Brace yourselves for a study which produced results which are, to say the least, counterintuitive. A group of Finnish researchers found in an epidemiological study on twins that those overweight people who intended to lose weight who lost weight were most at risk of dying over the study period. (the higher the hazard ratio the greater the risk of dying).
But don't rush to conclusions. Epidemiologist Meir Stampfer of the Harvard School for Public Health says epidemiology studies of the effect of weight on mortality need to correct for a number of problems.
I take all of this to indicate that not becoming overweight in the first place is a good thing - but then you knew that already, right?