Conventional wisdom is that a calorie is a calorie, no matter when you eat it, and that weight gain is caused by eating more calories than you use. Nutritionists call this the calories in, calories out theory of weight control. But it might not be as simple as that. New research discovers that what time you eat may play a significant role in gaining weight.

According to this study, eating a late dinner is associated with weight gain and high blood sugar levels, regardless if the meal is the same that you would have eaten earlier.

“We were aware of other research that suggested that late eating is associated with obesity, and because the association is not the same as causation, we wanted to look at this in a more rigorous way,” study author Dr. Jonathan C. Jun, associate professor of medicine at Johns Hopkins University told Healthline. Jun explained that the research team wanted to understand whether late eating actually changes metabolism in a way that promotes obesity.

To do this, Jun and the team studied 20 healthy volunteers (10 men and 10 women) to find out how their bodies metabolized dinner eaten at 10 p.m. instead of 6 p.m. All study participants went to sleep at the same time: 11 p.m.

Study findings show that blood sugar levels are higher, and the amount of fat burned lower, when eating a late dinner, even when people ate the same meal. The study found that late eaters had peak blood sugar levels almost 20 percent higher and fat burning reduced by 10 percent, compared with those who ate dinner earlier.

According to researchers, this is strong evidence that eating a late meal causes weight gain even if you don’t increase the calories consumed.