Although most people would agree that sleep is important from a health perspective, it also plays a role in body composition.
Sleep deprivation can hinder your physique goals for multiple reasons.
- Sleep deprivation can severely disrupt your appetite
To test the impact of this, one study compared 4 hours versus 8 hours of sleep time and found that shorter sleep duration coincided with higher levels of hunger and a 559 calorie (i.e. 22%) increase in food intake, on average . On top of an increase in appetite, it makes sense that sleep deprivation may cause greater food intake as being awake for longer is essentially a wider opportunity to eat.
For example, without factoring in potential changes to physical activity, if you are awake for 20 hours per day it makes sense that you would likely consume more food than if you were only awake for 16 hours per day.
- On top of changes in appetite, sleep deprivation can also modify how much body fat you lose during a dieting phase.
One study compared 10-day periods where bedtime was designated as either 5.5 or 8.5 hours per night . All subjects were consuming a reduced calorie diet. Although weight loss was similar in both groups, the shorter sleep duration resulted in less body fat lost and more lean body mass lost. This obviously isn’t ideal for people who are seeking aesthetic goals.
With the same calorie deficit (90% of resting metabolic rate), subjects lost comparable amounts of weight (3kg) but subjects who only slept 5.5 hours lost 0.6kg of fat versus 1.4kg.
Of course, some people may find it more difficult to achieve longer sleep durations (long working hours, waking up in the night etc) so how someone could improve their sleep quality and duration is a harder question to answer.
It is just worth keeping in mind that prioritizing sleep can significantly improve body composition at no extra cost.
 Acute partial sleep deprivation increases food intake in healthy men