An interesting program on the t.v. a few years back made more sense to me than anything else.
It was basically a program on fat, conducted by a hospital in the U.S. that is supposed to be the experts in this subject. The nitty gritty of the series basically said two things,
1/ Don't be too concerned with weight, but try to get your cardiovascular system (heart and lungs) fit enough to carry the weight you are, by exercise. The examples shown were two guys each about 18-19 stone in weight and yet were top class triathletes and had shown no health issues whilst training or after and the experts didn't expect them to.
2/ A big fit person, is far healthier than a skinny unfit person.