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Diet Diary: Decoding contradictory studies on glycemic index

Glycemic index classifies carbohydrate-containing foods according to potential to raise blood sugar levels.


Scientific research is the foundation of modern medicine. Yet, when it comes to media reports, several things that have been reported one day are countered sooner than later by another study, confusing the reader. For example: coffee is good for health, milk is good for you but bad for the heart; high protein is good for weight loss but bad for your heart, fats are bad for the heart but good for health.

Recently, a report on the glycemic index of food happened to create a similar controversy. The glycemic index classifies carbohydrate-containing foods according to their potential to raise your blood sugar levels. Whole grains, legumes, vegetables, fruit, low-fat dairy products, nuts and seeds raise blood sugar slowly and have a low glycemic index. Low glycemic carbohydrates help you lose weight and keep you feeling full longer, improve insulin sensitivity, blood lipids and blood pressure.

However, a scientific study recently contradicted these findings. Published in the Journal of the American Medical Association in 2014 conducted on 163 overweight adults for duration of five weeks, it stated that diets with low glycemic index, compared with high glycemic index of carbohydrates, did not result in improvements in insulin sensitivity, lipid levels, or systolic blood pressure. This also implied that it had no benefit in body weight and obesity management. There were some drawback in this study – that it is a relatively small (163 participants), short (five-week) randomized controlled trial and the study population was not representative of the general population of most countries.

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Several studies of longer duration conducted on much larger and diverse samples and meta-analyses have stated benefits of consuming a healthy low GI diet in relation to blood glucose, insulin and lipid profiles, weight loss and prevention of diabetes and heart disease. One of the largest clinical trials of GI involving 773 European adults, published in 2010 in The New England Journal of Medicine reported that a low GI diet was found to be highly effective in preventing weight regain over 6 months.

The beauty of scientific research is that it is a dynamic process that moves forward slowly and recommendations are made based on the best science available at the time. However, with new research and new results, these recommendations may be revised. The research process is like placing stones on an old-fashioned balance scale. When enough weight accumulates on one side, the scale tips in favour of a particular recommendation. And the more weight there is on one side, the stronger the recommendation is and the more evidence it would take to change it.

The important thing to remember is often just one study becomes a headline or a 30-second sound byte that may be oversimplified, distorted or overstated. Accurate reporting with perspective is crucial if confusion is to be avoided. Try and get to the original scientific article whenever possible.


So, the jury is clearly in favour of distinguishing the carbohydrate quality according to their glycemic index. However, nothing in isolation can ever be effective and over-simplification of any concept can be erroneous and unhelpful.

So, a holistic and balanced approach to a good diet is the prudent approach and there is no magic bullet.

Ishi Khosla is a former senior nutritionist at Escorts. She heads the Centre of Dietary Counselling and also runs a health food store. She feels that for complete well-being, one should integrate physical, mental and spiritual health. According to her: “To be healthy should be the ultimate goal for all.”

First published on: 10-01-2015 at 00:49 IST
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