Earlier quoted context omitted.
I'll vouch for the effectiveness of losing 30+kg (65+lb). Which only reduces the back pain problem for overweight people to a known-intractable weight loss problem... :-/
Weight loss isn't "known intractable". Physically it's very simple, if an overweight person is physically prevented from eating too much, they'll lose weight, just like physically it's very simple to quit addictive drugs. And the drug analogy is a good one, because just like quitting drugs, you can't quit overeating (barring the aforementioned option of someone physically preventing you from doing so - which is liter…
Indeed, weight loss is "simple", as you said. The problem arises when you have managed to get to your target and you realize that, short of amphetamines or similarly dangerous drugs, there is no known way to keep your weight stable with an acceptable life quality.
Obese people are not stupid when they choose to keep eating; they've just learnt by experience that, unless you solve the hunger problem, loosing weight will not yield a better life.
By the way, surgery actually looks like an option.