How long you sleep may affect hormones that regulate appetite and body weight. The large, ongoing Wisconsin Sleep Cohort Study found that people who sleep less, weigh more. Sleeping only four to five hours a night — instead of the recommended seven to eight — alters levels of the appetite-regulating hormones leptin and ghrelin, leading to increased appetite. These hormonal changes combined with having more awake time to eat and feeling too tired to exercise all contribute to weight gain.