This is bad news for teenage girls who skip sleep because although the difference in percentage of calories from fat is small, it can add up over time and cause weight gain.

It has long been known that the amount of muscle in the body is related to bone growth, but the new study shows that fat mass is also important in building bone, particularly in girls.

Breakfast consumption dropped as the girls aged, the researchers found, and those who did not eat breakfast tended to eat higher fat foods later in the day.