When you hear the word diet, the first thing that comes to mind is food and exercise. This makes perfect sense considering energy balance (Calories in vs Calories out) is the main determinant of weight loss; however, one thing that is almost always overlooked is sleep. How does sleep affect dieting?
Study: Short sleep duration increases energy intakes but does not change energy expenditure in normal-weight individuals 
Fifteen men and fifteen women, ages 30-49 were studied under 9 hr/night sleep conditions for five nights, and 4 hr/night sleep conditions for five nights. Food intake and energy expenditure was measured on day five for each condition.
Participants consumed approximately 300 more Calories while getting 4 hr sleep/night. Total daily Expenditure (TDE) was decreased by 22 Calories while getting 4 hr sleep/night. This study was short term, so long term conclusions can't be drawn from this study alone. If that trend had continued, it would equate to almost a pound of weight gain (or prevented weigh loss) per week.
Study: Impact of insufficient sleep on total daily energy expenditure, food intake, and weight gain 
Eight men and eight women ages 18-27 were studied both under 9 hr/night sleep conditions for three nights, and 5 hr/night sleep conditions for five nights. Food intake and energy expenditure was measured each day.
The participants in this study consumed approximately 200 more Calories in the 5 hr condition. Both groups gained weight during this study; however, participants gained 1.8 pounds in the 5 hr condition vs 0.5 pounds in the 9 hr condition. Ghrelin (a hormone that signals hunger) decreased by 21% in the 9 hr condition which led to participants feeling less hungry in the 9 hr condition.
While sleep may not directly impact metabolism, it does increase hunger, making it harder to stick to a diet. As I have stated many times in the past, adherence is the most important factor in reaching your fat-loss goals. You should definitely aim to get around 7-9 hours of sleep each night, especially if you are dieting.
Thanks for reading! Join me next week for another helpful fat loss article. As always, God bless you AND your family and I'll see you next time!
 St-Onge, M. P., Roberts, A. L., Chen, J., ... Jones, J.H. (2011) Short sleep duration increases energy intakes but does not change energy expenditure in normal-weight individuals. American Society for Nutrition, 94(2), 410-416, doi: 10.3945/jcn.111.013904
 Markwald, R. R., Melanson, E. L., Smith, M. R., ... Wright, K. P. (2012) Impact of insufficient sleep on total daily energy expenditure, food intake, and weight gain. Proceedings of the National Academy of Sciences of the United States of America, 110(14), 5695-5700, doi: 10.1073/pnas.1216951110