Updated 06 February 2017

The glycaemic index and diabetes

One of the most important applications of the glycaemic index is its use in the control of blood sugar and insulin levels in diabetes, insulin resistance and metabolic syndrome.


In addition, low-GI foods can help to control blood sugar levels in hypoglycaemia and assist with weight loss in obese people.

Basic principles
When human beings eat food, the food is digested in the gastrointestinal tract and absorbed into the blood stream. Carbohydrates are broken down into glucose, a simple sugar that causes the blood glucose level to rise. In response to such an increase in blood sugar levels, the pancreas produces a hormone called insulin, which is supposed to transport the glucose out of the blood, across cell membranes and into the cells of the body where it can be used as fuel.

If a person has problems with insulin production, glucose is either not cleared from the blood and the blood glucose levels remain high, as in diabetes. If too much insulin is produced, the blood sugar levels fall too quickly and too far, as in hypoglycaemia.

The following insulin production problems can occur:

  • The pancreas is not able to make sufficient insulin - this results in so-called type I, or insulin-dependent diabetes mellitus, where patients have to use insulin injections to control their blood sugar levels.
  • The pancreas does produce insulin, but the amount is either insufficient, or the insulin is ineffective - this is characteristic of type II, or non-insulin-dependent diabetes, insulin resistance and the metabolic syndrome.
  • The pancreas produces too much insulin as in hypoglycaemia.

The GI and insulin control
Researchers have found that eating foods with a low GI can prevent undesirable variations in blood insulin levels. It is, therefore, not surprising that the GI of foods can be used to treat the various conditions that are linked to problems with insulin production, namely both types of diabetes, hypoglycaemia, insulin resistance and the metabolic syndrome.

One would thus expect that patients with any of the above-mentioned conditions would be told to eat only food with a low GI. But, such a recommendation is not really feasible or practically possible.

The following guidelines should be kept in mind by anyone who has problems with insulin production and blood glucose levels:

  • Food with a high GI, such as cooked maize meal or different types of bread (white, brown and wholewheat), can still be included in the diet but they need to be combined with low-GI foods, such as fat-free cottage cheese or yoghurt, and spaced through the day - eat one high-GI food at each meal instead of all at one meal (e.g. instead of eating maize meal porridge and two slices of wholewheat toast at breakfast (three high-GI foods in one meal), it is better to have the maize meal porridge at breakfast and one slice of wholewheat bread at lunch and at supper (three high-GI foods spread over three meals).
  • When selecting fruit, remember that stone fruit (plums, peaches), apples, pears, citrus, berries and kiwi fruit have a low GI, while tropical fruits such as pawpaw and melons have a high GI - once again, high-GI fruits need to be spread over the day, not all eaten at one meal.
  • Sugar surprisingly has a moderate GI of 68 and 30 g, or three tablespoons, of sugar a day can be included in the diets of individuals with diabetes and insulin resistance - this does not give you carte blanche to eat sugar in uncontrolled quantities, but it does permit its use in small quantities to make food more palatable.
  • Even if you eat low-GI foods, this does not mean that you can eat uncontrolled quantities of these foods and not expect to gain weight - portion sizes remain one of the best guidelines for controlling undesirable variations in blood insulin and glucose levels.
  • A desirable goal is to replace 50 percent of the carbohydrates in your diet with low-GI choices, which means you can still include some high-GI foods so as to add variety to the diet.
  • Also try to include at least two low-GI foods on a daily basis.

The most important recommendation
Perhaps the most important thing anyone with insulin problems can do is to consult a clinical dietician. There is probably no other type of condition where dietary guidance is more crucial to the patient's health than in derangements of insulin metabolism.

If you suffer from diabetes, insulin resistance, metabolic syndrome, or hypoglycaemia, you should contact a dietician. You need someone to work out an individual diet for you, which will also help you to understand and use the GI correctly.

If you have been diagnosed with diabetes, insulin resistance or hypoglycaemia, ask your doctor or clinic to refer you, or look up your nearest dietician in the Yellow Pages or contact the Association for Dietetics in SA at (011) 447-4157. You won’t regret it. – (Dr I.V. van Heerden, DietDoc, February 2007)


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Dr. May currently works as a fulltime endocrinologist and has been in private practice since 2004. He has a variety of interests, predominantly obesity and diabetes, but also sees patients with osteoporosis, thyroid disorders, men's health disorders, pituitary and adrenal disorders, polycystic ovaries, and disorders of growth. He is a leading member of several obesity and diabetes societies and runs a trial centre for new drugs.

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