The glycemic index (GI) is a ranking of foods on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Some foods on the Australian market already show their GI rating on the nutrition information panel and very little products in the NZ market utilise the Certified Gi Symbol.
Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health.
Case Studies
Many studies and most recently from Harvard School of Public Health indicate that the risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the GI of the overall diet. The World Health Organisation (WHO) and Food and Agriculture Organisation (FAO) recently recommended that people in industrialised countries should base their diets on low-GI foods in order to prevent the most common diseases, such as coronary heart disease, diabetes and obesity.
The Future of Gi Eating
The GI of foods has important implications for the food industry. Terms such as complex carbohydrates and sugars, which commonly appear on food labels, are now recognised as having little nutritional or physiological significance. The WHO/FAO recommend that these terms be removed and replaced with the total carbohydrate content of the food and its GI value. However, the GI rating of a food must be tested physiologically and only a few nutrition research groups around the world currently provide a legitimate testing service.
Testing GI Foods
The Human Nutrition Unit at the University of Sydney has been at the forefront of glycemic index research for over a decade and has tested dozens of foods as an integral part of its program. Jennie Brand Miller (JBM) is the senior author of International Tables of Glycemic Index published by the American Journal of Clinical Nutrition.
JBM's books, The GI Factor and related pocket books on diabetes, heart disease and weight reduction are aimed at lay people and health professionals, and have sold more than 500,000 copies.
All versions include back-of-book tables of the GI values of some 350 different foods in Australia and NZ, many of them tested in the Human Nutrition Unit. Popular health books and articles in women's magazines by other authors on topics as diverse as breast cancer and weight loss have also included GI tables. These publications have generated an increasing demand for GI testing.
In the near future, many more foods are likely to carry the GI on their nutrition panel. The services of a professional GI testing service such as SUGiRS will therefore allow food companies to take advantage of GI marketing opportunities.
The NZ and Australian Institute for Low GI Foods have successfully added the Low GI symbol (see above) to the Certified Food Programs such as USANA NZ Reset 5 day Program. Which not only has the Low GI Symbol, but was the first Certified Low GI Complete Meal System available in NZ and Australia.
Gi Foundation Here you will find information on the Glycemic Index of foods, latest GI data, new research, GI books, GI testing services and information on the GI symbol program.
What is Glycemic Index of Food?
The glycemic index of food is a ranking of foods based on their immediate effect on blood glucose (blood sugar) levels.Carbohydrate foods that breakdown quickly during digestion have the highest glycemic indexes. Their blood sugar response is fast and high.Carbohydrates that breakdown slowly, releasing glucose gradually into the blood stream, have low glycemic indexes.
What is the significance of Glycemic Index?
Low GI means a smaller rise in blood sugar and can help control established diabetes
Low GI diets can help people lose weight and lower blood lipids
Low GI diets can improve the body's sensitivity to insulin
High GI foods can help re-fuel carbohydrate stores after exercise
How to switch to a low GI diet
Certified Low Gi Breakfast cereals based on wheat bran, barley and oats
"Grainy" breads made with whole seeds
Certified Low Gi Breads
Wholegrain Pasta and brown rice
Kumara in place of potatoes
Vinegar and lemon juice dressings
As mentioned in Nutrition for the endurance athlete, a high carbohydrate diet is a must for optimum sports performance because it produces the biggest stores of muscle glycogen (the storage form of glucose).
Any good book on nutrition for sports will also tell you "carbo-loading" in the days prior to the competition is very important to enhance performance.
The carbohydrate we eat is stored in the body in the form of glycogen in the muscles and liver. A small amount of carbohydrate circulates in the blood as glucose.
When you are exercising at a high intensity, your muscles rely on glycogen and glucose for fuel. Although the body can use fat when exercising at lower intensities, fat cannot provide the fuel fast enough when you are working very hard.
The bigger your stores of glycogen and glucose, the longer you can go before fatigue sets in. Unlike the fat stores in the body, the carbohydrate stores are small. They are fully depleted after two to three hours of strenuous exercise. This drying up of carbohydrate stores is often called "hitting the wall". At this stage, the blood glucose concentration begins to decline at this point, which may lead to symptoms such as confusion and even unconsciousness.
The glycaemic index (GI) factor is now used to describe differences between carbohydrate foods, based on their rate of digestion and physiological effect on blood sugar levels. It was thought that our bodies absorbed and digested all simple sugars quickly, producing rapid increases in our blood sugar levels, but this assumption was simply not correct.
USANA NZ and USANA Health Sciences 'Ask The Scientists' explain this very well in How To calculate your Gi Load
Carbohydrates are now classified according to their blood glucose response or "glycaemic index", which is a ranking of foods based on their ability to increase blood glucose levels. The glycaemic index measures how fast the carb of a particular food is converted to glucose and enters the bloodstream. The lower the number, the slower the action and the better it is for the sports person. The rate at which glucose enters the bloodstream affects the insulin response to that food and ultimately affects the fuels available to the exercising muscles.
We now even have tables listing the carbohydrate-rich foods that promote a high glucose response (called high glycaemic-index foods or high GI) and those that produce lower responses (low GI). There are times when low GI foods provide an advantage and times when high GI foods are better.
For best performance, a serious athlete needs to learn which foods have high and low GI factors and when to eat them.
Bread, cornflakes, rice crispies and other low-fibre cereals are digested and absorbed extremely quickly. For example, white bread has a high GI factor of around 75 and many breakfast cereals have GI factors between 80 and 90. These figures are nearly as high as pure glucose, which has a GI factor of 100. This means that the digestion of such starchy food is almost instantaneous and the blood sugar rise is consequently very rapid.
Fortunately, there are still some foods in our diet that remain slowly digested and absorbed. These foods have a GI factor of less than 50. They included all kinds like pasta, barley, wholegrain, high-fibre cereals and some varieties of rice and bread. They also include many foods made with lentils, chickpeas, couscous and barley.
It is important to appreciate the type of event where looking at the GI factor will help. It is one in which the athlete is undertaking a very strenuous form of exercise for longer than 90 minutes, during events like running, a marathon or a triathlon.
Before an Event
Low GI foods are best before an event - approximately two hours before the big race, allowing time for the food to leave the stomach and reach the small intestine. Nausea and stomach cramps can be experienced if you eat too close to the race, e.g. less than an hour beforehand.
The slow rate of carbohydrate digestion in low GI foods helps ensure that a steady stream of glucose is released into the bloodstream during the event. The extra glucose is then available when needed towards the end of the exercise, when muscle carbohydrate stores are running low. High GI foods like potatoes will produce a rapid increase in glucose and insulin levels, something which is not desirable just before a race when glycogen stores should already be fully charged. Some low GI foods such as legumes are high in fibre and may cause gastrointestinal discomfort.
However, not all low GI foods have a high fibre content - rice and white pasta are good examples of low GI foods that don't contain much fibre.
High Fibre Protein Drink Is a Great Low GI Healthy Breakfast Option
If you're wanting a High Fibre Protein Shake you can purchase
USANA Nutrimeal which has a very generous 8 grams of Fibre per shake - most people add in USANA Fibergy, a specific Fibre product, each tablespoon (tb) places an additional 12g of Fibre.
Aim to have 30g Fibre + per day.
1 USANA Nutrimeal Shake and 1tb USANA Fibergy = 20g Fibre plus 17g high quality protein and essential vitamins/minerals and essential fatty acids. The Perfect breakfast Meal. Certified Low GI as well.
Sports Drinks?
Most of the sports drinks that athletes currently drink have not been tested for their GI factor. Theoretically, the mixtures of sugars present would give a high GI of about 70. So they may not be an advantage before an event, but they are a valuable aid during the event when blood sugar needs to be topped up, as well as after the event when glycogen stores need to be replenished. You should experiment during training sessions to determine timing and amount of low GI food that you should be eating. Don't try out any new routines for the first time on the day of the competition.
During an event
During a competition, many athletes supplement their carbohydrate stores by consuming sugars in one form or another - sports drinks, bananas, etc. These foods provide extra glucose for the exercising muscles when they need it most. It is a well-known fact that carbohydrate consumption during strenuous exercise extends endurance for a lot longer than otherwise possible. High GI foods should be used during long-lasting events. This form of carbohydrate is rapidly released into the bloodstream.
Liquid foods are usually tolerated better than solid foods while racing because they are emptied more quickly from the stomach. Sports drinks are ideal during the race because they replace water and electrolytes as well. Jelly beans are also a good option during a race.
After an event
It is important to replenish glycogen stores in the muscle as soon as possible after the race. And this is where high GI foods can help, since they are digested and absorbed much faster and stimulate the hormone insulin, the hormone responsible for getting glucose into the muscle in the form of glycogen. Good examples include sports drinks (which replace water and electrolytes losses, too), some forms of rice, potatoes, bread, breakfast cereals with a high GI such as cornflakes and rice crispies.
See what is practical for you - the primary goal is to make sure you eat and drink carbohydrate soon after the exercise session.
If you want to keep up the pace, you will benefit by learning to use the GI in selecting foods at appropriate times. The GI can be the means to improved sports performance and swifter recovery.
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Dale Folland
Nutritionist
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