Glyemic Index and Glycemic load
Glycemic load is a way of determining how much glucose enters the bloodstream when a particular food is eaten.
All carbohydrates are converted to glucose – yes rice, pasta, apples and onions. Once eaten they break down into glucose in the gut. The glycemic load is calculated by multiplying the glycemic index of a carbohydrate by the actual amount of glucose in the portion size eaten (carbohydrate density). The resulting answer shows you how much actual glucose enters the bloodstream after a particular meal.
All carbohydrates when digested are broken down into glucose. Single glucose molecules are able to get absorbed from the gut into the bloodstream. Carbohydrates break down into single glucose molecules at different speeds during digestion. If a carbohydrate breaks down very quickly, you get relatively more glucose crossing from the gut into the bloodstream in a short space of time, increasing blood sugar levels rapidly. Your body responds to rapidly rising blood sugar with a large release of insulin.
The glycemic index (GI) is a measurement of how quickly each carbohydrate reaches the bloodstream as pure glucose. The glycemic index is measured by consuming a food containing 50g of available carbohydrate, and then measuring blood glucose each 15 – 30 minutes for 2 – 3 hours. The results are mapped onto a graph. A curve is then compared to a reference food – usually glucose. The lower the GI of a food, the flatter the curve on the graph, the slower it is digested and converted to glucose. Glycemic index ranges is referenced against glucose, which has the value of 100.
High glycemic index = greater than 70
Intermediate glycemic index = 55 – 70
Low glycemic index = less than 55
Many of the foods we eat in abundance today are high in Glycemic index – most breads, grains, crackers, muffins and cakes are high GI. So we are constantly eating foods that push our blood sugar levels up high.
In general the more food is processed the the faster it will break down. E.g. fine ground flour in white bread, instant potatoes. Food that is less processed and contains more fibre and is in a larger piece so it will break down more slowly e.g. whole vegetables.
Here are some examples of the different densities of carbohydrates, that is the amount of glucose that the food is converted into.
1 cup of cooked rice, polenta, couscous = 10 teaspoons sugar (3 ½ tablespoons) i.e 45 grams
1 cup cooked pasta = 8 teaspoons sugar, 40g
1 baked potato = 8 teaspoons sugar, 40g
1 cup broccoli = ½ teaspoons sugar, 3g
1 cup pineapple = 4 teaspoons sugar, 18g
1 cup strawberries = 2 teaspoons sugar, 9g
As you can see the paleo foods (fibrous fruit and vegetables) have a far lower density, so they do not turn into loads of glucose.
Many of today’s everyday foods are high in density and are also high in glycemic index, and when eaten in a typical portion, we get a large amount of sugar going into our bloodstream very quickly, in other words a large sugar load, called Glycemic load.
When we take some typical foods and work out glycemic load – you can see there is a big difference between grains and paleo foods. Paleo carbohydrates – vegetables and fruit are typically low in glycemic load.
Glycemic load = GI x carbohydrate grams per serving, then divide by 100
Here are some examples:
Pasta (GI) 37 x 42grams (1 cup) = 16
Bagel (GI) 72 x 35grams (1 whole) = 25
Apple (GI) 36 x 18grams (1 whole) = 6.5
Broccoli (GI) 5 x 10grams (4 cups cooked) = 0.5
More on the Glycemic Index can be found here, from the University of Sydney
Here is an overview of a number of foods and their glycemic index (all foods, not paleo only)
To work out the Glycemic load, multiply a typical serving size by the GI number as shown above, then divide by 100
Glycemic index of foods
Glucose is the reference food, GI glucose is 100
Low GI foods are those below 50, Moderate GI foods are between 50 – 70 and high GI are more than 70.
Breads & Crackers
French Baguette 95
Rice cake 82
Rice cracker 82
Water cracker 78
Wholemeal bread 71
White bread 70
Pita bread white 57
Vita wheat 55
Sourdough wheat 54
Burgen Soy Lin 36
Rice bubbles 89
Coco pops 77
Just right 60
Muesli untoasted 56
Special K 54
Sultana Bran 52
Porridge (ave) 50
Muesli toasted 43
All bran 30
Grains / pasta
Calrose rice 83
Basmati rice 59
Brown rice 55
Long grain white rice 50
Pearled barley, boiled 25
Bulgur wheat 48
Noodles, instant 47
Egg fettuccine 32
Dates, dried 103
Rock melon 65
Potato, baked 85
French Fries 75
Potato, new 62
Kidney beans, canned 52
Baked beans 48
Chick peas 33
Black beans 30
Kidney beans 27
Soya beans 18
Dairy foods Note – dairy products trigger a much bigger insulin response than the glycemic index would indicate.
Milk, skim 32
Milk, whole 27
Yoghurt, flav, low fat 33
Ice-cream 36 – 80 (hte more fat the low the GI)
Soft drinks 68
Orange juice 53
Apple juice 41
Tomato juice 38
Jelly beans 80
Life savers 70
Mars bar 68
Muesli bar 61
Fructose 20 (Although low GI fructose has other problems as it needs to be processed by the liver)