Most healthy adults need seven (7) to nine (9) hours of sleep each night.  Don't fall prey to the TV commercials that claim to help you get "a better 6".  That is just not enough for most adults.

Insufficient sleep also undermines weight-loss.  A study in the Annals of Internal Medicine concluded that "The amount of human sleep contributes to the maintenance of fat-free body mass at times of decreased energy intake. Lack of sufficient sleep may compromise the efficacy of typical dietary interventions for weight loss and related metabolic risk reduction."