Related studies have found that people who sleep less than 7 hours per day are generally fatter than people who sleep longer. This is because lack of sleep affects metabolic functions, increases appetite-stimulating hormones, and reduces the level of hormones that produce fullness. This will definitely lead to:. ['Fat people have better appetite than normal-weight people.', 'Sleep conditions affect metabolism.', 'Hormones affect appetite.', 'Hormone levels of fat people may be different from ordinary people.']