Otago study questions value of glycemic index

Potatoes and other reportedly high-GI foods might not be the dietary villains that recent publicity, books and health-based programmes would claim them to be, a new University of Otago study suggests.

The study, of 30 healthy adults aged from 18 to 50, by Hayley Dodd, Dr Bernard Venn and colleagues from Otago’s Department of Human Nutrition, found that it was difficult to predict the actual Glycemic Index (GI) values of mixed meals for individuals eating them, even if the GI values of the individual parts of the meal were known.

The Glycemic Index is a measure of the effects of carbohydrates on blood sugar levels.

Normally, individual foods are tested for GI and it is less usual to test the GI of a whole meal. However, in this study, the GIs of three meals were tested – the meals all contained chicken, peas, carrots, kumara and gravy, together with a starchy staple food varying between potato, white rice or spaghetti.

The researchers found that the GI for each meal was not as high as anticipated. From the GIs of the foods used the researchers expected that the potato meal would have an overall GI of 65, which falls within the medium range; instead at 53, the meal fell just within the low range. Therefore, although potato is a high-GI food, a meal containing potato is not necessarily so, Dr Venn says.

“I don’t think people should be too afraid of putting high-GI foods into their meals – our work suggests that having a small amount of potato with a meal isn’t going to drive your blood sugar crazy,” he says.

The research has been published in the October issue of the prestigious American Journal of Clinical Nutrition.