The concept of ‘Glycemic Index’ was first proposed by Prof. David Jenkins of University of Toronto in 1981. Glycemic index (GI) of a food refers to the property of the food to increase the blood glucose level and is a measure of the ‘quality’ of carbohydrates. Glucose or white bread is used as the comparator. The GI of glucose is taken as 100 and the GI of other foods are given as a percentage of this. Thus, the GI of foods are classified as low GI (less than 55), medium GI (56- 69) and high GI (over 70). The GI multiplied by the amount of the carbohydrate consumed, determines the glycemic load (GL).
Many nutritionists strongly believe in the deleterious effect of consuming diets with high GI and conversely the beneficial effects of taking diets with low GI. There are others who believe that this is too simplistic an approach. Their argument is that carbohydrate is only one of the macronutrients of food and the quality of protein and fat are ignored if only GI is used to assess the quality of a diet.
However, there is a lot of evidence to support the growing importance of the GI and GL of diets. The link between high GI and GL diets to the risk of type 2 diabetes has been clearly established recently. However, what is less known is the association of high GI diets with cardiovascular disease and mortality. The Prospective Urban Rural Epidemiology (PURE) study, of which we are also a part, involves 137,851 participants in 20 countries (including India) in five continents who have been followed for decades. In a paper published in the New England Journal of Medicine in 2021, we looked at the association of the GI and GL of diets with cardiovascular disease. We used country specific food frequency questionnaires to assess the GIs and GLs of various diets in different countries. We reported that diets with high GI were associated with major cardiovascular events including deaths across all ethnicities. This was an eye opener regarding the importance of the GI of foods because until this study was published, it was not known that the importance of GI extends beyond diabetes.
These findings are particularly relevant to India and South Asia where carbohydrate consumption in the form of high GI white rice or wheat, forms the bulk of calories, leading to very high GL of our diets. Hence all attempts should be made to reduce the GI and GL of our diets. This could help, not only in the prevention and control of diabetes, but also to reduce the incidence of cardiovascular disease which occurs at much younger ages in our country.
Examples of diets with low GI include brown rice, steel cut oats, legumes, pulses and beans, fruits like apple and guava, vegetables like spinach, lettuce, brinjal, broccoli, tomatoes, paneer, soya, nuts and seeds.
Diets with high GI include sugar and sweets, white rice, maida, potato, white bread, sweetened drinks, jaggery, cornflakes and cookies.
If diets with high GI, i.e., the ‘bad’ carbohydrates, are replaced with ‘good’ carbs which have low GI and this is combined with adequate physical activity (exercise), it could help to curb the growing incidence of premature cardiovascular disease in India.
(V. Mohan is Chairman, Dr. Mohan’s Diabetes Specialities Centre & Madras Diabetes Research Foundation, Chennai)
