Ever feel guilty when you bite into a baked potato or a piece of watermelon, wary either will send your blood sugar sky high? Blame the rhetoric of the glycemic index (GI), a system introduced in 1981 that rates foods based on how much they raise blood-glucose levels. It was originally developed for diabetics, but the GI has bled into the mainstream and helped bolster popular diets like Atkins, South Beach, and NutriSystem. But it's also been dogged by controversy—and questions as to whether it's an effective way to choose healthy foods. Case in point: That baked potato has a high, blood-sugar-spiking GI of 111. A slice of frosted Betty Crocker vanilla cake, on the other hand, has a low GI of just 42. Does that mean the Betty Crocker is better? No, of course not.
Now, a new study from the Harvard School of Public Health may make the GI seem even more dated. The research, published in JAMA, found that following a low GI diet did not result in improvements in insulin sensitivity (a marker for diabetes), cholesterol, or systolic blood pressure for 163 overweight adults.
The factor that did make a difference? The amount of carbohydrates the study participants ate. When participants consumed a low-carb diet for 5 weeks, regardless of whether it was high or low on the GI, they lowered their total triglycerides (a type of unhealthy blood fat) by about 20% compared to those who ate high-carb diets for the same amount of time. The amount of carbs did not affect insulin sensitivity and only slightly affected blood pressure. Low-carb diets were associated with a one-point drop in diastolic BP.
The bottom line: if you're not diabetic, the GI should not be your go-to criteria at the grocery store. Instead, consider a food's total nutritional profile, including total sugar and ingredients list—important factors that lead to healthy choices every time.
Author: Caroline Praderio