Eating with the GI

Do you permanently have the munchies? Do you often lack energy? Are you a diabetic or an athlete? Then the term glycaemic index(GI) is worth remembering.

It may sound like a mouthful, but the concept is actually quite simple to grasp: GI refers to the effect of carbohydrate foods on blood sugar (glucose) levels. Foods with a high GI release energy in the form of glucose quickly (to which the body reacts with insulin), foods with a low GI ensure a slow release of glucose (requiring less of an insulin response), and foods with an intermediate GI are somewhere in between.

For stabilising blood-sugar levels – for example, if you lack energy or are trying to lose weight – a diet rich in low-GI foods is recommended. And if you're diabetic or insulin-resistant, such a diet is ideal. In fact, scientists now know that concentrating on low-GI foods makes a lot more sense in terms of diabetes management than trying to cut out sugar.

High-GI foods can also be useful, especially if you're an athlete. While you should focus on eating low-GI foods in the days preceding an event, high-GI foods eaten immediately before the event will give you a spurt of energy (endurance-event athletes should, however, focus more on eating low-GI foods). Straight after the event, high-GI foods can also help to replenish energy stores.

On a scale of 0 to 100, carbohydrate foods are given a GI value. At the top of the scale, i.e. 100, lies pure glucose. The glucose-releasing effect of all other foods is compared to this value. High-GI foods have values of 71 – 100, intermediate-GI foods have values of 55 – 70, and low-GI foods have values of less than 55. The lower the value, the lower the GI, and vice versa.

Factors that influence GI
Several factors influence a food's GI. These include:
- The type of carbohydrate the food contains – e.g. intact grains such as wheat or maize have much lower GI values than flours made from the same grains and long-grain rice and legumes  are more difficult to digest than wheat flour.
- How it has been processed or cooked – cooking and processing change the structure of food, which may delay or increase absorption by the body.
- The temperature of the food – when some cooked starches cool down, a more resistant starch develops, causing a GI-lowering effect.
- The presence of fat and protein – a mixed meal containing small amounts of fat and protein tends to have a lower GI, as both fat and protein slow down the digestion of carbohydrates.
- The presence of dietary fibre – foods containing soluble fibre, such as rolled oats and legumes, have a lower GI, because fibre delays the digestive process.
- The acidity of the food – acidity delays the emptying of the stomach and thereby lowers the GI of a food.
Practical tips
It can be difficult to determine whether a food has a high, intermediate or low GI value just by looking at it. For example, certain fruits have a high GI (e.g. pineapple and apricots), while others have a low GI (e.g. grapefruit and plums), so the type of food doesn't really give you an indication of its GI.

However, over the past few years, experts from all over the world have determined the GI values of specific foods through scientific processes. Your best bet is to consult a reputable online source for a list of GI values of common foods.

But instead of trying to remember which foods are low GI and which aren't, it might be simpler for you to try to reduce (or increase) the GI of your meals.

As the GI is most useful in the diets of diabetics, slimmers and those who lack energy, here are a few practical tips on lowering the GI of your meals:

- Add oat bran to breakfast cereal, fruit and yoghurt, or muffin recipes.
- Combine carbohydrate foods with protein and/or a healthy fat, e.g. eat tuna or scrambled egg with a slice of toast, spread with a thin layer of soft margarine.
- If you have a choice, always go for fibre-rich foods, e.g. whole-grain pasta instead of white pasta.
- Choose low-GI breads instead of regular brown or white bread – it's a little bit more expensive, but will keep you fuller for longer.
- Add vegetables to a starchy meal, e.g. eat a green salad with meat and rice to lower the high GI of the rice.
- Add an organic acid such as Balsamic vinegar to a high-starch meal, e.g. eat Greek salad with a bit of oil and vinegar.
- Add legumes to meals, e.g. add chickpeas to a tomato stew or have three-bean salad when you're eating a sandwich at lunch-time.
- Eat cold potato salad instead of hot boiled potatoes (just go easy on the mayonnaise!) – the GI of potatoes is lowered when it has been cooled.
Sources:
- Nutrition for Life, by Lisa Hark & Dr Darwin Deen, published by Dorling Kindersley Ltd (2006).
- The South African Food Advisory Consumer Service (www.foodfacts.org.za)