The Glycemic Index was designed for people with diabetes to determine their insulin response to various foods. Those with Type 2 diabetes can avoid foods that may drastically affect their blood sugar level. And, of course, because many are desperate to lose weight, The Glycemic Index also became a popular diet.
To determine a food’s glycemic index, test subjects are given whatever amount of food is needed to supply 50 grams of carbohydrate (carbs). Then, every two hours, their blood sugar levels are measured as it rises then lowers. This determines the glycemic index of that particular food: it receives a ‘rating’ of low glycemic, intermediate glycemic, or high glycemic.
The Glycemic index has been found to be inconsistent. The problem is that 50 grams of carbs in one food might be less or more in quantity than in other foods – and often much more or much less than would be typically eaten. Therefore, in many cases, a high glycemic food can still be safely eaten without blood sugar spikes. In addition, Glycemic index charts were confusing: they seemed to vary widely on each food’s “rating.” There was no consistency in the values listed among different charts.
Researchers at Tufts University found the glycemic index of a given food varied widely among 63 study participants. (This randomized, controlled, repeated test on 63 participants far exceeded the 10 people originally and typically used in the glycemic index methodology.)
Deviations of an average of 15 points in either direction placed a food like white bread, for example, in all three glycemic index categories. White bread was a low glycemic index food (average values of 35 to 55) for 22 of the volunteers, an intermediate glycemic food (57 to 67) for 23 volunteers, and high glycemic (70 to 103) for 18 volunteers. Even for the same individual, glycemic index values could differ by more than 60 points at each trial.
The Glycemic Index does not suggest that a high glycemic index food is unhealthy or that a low glycemic index is healthy (or vice versa). Both glycemic index and glycemic load — a value that adjusts glycemic index to serving size — reflect only food containing carbohydrates. No one eats any of the macronutrients (carbs, protein, fat) in isolation. In a mixed meal, a high-glycemic food’s effect on blood sugar is buffered by any protein or fat in the meal.
The high glycemic index and glycemic load variability reveal limitations, making them unreliable in clinical or private use. There is also the risk of many choosing to avoid healthy foods because they had a high glycemic index and/or glycemic load. For example, ice cream (due to its fat content) has a lower glycemic index than carrots in some charts. It is troubling to think people may opt more often for ice cream over carrots.
The Glycemic Index has been promoted as a weight loss aid, although there is no evidence or sound theory it can consistently do that. People who have lost weight on the ‘diet’ are successful likely due to restricted food intake.
Many sources continue to promote the benefits of choosing foods with a low glycemic index and glycemic load value. However, the Tufts University data suggest those values will not be reliable in designing a daily food plan, especially for healthy individuals. Although it is not a perfect method of rating foods, it can still be used as a tool for people with diabetes as long as it is used sensibly, and its inaccuracy is understood.
Eat smart to maintain or achieve good health. Choose from a wide variety of whole, unrefined foods: vegetables, fruit, legumes, nuts & seeds, and healthy choices of dairy, meats, and fish. It’s wise to get as many nutrients as you can to sustain life – and a wide variety of foods (low glycemic or not) is the sensible way to achieve this.
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Eve Lees has been active in the health & fitness industry since 1979. Currently, she is a Freelance Health Writer for several publication and speaks to business and private groups on various health topics.