dieting has different effects on men and women
one factor affecting the body's rate of metabolism is the amount of muscle mass, of which men have more.
your body requires a certain amount of calories daily to survive. if you consume fewer calories that what your body requires to sustain itself, your body will go into STARVATION mode, in which your metabolism slows down, your body burns calories at a slower rate, and you energy levels decrease. your body breaks down muscle before it breaks down fat. this is not good because muscle is much denser than fat, which roughly means it occupies less space.
since men have more muscle mass, they require a higher minimum amount of calories daily. so dieting doesn't really work as effectively for men.
smoking is related to weight loss because nicotine curbs your appetite. you eat less, then you start from the top as described above.
i am NOT a DOCTOR but it is roughly something like that lah...