The US Nurses Health Study monitored women for 16 years keeping records of their weight and sleep patterns. Those who slept less than five hours a night were 32% more likely to "experience major weight gain." There was no mention of the usual associated three hour late-night-chunky-chocolate-chip-ice-cream-diet-plan.
Of course these findings are sure to create a whole new series of "your mamma such an insomniac" jokes.