Rovira i Virgili University research in July 2019 found that, “individuals with highly variable sleep patterns - that's to say, who did not sleep the same number of hours every night - at the beginning of the study lost less weight after a follow-up period of 12 months. What is more, a high sleep variability and sleeping little - less than six hours - a day was associated with a lower decrease in body mass index and waist circumference.”