"Shift work goes against our fundamental biology," Wright, also an associate professor of integrative physiology, said in a statement.

"Shift work requires our biological day to occur at night and our biological night to occur during the day and that's very difficult to achieve because the sun is such a powerful cue. We can have some change in our clock -- a couple of hours -- but then on days off, it goes right back. Shift workers never adapt."

The research team, however, was surprised to find that the study participants burned more fat when they slept during the day compared to when they slept at night.

It's not clear why this happens, Wright said, but it's possible the extra fat-burning is triggered by the transition day between a daytime schedule and a nighttime schedule.

He cautioned that this would not lead to weight loss because the total energy expenditure over the three days of shift work was lower.

Further research is needed before specific recommendations can be made for how to improve the health of shift workers, Wright said.

"What we can say is that it's perhaps even more important to have a healthy diet for shift workers as well as a healthy amount of physical activity," he said.