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Low GI/GL PDF Print E-mail

Not all carbohydrates are digested and absorbed at the same rate. This means that different carbohydrates have different effects on blood glucose (blood sugar) and insulin levels.

The Glycaemic Index [GI] was actually invented in 1981 by Dr Thomas Wolever and Dr David Jenkins at the University of Toronto and is a measure of how quickly a food containing 25 or 50 grams of carbohydrate raises blood-glucose levels. Because some foods typically have a low carbohydrate content, Harvard researchers created the Glycaemic Load [GL], which takes into account the amount of carbohydrates in a given serving of a food and so provides a more useful measure.

The GI gives you an indication of the rate at which carbohydrate-rich foods affect the blood sugar levels after they’ve been eaten. Glucose in this case is assigned a numerical value of 100 and is absorbed almost immediately creating a sharp rise in blood glucose levels (bad). All other carbohydrate foods are compared to this level. The GI represents the total rise in a person's blood sugar level following consumption of the food and is measured on a scale of 0 – 100. The GI is useful for understanding how the body breaks down carbohydrates and only takes into account the available carbohydrate (total carbohydrate minus fibre) in a food.

Glycaemic load (GL) estimates the impact of carbohydrate consumption using the glycaemic index while factoring in the amount of carbohydrate that is consumed. This factors in when you eat the carbohydrate, how much of it you eat and with what you combine it. For instance, watermelon has a high GI (72), but a typical serving of watermelon does not contain much carbohydrate (the bulk being mainly water and fibre), so the glycaemic load of eating it is low (7). However should you eat a quarter watermelon, it will have a more pronounced effect on your blood sugar levels.

Whereas glycaemic index is defined for each type of food, glycaemic load can be calculated for any size serving of a food, an entire meal, or an entire day's meals. For one serving of a food, a GL greater than 20 is considered high, a GL of 11-19 is considered medium, and a GL of 10 or less is considered low. Foods that have a low GL in a typical serving size almost always have a low GI. Foods with an intermediate or high GL in a typical serving size range from a very low to very high GI.

The limitation of LowGI/GL is that it only focuses on carbohydrate-rich foods and does not factor in the effect of protein on the blood sugar level. Although proteins are not classified as carbohydrates, as much as 50% can be converted into glucose depending on how much protein you consume at any given time. Thus you may have carefully calculated the GL level of your meal but you don’t know what effect that rib-eye is going to have on your blood sugar level, followed by the packet of biltong you munch while watching the tennis.

To further complicate matters, certain foods like milk and fish raise blood insulin without affecting blood sugar. This isn’t a concern if your body is balanced and you aren’t insulin resistance. However, if you do suffer with metabolic syndrome, this can wreak havoc with your system especially considering that your satiety hormones are not working so well.

Who should follow the Low GL/GI Diet?

If you can’t live without your ‘daily bread’ or if you still believe in carbo-loading before a game (whilst sitting on the sofa drinking copious amounts of ‘Lite” beer), then best you follow a Low GL diet. At least it might make you think about what is on your plate and how you are combining your food. Just remember that a Low GL way of eating is not necessarily ‘wheat free’, ‘sugar free’, ‘dairy free’, ‘fat free’ or indeed a ‘get out of jail free’ card. This lifestyle is based around carbohydrates and combining it with a high fat diet just because you love cheese and bacon is a recipe for disaterbetes!

 

GI and GL for Common Foods

Food

GI

Serving Size

Net Carbs

GL

Peanuts

14

 4 oz (113g)

15

2

Bean sprouts

25

 1 cup (104g)

4

1

Grapefruit

25

 1/2 large (166g)

11

3

Pizza

30

 2 slices (260g)

42

13

Lowfat yogurt

33

 1 cup (245g)

47

16

Apples

38

 1 medium (138g)

16

6

Spaghetti

42

 1 cup (140g)

38

16

Carrots

47

 1 large (72g)

5

2

Oranges

48

 1 medium (131g)

12

6

Bananas

52

 1 large (136g)

27

14

Potato chips

54

 4 oz (114g)

55

30

Snickers Bar

55

 1 bar (113g)

64

35

Brown rice

55

 1 cup (195g)

42

23

Honey

55

 1 tbsp (21g)

17

9

Oatmeal

58

 1 cup (234g)

21

12

Ice cream

61

 1 cup (72g)

16

10

Macaroni and cheese

64

 1 serving (166g)

47

30

Raisins

64

 1 small box (43g)

32

20

White rice

64

 1 cup (186g)

52

33

Sugar (sucrose)

68

 1 tbsp (12g)

12

8

White bread

70

 1 slice (30g)

14

10

Watermelon

72

 1 cup (154g)

11

8

Popcorn

72

 2 cups (16g)

10

7

Baked potato

85

 1 medium (173g)

33

28

Glucose

100

 (50g)

50

50