Question

How does Sleep-deprived lead to an increase in appetite and reduce energy expenditure? (must include ghrelin and leptin in the discussion)

Answer 1

Circadian rhythm respond primarly to light and darkness in an organisms environment. Sleeping at night and being awake at day time all comes under circadian rhythm. Studies had found that a chronic disruption in circadian rhythm (day/night cycle) leads to weight gain , impulsivity and other behavioural changes.

Sleep requirement varies from person to person, but for most healthy adults about 7-9 hours of sleep at night is needed for proper metabolic activity in the body. Sleeping at night for less than 5 hours is found to affect the individual with excess weight gain and obesity. The function of hormones such as leptin and ghrelins are found to have association  with sleep. Leptin is an adipocyte-derived hormone that suppresses appetite. The hormone triggers a series of messages and responses that starts in hypothalamus. During sleep at night the leptin level increases and it conveys the message to brain that there is plenty of energy for time being and suppresses the feeling of hunger. Insufficient sleep is associated with a decrease in this satiety hormone leptin. Too little leptin in body makes brain to think there is need of energy. At this time another hormone called ghrelins come to action. Ghrelin is predominantly a stomach-derived peptide that stimulates appetite. During normal sleep, levels of ghrelin decrease, because sleep requires far less energy than being awake does. When people are awake at night with insufficient sleep leptin level goes down and ghrelin level increases which result in hunger and food intake. This increase in energy input  than energy output which result in high BMI (body metabolic index) and obesity.

Sleep depreviation also increases the level of stress hormones and insulin resistance which ia also a cause for weight gain.