When a person does not get enough sleep, impulse control decreases and the tendency to store fat increases.
Adam Rifkin stashed this in Sleep!
Peer-reviewed article: "Sleep restriction decreases morning resting metabolic rate in healthy adults, suggesting that sleep loss leads to metabolic changes aimed at conserving energy."
Other studies have found that when people are subjected to sleep deprivation, they increase consumption of foods that we associate with fat storage (calorically dense and high in saturated fat and sugar). As impulse control is reduced when an individual is under stress, such as when a person is sleep deprived, the ability to restrict calories is reduced. On top of this, the body tends towards fat storage when the metabolic rate is compromised. This short term study only highlights the first in a chain of concerning physiological changes that damage energy regulation during sleep deprivation. The overview (that builds off of other studies) is that when subjected to sleep deprivation, impulse control decreases and the tendency to store fat increases.
So getting enough sleep helps willpower and weight.