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.

 

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 higherindicates rapid 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,biscuits, potatoes, white 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.

Study conducted by the Technogym Studies and Research Centre

The Glycemic Index of some common foods

Food G.I. values
Beans 20 - 38
Whole milk 23 - 31
Plums 24 - 53
Apple 28 - 44
Orange 31 - 51
Natural yoghurt 32 - 40
Pear 36 - 40
Orange juice 46 - 54
Grapes 46 - 59
Kiwi fruit 47 - 59
Wholemeal bread 50 - 56
Carrots 31 - 63
Muesli 39 - 75
Honey 32 - 95
Rye bread 50 - 64
Spaghetti 51 - 63
Apricots 57 - 64
Dry biscuits 61 - 67
Cane sugar 63 - 73
Orange squash 62 - 74
Bananas 65 - 75
Chips (frozen) approx. 75
White bread 30 - 110
White rice 48 - 112
Crackers 52 - 98
Popcorn 55 - 89
Boiled potatoes 56 - 101
Roast potatoes 77 - 101
Corn flakes approx. 91
Glucose 100

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