Most sportsmen and women and the general public have by now heard of the GI concept. Basically, the GI is a tool for classifying food (not just carbohydrate foods) according to the effect these foods have on blood glucose and insulin levels.
According to the GI concept, foods are divided into the following three categories:
1) Low-GI foods (GI of less than 40)
These foods do not cause a rapid rise in blood glucose or insulin levels, but gradually increase both components in the blood, thus providing a slow, sustained release of glucose and ‘steadier’ blood glucose levels - generally recommended for individuals with insulin resistance, metabolic syndrome, diabetes, overweight and hypoglycaemia.
2) Medium-GI foods (GI between 40 and about 68)
These foods cause an intermediate rise in blood glucose and insulin levels and can be used to increase variety in both the low- and the high-GI diet.
3) High-GI foods (GI of 70 or more)
These foods result in rapid, pronounced rises in blood glucose and insulin levels providing readily available fuel for strenuous activity and are used extensively in sports nutrition to help athletes sustain performance.
The problem with using the GI to classify food is that the public, including sportsmen and women, tend to regard high-GI foods in a negative light. The idea that low-GI foods are “good’ and high-GI foods are “bad” may prevent athletes from using high-GI foods when they really need them to boost their performance or carbo-load.
How to select the correct GI
Selecting foods with the correct GI before, during and after strenuous exercise can be tricky.
a) Before exercise
Research studies where athletes ate low-GI foods about one hour before exercising have not given uniform results. Some studies showed that athletes improved their performance when they ate Durum pasta or lentils (low-GI foods) before exercise, while other studies showed no improvement.
On the other hand, the use of high-GI foods before exercise may cause hypoglycaemia in a small percentage of susceptible individuals and thus have a negative effect on performance.
Based on existing research, the general recommendation is for athletes to eat high-GI food before exercise, provided they also ingest high-GI food and drinks during exercise.
If you are a sportsman or woman and are wondering what to eat one to three hours before an event, then it may be prudent to experiment with both low- and high-GI foods during your training period. Find out if you belong to the relatively small percentage of athletes who develop hypoglycaemia early on in the event if you use high-GI foods in the pre-event period.
If this should be the case, then you need to concentrate on eating low-GI foods (yoghurt, milk, wholewheat Pronutro, high-fibre cereals, muesli containing nuts and dried fruit, Provita, seedbread, lentils, baked beans, soya, cooked and cooled samp, pasta made from 100% Durum wheat, cooked and cooled maize meal porridge, parboiled white rice, wild and brown rice, tinned corn, deciduous fruit (apples, plums, pears), vegetables, energy drinks, milo, Ensure, mageu) before exercise.
If you find that some of these foods cause gastric distress during the event, avoid them and rather use low-GI foods that agree with your digestion, for example some athletes may develop cramps and winds if they eat seedbread but not when they eat muesli, so the latter food would be a better pre-event choice.
If you are not prone to hypoglycaemia, then you can ingest medium- or high-GI foods and drinks in the period before exercising. Sports drinks and energy bars that contain glucose, maltose, sucrose, maltodextrins and/or amylopectin provide a mixture of medium- and high-GIs.
b) During exercise
Research has repeatedly shown that using high-GI food and drinks during strenuous exercise enhances performance, prevents exhaustion, increases blood sugar levels, which act as a source of readily available energy, and decreases the risk of upper respiratory tract infections.
All athletes who exercise intensively and/or for long periods can benefit from using high-GI foods and drinks during an event.
Because it is often difficult to use standard foods during strenuous exercise (e.g. most runners can’t eat a bowl of breakfast cereal during a marathon!), serious athletes will probably find that they need to use sports drinks (Game, Energade, Powerade, Lucozade) and energy bars while participating.
Once again, it is important to test the different products available on the market to see how you react. Do your experimenting during your practice sessions and avoid those products that cause gastric distress.
c) After exercise
The recovery period is an essential part of an athlete’s diet and, if neglected, can lead to poor performance in the long term. Most researchers agree that high performance athletes need to ingest 7-10 g of high-GI carbohydrates in the first 24 hours after a strenuous event. The high-GI carbohydrates ensure that glycogen stores in the liver and muscles are replenished.
A study conducted by Burke and coworkers (1996) showed that there was little difference in glycogen storage when the high-GI foods were eaten as 16 snacks or four meals during the 24 hours after an event. You can decide what regimen is easiest for you to follow during the post-exercise period: plenty of small high-GI meals or snacks, or four larger high-GI meals.
The following are classified as high-GI foods and drinks:
Wheet Bix, instant oats, oats raw and cooked, maize meal (all varieties eaten hot with or without sugar), puffed wheat, Rice Crispies, Coco Pops, Cornflakes, Fruit Loops, Special K, white sticky rice, potatoes, pasta made from standard wheat, cooked samp, all white, brown or wholewheat bread, rolls, bagels, buns, Melba toast, plain scones and muffins, cream crackers, rice cakes, snackbread, spanspek, watermelon, litchi juice and medley of fruit juices, carrots, pumpkin, butternut, turnips and parsnips, sweets (boiled, jelly-type, marshmallows, toffees), corn chips, strawberry energy bars, tapioca made with milk, biscuits (wafers, Marie, Boudoir), honey, syrup, glucose, sugar-free jelly made with maltodextrin, tofu, all energy sports drinks.
Athletes need high-GI foods
It is therefore evident that high-GI foods are an important part of the diet of sportsmen and women who train and exercise strenuously for many hours a day.
Each athlete needs to determine which of these foods listed above give the best results (no gastric discomfort and enhanced performance, less fatigue, rapid recovery, fewer respiratory tract infections and overall well-being). Start experimenting long before that Big Event.
If you are uncertain where to start or how to set about planning your carbohydrate and GI intake, consult a clinical dietician to help you obtain the maximum benefit from carbohydrates and the GI. – (Dr I.V. van Heerden, DietDoc)
Any questions? Ask DietDoc