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Thursday, 3 July 2014

The Glycemic Index

Sugars: are they all the same?

Sugar, an essential source of fuel for the human body, is consumed and assimilated in many different forms. From a nutritional point of view, sugar belongs to the carbohydrate family, which can be divided into:
  • polysaccharides or complex sugars such as bread, pasta, potatoes and rice;
  • disaccharides such as sucrose (common table sugar) and maltose;
  • monosaccharides such as glucose and fructose.
Gli zuccheri: tutti uguali?
Between them, the three categories are diverse from both a chemical and nutritional point of view. Our diet must include all three, but often tends to be richest in those which are least beneficial to our health. So how do you distinguish foods containing 'good' sugar, which are suitable to eat, from 'bad' sugar, which should be avoided? This is where the Glycemic Index (GI) comes in.

The system ranks foods rich in carbohydrates based on their effect on the glycemia, in other words their ability to raise or lower blood sugar levels following consumption. For example, a low glycemic index of around 50 represents carbohydrates which are absorbed slowly, releasing glucose gradually into the blood stream, whilst a high glycemic index of around 100 or higher indicatesrapid absorption, and therefore high glycemic 'spikes'.

A sudden spike in glycemia stimulates the release of a hormone called insulin, which reduces blood glucose levels by forcing it to be stored in cells. Blood glucose levels may subsequently fall too low, thereby transmitting a message requesting more sugars and stimulating the desire to eat.

A carbohydrate-rich diet with a high glycemic index may therefore give rise to a damaging physiological mechanism which often leads to dietary disorders related to overweight andobesity.

It follows that high GI foods should be consumed in limited quantities. This group particularly includes sugary drinks (soft drinks such as cola, orange squash and citrus drinks), sweets,biscuitspotatoeswhite bread and rice.
Meanwhile there are other foods which also provide carbohydrates, but which are not rapidly assimilated, therefore they do not cause an abnormal rise in glycemia or insulin levels in the blood stream.
This category of foods includes the majority of vegetables (with the exception of potatoes, pumpkin, beetroot and carrots) and fruit (except bananas, persimmons, certain types of exotic fruit and certain types of dry fruit, such as raisins and figs).
It is therefore advisable to consume foods with a low glycemic index which help maintain the most stable blood sugar level, thereby guaranteeing better control over hunger.
The Glycemic Index of some common foods
G.I. values
20 - 38
Whole milk
23 - 31
24 - 53
28 - 44
31 - 51
Natural yoghurt
32 - 40
36 - 40
Orange juice
46 - 54
46 - 59
Kiwi fruit
47 - 59
Wholemeal bread
50 - 56
31 - 63
39 - 75
32 - 95
Rye bread
50 - 64
51 - 63
57 - 64
Dry biscuits
61 - 67
Cane sugar
63 - 73
Orange squash
62 - 74
65 - 75
Chips (frozen)
approx. 75
White bread
30 - 110
White rice
48 - 112
52 - 98
55 - 89
Boiled potatoes
56 - 101
Roast potatoes
77 - 101
Corn flakes
approx. 91
Note: the Glycemic Index in the table is compared to glucose (GI value of 100). 
Data source: International table of glycemic index and glycemic load values (Foster-Powell K, Holt SH, Bran

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