The glycemic index (GI) of a carrot is 92. The GI of a chocolate bar is 68. Does this mean we should substitute chocolate for carrots at our meals to lower our blood glucose levels? The message from the GI can be confusing. Let's break it down into some practical tips for everyday use.
The GI is simply the measure of change in blood glucose levels after a food is eaten. A number from 0 to 100 is assigned to each food based on how much and how quickly it is converted to glucose in the body.
Foods with a high GI are digested and absorbed quickly, leading to spikes in blood sugar levels. Low-GI foods, by contrast, are digested slowly, causing blood sugar to rise more gradually. It was developed in the early 1980s and much research has followed that has boosted its popularity.
The idea behind the GI is that foods with a lower GI result in lower postprandial (after meal) blood glucose values. Well, this is only partly true. The biggest problem with the GI is that it measures only the type of carbohydrate, not the amount in a usual serving size.
For example, the GI for carrots was developed using seven whole carrots - and they weren't baby carrots! For most people, seven carrots is not a typical serving size. I wonder if it's even a typical serving for most rabbits!
Another source of much confusion is that the GI of the same food can vary. As fruit ripens, it becomes sweeter, so its GI increases along with its sugar content. For example, the GI of an under-ripe banana is 42 and the GI of an over-ripe banana is 64. Cooking time can also change a food's GI - a longer cooking time increases the GI and cooling the same food decreases it -so cooked cold potatoes have a lower GI than cooked hot potatoes!
Other factors that change a food's GI include whether grains are processed, the soil content of the state or county where the food was grown, or what other ingredients have been added to it. For example, more fat will lower an item's GI because fat slows the digestion of carbohydrate, which is why a chocolate bar has a lower GI than a carrot.
With all of this variation in GI, is there a good way to use this system to help you make good food choices? Start by choosing low- and medium-GI foods to replace high-GI foods in your diet. To do this you will need to look at the GI Table. Instead of just numbers, it categorizes foods into low (<55), medium (56-70), and high (71-100) GI foods.
The GI isn't a panacea for lowering your postprandial blood glucose levels, but it may help you fine-tune your meals. Try preparing meals without high-GI foods, see what happens to your glycemic control, and let me know what you do or don't like about the GI.
