A better way to go, then, might be to choose foods based on how much they'll fill you up. To this end, we're kind of flipping over Self Nutrition Data's new rating system, called Fullness Factor. Compiling data from a number of studies, researchers have come up with a formula that calculates the "satiety index" of different foods, given the calorie, protein, fiber, and fat content of each. With those calculations, the team then ranked common foods based on how satisfying they are per calorie.
So, which edibles got high marks? Some of the biggest satiety stars were pretty predictable, like lentils, apples, popcorn, and potatoes. But, oranges, grapes, and bean sprouts also took high honors — probably because they contain so few calories per unit. Even more surprisingly, many foods we commonly think of as filling (most notably brown rice and nuts) scored low satiety index numbers.
Of course, the Fullness Factor system is conceptually similar to the Glycemic Index, which measures the effect of certain foods on your blood sugar. But, while the Glycemic Index only applies to carbohydrates, the Fullness Factor can be calculated for any food you can think of — as long as you have its protein, fat, fiber, and calorie counts. Yes, it's a lot of math, but I'd choose that over a post-kale empty tank any day.