Night owls, or people who stay up late on a regular basis, might be more likely to develop diabetes and heart disease because they don’t burn fat well. In a new study published in the journal Experimental Physiology, researchers at Rutgers University divided over 50 middle-aged adults into either early birds or night owls. They analyzed each participant’s activity for a week as well as their use of fuel for daily activities and exercise. The night owls burned less fat and tended to use carbs as their energy source. The early birds, on the other hand, burned more fat than night owls did, both at rest and during exercise. They also tended to be more active during the day.