of course losing weight is great for people who lose it.it prevents lots of things:diabetes,atherosclerosis,and many other medical problems,and has alot of benefits for the long term(even though ome of there researches are biased,but i'm, not going to get into that). in certain cases people who have medical problems should definitely try to lose weight(i believe it should not be done alone,but with a medical adviser).
but i think it's wrong to say that everyone who is overweight should try to lose weight. there is a differance between BMI 25-30 ,than 30 and up. i've actually read an article that says that people in that range of BMI are healthier than the "normal weight" so it's not so black and white. besided- weight isn't everything.the distribution of the fat is what matters- the amount of visceral fat(abdominal weight gain,as opposed to fat in the thighs). people with BMI 30 that their cholesterol lever low,and there blood pressure is not even close to prehypertension,even healthier than me,why should they try to lose weight?
i disagree with your claim that everyone who is overweight should try to lose weight.
when you say success-what do you mean?because within a year 1/3- 2/3 gain all the weight back,and after 5 years- nearly 95% gain their weight back or even more than what they lost(aren't you familiar with the statistics? )-is it worth it?it's very individual.
what i'm suggesting,is that more research should be done about how to achieve that goal(maintenance!!!not losing-losing is much easier),before telling everyone with BMI above 25 to lose weight.there are some articles in the national weight control regitry's internet site.
if you read the article: "change in energy expenditure resulting from altered body weight"
by leibel et al. in the nejm,it explains why it's so hard to maintain the weight loss.
i claim that there's not enough research done about the negative outcome of weight loss(and one of the reaons is that alot of people make money from making people believe that the less they weigh the better-they have too much power).
to sum things up not everyone is the same,and it's a problem to tell everyone who's overweight to lose weight.you have to weigh the benefits against the negative outcomes for each individual person before you advise someone to lose weight.in order to determine who has a higher chance to succeed,more research has to be done.
the advice to the pulic should be to eat heathy food,do more exercise,but the focus shouldn't be on losing weight,because anyways 95% will gain most of it back,or even more-so they might as well just maintain their weight(and if someone really has to lose weight-it should be monitered by a physician-but that's a different issue).