Lettuce be straight with each other- THE GI MYTH UNCOVERED

One of the buzz-words in nutrition is the glycemic index (GI). Countless books are written based on the so-called GI. The term is used not only to market processed food, but has become a common catch-phrase in health-consciousness circles. Many people in the sport, diabetic and weight watchers arenas base their entire diet on the GI. But what does this term really mean? Anyone with any nutritional suss should be highly suspicious of the hype.

The glycemic index (GI) is defined as the body’s blood sugar (read glucose) response-ratio to any given food. A refined carbohydrate (such as white sugar) is rapidly digested and absorbed into the bloodstream and will cause an immediate increase in blood sugar levels, whereas a more complex carbohydrate such as a banana for instance, will cause a much slower increase of sugar in the bloodstream.

The concept of GI was first established in 1981 by a certain D. Jenkins and his colleagues as a way to classify carbohydrate-containing foods for the management of glucose in diabetics. GI levels are classified as low (below 55), medium (56–69) or high (higher than 70). To determine the glycemic index of different foods, a specific food is isolated and eaten by individuals and their blood glucose levels are tested after the meal to assess the effect. Any individual’s response to eating white bread or pure glucose is taken as a standard measure for the highest Glycemic Index: i.e. 100.
The problem, however, is that the GI tends to afford the specific foodstuff with a high or low GI label, without taking into account that the index can increase or decrease in relation to the amount consumed. The lowly big pineapple will thus be dispatched to the “bad food” bin with all the other culprits, whereas it is in actual fact totally safe for a diabetic to eat a limited amount.  (Only the truly gastronomically sturdy can eat more than three watermelons for instance – more or less the amount needed to flip the index into danger-zone).

Wouldn’t life be a plum though – if an index existed that would take into account the amounts consumed in order to let the falsely accused “BAD-apples” off the hook? Well it actually does. Instead of lobbing a given food into the out-tray because of one bad performance, the aptly named GL (or Glycemic Load), will consider the fact that a bunch of grapes will have a more dramatic blood sugar response (higher GI), than a single grape. The Glycemic Load is thus the amount of carbohydrate in the food consumed multiplied by the speed of digestion of the said carbohydrate.

This is why, the GI’s lesser known-brother is in fact considered by many experts to be a better measuring tool for sugar levels as it takes into account that both the amount of a certain carbohydrate as well as its rate of digestion and absorption, determine the body’s physiological response to blood glucose input.

Yet, both the GI and the GL seem to be of particular interest to diabetics, weight watchers and sports people, who closely monitor their blood-glucose levels and the effect it has on their systems.

GI and diabetes

The major causes of diabetes type II are:

  • stress in its various forms,
  • the consumption of refined and processed foods – resulting in deficiency of the essential nutrients linked with diabetes such as chromium, vitamin C, magnesium, the B-vitamins, zinc and essential fatty acids,
  • the lack of physical activity, coupled with
  • overweight and obesity.

These factors all contribute to a lowering of the body’s resistance to insulin – the primary cause of diabetes.

It is widely believed that type II diabetes can be prevented by eating foods low on the glycemic index.However, the truth is that high levels of glucose are not what “cause” diabetes – but rather the body’s weak resistance to insulin due to the above mentioned factors. Although foods high on the glycemic index can cause glucose levels to spike, this is just an indicator of the presence of diabetes, not the root cause.

Another common mistake is to assume that the opposite is gospel. But though there is some indication that the lower GI foods may reduce postprandial (after-dinner) hyperglycemia, there is not sufficient evidence of long-term benefits to recommend the use of low GI diets as a primary strategy in food/meal planning for diabetics. There are still substantial inconsistencies in study outcomes.   Research in this field has suffered from flaws in experimental design, small sample sizes, and insufficient short and long-term data.

The fact is that people differ greatly in how well they digest and process specific foods. Thus many people suffering from diabetes have wisely started developing their own “glycemic index” based on their individual experience of blood glucose responses to specific foods and are making insulin-adjustments accordingly.

To effectively prevent and manage diabetes, the focus should rather be on consuming a balanced whole-food diet consisting of mainly unprocessed fruits, vegetables, legumes, seeds, nuts and wholegrains, which supply the body with complex carbohydrates, water-soluble fibre and all the nutrients to maintain proper physiological function. Every meal should be balanced with good sources of plant and/or animal protein. Apart from nutritional status, obesity, inflammation, gut health and toxicity all have a profound effect on a person’s susceptibility to diabetes.

GI in weight loss

Currently, research does not support low-GI eating as a magic bullet for weight loss.  Weight loss observed by those eating a standardised low-GI diet is rather due to more conscious eating, the higher fibre and nutrient content and lower caloric intake that commonly accompanies a low-GI diet – and NOT necessarily due to the low-GI diet-plan itself. Evidence consistently points to the same basic truth: Effective weight loss is a direct result of eating less, being more active, rehydrating the system effectively and consuming a nutrient-dense balanced wholefood diet as described above.

GI and sports

It is generally believed that the GI can be a useful tool to help exercise and fitness-enthusiasts select the right type of carbohydrates to eat before, during and after exercise. However, studies conducted to determine if the GI of carbohydrates affects performance, are not conclusive. The latest trend in the sports arena is to put more emphasis on antioxidants, proteins and beta-glucans than carbohydrates.


With glucose as the yardstick, studies indicate that white bread has a glycemic index of about 70. However, quite strikingly, individual indexes of white bread have ranged from 44 to 132.  In addition, within the same individual, test values have varied by as much as 42%. Although the average value is 70, these results show that using glycemic indexes for individuals are slightly dicey at the very least.

While perhaps a reasonable indicator to predict chronic disease-risk, the carbohydrate classification models based on GI have been a topic of much debate and discourse. Especially in terms of blanket claims about generic energy-effects projected onto individuals. A major constraint of the GI model is the variability of response by individuals to a specific carbohydrate foodstuff. The body’s various responses to food are very complex. People tend to respond and adapt to food nutrients at a rate and level dictated by a cascade of individual physiological differences.

The Institute of Medicine (IOM) stated in its 2002 recommendations that it is difficult to separate other factors that may contribute to blood glucose levels from the effect of the glycemic index. A multitude of factors have an influence on digestion and the absorption of carbohydrates, hence on how carbohydrate foods affect blood glucose levels and thus the GI of a particular food.

These factors include the amount of fibre the food contains, how much is eaten, the amount of fat and protein, and the way it is prepared. Processing and cooking will raise the GI of any food item. The physical form (liquid or solid) and the chemical composition of the starch and fibre will influence the GI value. Studies have shown that blood glucose levels rise less rapidly when eating more slowly. Moreover, food items are seldom eaten in isolation, but rather as part of a balanced meal, in which case the effect of the total meal on physiological function should be considered.

GI levels will also fluctuate according to the geographical source of a food item and between different members of the same food-family. For example, Australian potatoes are reported to have a high GI, whereas potatoes in the United States and Canada have moderate GIs.

When it comes to food and diets generalisation is dangerous. Considering that potatoes, in general, have a high GI – higher even than white refined sugar, standard bread and rice cakes – it would not be desirable in a low GI diet. But from a nutritional point of view, potatoes are far more superior compared to white refined sugar, standard bread and even rice cakes. Furthermore, potatoes have been the staple in many European countries and the way potatoes are consumed there, boiled with its skin on, has a lower GI than the fried, baked, mashed, roasted or microwaved potatoes consumed in countries like the USA. As part of a balanced meal, boiled, less-mature potatoes are a very nutritious wholefood and their consumption should be encouraged, rather than discouraged.

When it comes to processed food, commercial product formulas differ from country to country even though they may have the same brand name.  (Kellogg’s) Special K in Australia is very different to the South African Special K, which has a completely different formulation. The Australian Special K has a GI of 54 and the South African  Special K has a GI of 89. Therefore, IF YOU DO INSIST ON FOLLOWING A STANDADISED LOW GI DIET, AT LEAST make sure that the GI tables that you use reflect the values of the products available in your country.

Seen that either glucose or white bread is used as YARDSTICK against which the glycemic response of each food item is tested, the glucose and bread based indexes OFFER different results and therefore the GI values from these different sources might VARY. MANY authors and researchers mix up the two willy nilly. Even within the confines of the white bread industry itself, different formulas of white bread will offer different results.

Low GI in food processing

Many people believe that foods low in GI is healthy per se. The fact is that even foodstuffs that are high in sugar can have a low GI count. And even Oprah Winfrey knows that sugar is bad for you. The more food gelatises the higher the GI. Sugar competes with starch for the liquid in any given product which prevents gelatinisation. When starch binds with water under heat, gelatinisation takes place, raising the GI. Sugar may thus lower the GI of foods that otherwise would have a very high GI count.

For example, rice crispies have a high GI. When they are sugar coated, the GI is lower and so Coco pops and Strawberry pops have lower GI values than plain rice crispies. Likewise sugar-free Weetbix has a higher GI than the ordinary one with the sugar. Sugar can also lower the GI of baked goods, since it is inclined to bind with the liquid in baking, preventing it from binding with the flour (read starch) and thereby preventing gelatinisation. The GI of the processed product might be lowered, but the detrimental effect of refined sugar on health has not been taken into account.

In other products where the above starch/sugar dynamic does not come into play, manufacturers lower the GI by other means. Sugar is then replaced with so-called bulking agents such as polyols and polydextros and combined with high-intensity synthetic sweeteners like sucralose, aspartame, acesulfame-K and saccharin. Great if you love chemical-draped, synthetic cuisine like curtains marinated in blue nail varnish. Alternatively, they might add fibre supplements like resistant starch (RS).

However, synthetic sweeteners and RS have been linked to cancer.  Although the detrimental effects have been detected mainly in animal-studies, the desirability of increasing levels of RS and synthetic sweeteners in foods, remains questionable.

Nutrients are naturally confined within the fibrous natural plant cell-walls which comprise beneficial soluble (easily dissolvable) and insoluble fibres. Nothing can replace the effects of a natural high-fibre wholefood diet with fruits, vegetables and wholegrains and its merits are certainly not attainable by the addition of ‘fibre supplements’ to fibre-depleted foods. There is enough evidence to suggest that these supplements may even be detrimental to health.

Many white breads are made to achieve a ‘low GI’ by adding fibre supplements or artificial soluble fibre, which has a lowering effect on GI, on a par with insoluble bran-fibre. White bread might thus have the same GI value than wholegrain brown breads, or even lower. However, from a nutritional point of view, wholegrain brown bread should be the favourable choice, not low GI white bread for the simple fact that brown bread is healthier.

The food industry has jumped on the ‘marketing bandwagon’, labelling their products as being ‘low GI’. However, these products are still processed and highly refined, and thus devoid of nutritional value.

Poor indicator of health

The acceptability of a food should not be determined on the basis of a low GI value alone, as many processed and high-fat foods have low GI values while some natural foods with high GI values, such as potatoes and watermelon, are desirable for other reasons.

The general conventional dietary recommendation for health is to consume low fat, low GI foods. This is contradictory, since fat generally lowers the GI of food and a distinction is not being made between healthful unprocessed fats and oils and harmful processed refined fats and oils.

The more acidic a food, the lower the GI of that particular food. For example, beetroot salad with a vinegar dressing will have a lower GI than cooked beetroot without the vinegar. Yet again, from a nutritional and health point of view, beetroot without spirit vinegar would be more desirable.

The perception exists that GI is the best indicator of the amount of carbohydrate (sugar) in a particular food. The GI describes the rate at which glucose is released into the bloodstream; it says nothing about carbohydrate content. The more grams of carbohydrate you consume, the higher the glycemic response, because the glycemic load is greater. If you eat two different foods with a similar GI, the blood glucose response will be greater for the food eaten in greater quantity.  The GI values therefore do not take into account the amount of carbohydrate in a food or meal. Then again, a food with a low content of carbohydrate may nevertheless have a high GI value if that carbohydrate is ingested and absorbed rapidly in the human small intestine. This is potentially confusing for a person wishing to control his or her blood glucose levels by the choice of foods.

There has been much controversy over the application of the glycemic index to the well-balanced meal. This has led to recommendations from the American Diabetes Association that focuses on the total amount of carbohydrates in a meal, rather than the source of the carbohydrate. A low-GI diet does not limit the amount of carbohydrates consumed, but would only attempt to keep food intake at a GI level of 50–55. It also does not take into account the effect of other food in the same meal on blood sugar response, like protein and fat. 


With our mechanistic and reductionistic way of thinking, we overcomplicate matters. Just because you can measure something, doesn’t mean it’s important. For ‘health’ reasons processed foods are being labelled to indicate their carbohydrate, fibre, protein, fat and trans-fat content and now GI. However, they are still processed foods laced with synthetic chemicals like preservatives, colourants and flavourants and devoid of natural soluble-fibre and life-giving bioavailable micronutrients like enzymes, vitamins, minerals and other essential phytochemicals (plant chemicals). Processed food is not health-promoting, low GI or not!

High insulin levels are implicated in all the diseases of our modern lifestyle such as high blood pressure, high cholesterol, high triglycerides, diabetes, hypoglycaemia, ADHD, obesity and coronary heart disease. To prevent these diseases and to maintain physiological health and therefore balanced glucose response, the body needs soluble-fibre and macro- and micronutrients like vitamins, minerals, anti-oxidants, enzymes and many yet to be discovered phytochemicals. This can only be supplied by a balanced unprocessed wholefood diet. Complex carbohydrates (starchy vegetables and wholegrains), rich in soluble-fibre should be balanced with protein and fat in every meal in the ratio of 20% complex carbohydrates, 20% protein and 10% fats and oils. Salad and vegetables should make up the rest of the meal, thus 50%.

For health promotion, the emphasis of any diet should be natural unprocessed wholefoods, eaten in balanced proportions. We should re-think our health education and the proportions portrayed in the food pyramids.

Written by Heidi du Preez



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