total stroke

0.51 for hemorrhagic stroke

Oh et al. Am J Epid. 2005; 161; 161-169.


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Low GI diet decreases risk of diabetes.


65,173 US women 40-65 y, free of DM

6 year follow-up: 915 cases of type 2 DM

Relative risk

GI 1.37

GL 1.47

cereal fiber 0.72

GL cereal fiber 2.50

Salmeron et al. JAMA. 1997; 277; 472.

Take home message • Eat high-fiber breakfast cereals (oats, bran, barley)

OR add berries, nuts, flaxseed and cinnamon to high GI cereals.

• Choose dense, whole grain and sourdough breads and crackers OR add a heart-healthy protein and/or condiment to high GI breads and crackers.

• Include 5-9 servings of fruits and vegetables every day.

• Replace white potatoes with yams or sweet potatoes OR consume smaller portion of high GI potatoes.

• Eat less refined sugars and convenience foods (soda, sweets, desserts, etc.) OR combine nuts, fruit, yogurt, ice cream with commercial sweets –watch portion sizes.

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Thank You

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6. glycemic index

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