If you’re one of those people who can’t stand all the counting and tracking and adding and charting that some diets require, you could find a refuge in one simple numerical scale: the glycemic index. On the other hand, you might find it another maddening way to complicate the simple act of eating.

The glycemic index is a measure of the quality of carbohydrate foods. It’s kind of a good carbs/bad carbs thing, based on how they affect your blood sugar. Though it’s not new, it did start getting a lot of press when the anti-carb movement took hold.

It works like this: in the glycemic index , pure glucose is arbitrarily assigned the score of 100; it doesn’t mean anything in particular; it’s just a set reference point for how it has affected the blood sugar by about two hours after eating. Then all other foods in the index are given a number relative to glucose and its affect on the blood sugar.

Foods with a low index typically break down slowly and don’t cause drastic fluctuations in blood sugar. Foods with a high index typically do. For instance, green peas have an index of 39, while corn flakes have an index of 92.

Originally developed to help folks—particularly diabetics—control their blood sugar, the index includes mainly carbohydrate foods, because protein and fat don’t have much immediate effect on blood sugar.

But assigning numbers to different foods based on their glycemic effect just happens to create a scaled list of foods that ends up being a very useful tool for people dealing with obesity and other health issues, as well. That’s because simply maintaining a low-glycemic index diet tends to guide people toward healthier eating and weight loss, even when that is not their specific goal.

Consider: Type II diabetes, as well as various cancers and cardiovascular disease, are all highly correlated with high index diets. There’s abundant research that shows that reducing the overall glycemic index also reduces the risks of those problems.

That’s because almost by default, a low-index diet will include more fresh fruits and vegetables, more fiber, more dairy, all foods that offer essential nutrients, that are more likely to be lower in calories and which tend to keep the body sated longer, holding off the next hunger spell. All that usually adds up to weight loss, no matter what the program.

Proponents of the index say it’s more helpful than counting calories or grams of fats or carbs, and actually offers a simplified approach to learning to eat better, but some experts caution that people shouldn’t get too wrapped up in worrying about the precise numbers. Instead, they urge that people pay attention to whether the foods they’re eating have a low, medium or high index.

That’s because, as with any rule, there are exceptions to the fairly consistent physiological rules that underlie the index. For instance, watermelon has a pretty high glycemic index, about 75, which is even higher than table sugar. Does that make it bad for you? No. Because in spite of its high index, watermelon actually has a pretty low glycemic load. That’s a measure based on the amount of food you’d actually consume, not just an arbitrary quantity used in testing, as with the index.

The glycemic load of a food can be determined using the glycemic index number for a food, divided by 100 and multiplied times the available carbohydrate you’d eat. With most foods, low index is consistent with low load, but there are the quirky exceptions. Of course, to find them, you’d be back to doing a bunch of math again, and that’s just not the way people normally eat.

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