Energy balance in cross-country skiers: a study using doubly labeled water.

Energy intake covering energy expenditure is essential for performance as well as for health aspects in endurance athletes. This study was performed to determine the energy needs for elite cross country skiers during a week of training and to demonstrate whether energy balance could be maintained. Energy intake was calculated from weighed dietary records and doubly labeled water was used to simultaneously measure energy turnover. Average daily energy intake ranged from 15.7 to 20.4 MJ.d-1 in the females and from 25.7 to 36.0 MJ.d-1 in the males. This correlated well with the data for average daily energy turnover (r = 0.96; P = 0.0001) that ranged from 15.1 to 20.2 MJ.d-1 and from 25.4 to 34.9 MJ.d-1, in females and males, respectively. The mean difference being 0.1 (+/- 1.9) MJ.d-1. The close match between energy intake and energy expenditure has not previously been shown in athletes at these high levels of energy turnover. However, if energy intake over separate 24-h periods was compared with corresponding data for training, no significant relationship was found. This indicates that the athletes were not in energy balance during shorter periods. Furthermore, the validity of theoretical calculations of energy turnover, in highly trained subjects, derived from multiples of estimated BMR, is questioned.