The current problem with managing bodyweight is that bad or irrelevant data keeps getting plugged into even worse theories. There's an old joke that says the Alabama legislature once tried to simplify the value of pi to "3" because the real value of pi was too hard to teach and understand. Much like high school math when it gets hard, many influential nutritionists have succumbed to simplifying nutrition into something easier to understand and to hell with getting the right results.
Study after study has shown that the Body Mass Index (BMI) is flawed, yet most of the powers-that-be keep using it. The exception is the military, who switched to tape measurements years ago when they found they were losing too many fit, muscular soldiers to the flawed BMI tables. Even non-medical personnel can be trained to use any of several tape measure methods in a matter of minutes. The BMI model is still used however because the data is even cheaper and more plentiful than tape measurements of wrist, waist, neck, forearm, etc.
The calorie counting method of data collection has been shown to be off by as much as 30%; in fact the FDA allows nutrition labels to be off by as much as 20% by law. What's more, there's an erroneous yet prevalent school of thought that says weight can be managed by simply counting calories. The theory is that you'll lose a pound of bodyfat for every 3,500 calorie deficit. Using the 3,500 calorie model, that's a margin of error of 40-80 lbs. per year! The problem is that weight management is just not that simple; the body will attempt to auto regulate its bodyweight in a myriad of ways in response to changes in diet. The real key seems to be finding the food types that set the body's auto regulation system for weight management back on course.
So let's vow to quit using irrelevant data and bad theories just because they're cheap & easy.