My older sister and I have both struggled with serious weight problems our whole lives. I have went from fat -> skinny twice in my life but my sister has done it probably 6 or 7 times. She is in her 40’s. She has went from over 200 pounds to about 130 several times. She understands how to lose weight and has done it successfully at least one time in her life.

She is more successful at dieting than people who have been overweight their whole lives and know they should lose weight, but yet have never actually done so, not even once. My question today is what percentage of obese people fall into that category?

i.e. what percentage of obese people have a sufficient desire or motivation to lose weight but have never succeeded, not even temporarily. By obese, I mean the definition of having a BMI higher than 30, which works out to at least 40 pounds overweight for an average-height person (if my back of envelop math is correct).