Understanding Glycemic Index

Many of the terms we come across in articles or advice on healthy eating or developing a balanced diet seem deliberately designed to baffle and bamboozle us. ‘Glycemic index’ is a case in point. You’ll often hear it mentioned in the context of blood sugar, but it is not immediately obvious what it relates to, or more importantly, how we can effectively use the information to help us on a day-to-day basis.

‘Glycemic’ is a word derived from two Greek words for ‘sweet’ and ‘blood’: the glycemic index – or GI as most people refer to it as – is a system of rating and ranking different foods to indicate how quickly the carbohydrates they contain are broken down into blood sugar.

The carbohydrates in foods which have low GI ratings will be absorbed more slowly into our blood sugar. Those with high GI ratings, not surprisingly, are absorbed much more quickly.

Why is this rating system useful? Well, the primary purpose of eating food is to provide our bodies with energy. The longer-lasting that supply of energy, the less likely we are to get cravings between meals, to graze or binge. So foods with lower GIs trickle glucose or sugar into our system, while those with higher GIs tend to give a quick hit of sugar which can lead to a series of peaks and troughs, dips and swings.

You’ve probably met someone who says that their blood sugar level is dropping and they need some sugar intake. That’s an indication that they are probably having rather too many high GI foods. Ideally we should be aiming to balance the mix of high and low GI foods to flatten out those peaks and troughs. Anyone who suffers with diabetes will be all too familiar with the importance of balancing out blood sugar levels.

In general, high GI foods include – perhaps obviously – sugar and sugary soft drinks, as well as rice, white bread and potatoes. The lower end of the scale includes wholegrain foods (wholegrain not wholemeal), pulses like lentils, porridge and muesli. GI levels are also affected by methods of cooking: baking potatoes with their skins on leads to a lower GI rating than boiled potatoes.

It is tempting to assume that foods with high GI ratings are unhealthy and vice versa. That is not necessarily the case. Good examples are that chocolate cake has a lower GI index than watermelon, and crisps cooked in fat are lower than potatoes not cooked in fat. So the fact that those crisps have a lower GI index does not mean you should start basing your diet around them!

Also, the rating is based on comparing the impact on the blood sugar levels of 50g of carbohydrate in whichever food is being tested, compared to 50g of glucose. It is highly unlikely you will ever be eating precisely 50g of carbohydrate in one serving of a particular food, so these GI ratings can only ever be a guideline.

GI is just one factor to take into account when you are thinking about your overall diet; eating nothing but low GI foods would tend to lead to an increase in weight gain. Gradually try changing to a few lower GI foods (rye or granary bread, say, or whole wheat pasta or noodles) and see if you notice an overall improvement in your energy levels – and a little less snacking…

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