Disruptions to the body`s internal clock caused by shift work or jet lag can cause changes in metabolism leading to a higher risk of obesity and type 2 diabetes, according to a new Harvard Medical School study. Although most studies of sleep disruptions on metabolism last only one or two weeks, this study lasted five weeks to see how chronic changes to sleep cycles affect metabolism. The researchers examined the health effects of interfering with the circadian rhythms of 21 male and female participants, controlling when and how much they ate, slept, and exercised. They found that the resting metabolic rate of participants at the end of the study was eight percent lower than at the beginning of the study, which could cause a 10-pound weight gain if exercise or diet are not modified to compensate. Reversing the participants` circadian rhythm by having them sleep during the day and stay awake at night also resulted in poorer quality sleep and less insulin was produced in response to meals causing blood sugar levels rose so high in some participants that they became per-diabetic. Previous studies show that sleep deprivation can cause insulin resistance, but does not change the amount of insulin the pancreas produced. Both problems can contribute to an increased risk of type 2 diabetes. “If you’re not getting enough sleep, then it’s hard to find the energy to exercise,” says lead author Orfeu Buxton. “And if you’re not getting enough sleep, you not only eat more than you need but you tend to make poorer food choices.”