Kate Greene participated in a mock Mars mission and found that female crew members expended less than half the calories of the male crew members. Less than half! They were all exercising roughly the same amount—at least 45 minutes a day for five consecutive days a week—but their metabolic furnaces were calibrated in radically different ways.
During one week, the most metabolically active male burned an average of 3,450 calories per day, while the least metabolically active female expended 1,475 calories per day. It was rare for a woman on crew to burn 2,000 calories in a day and common for male crew members to exceed 3,000.
The calorie requirements of an astronaut matter significantly when planning a mission. The more food a person needs to maintain her weight on a long space journey, the more food should launch with her. The more food launched, the heavier the payload. The heavier the payload, the more fuel required to blast it into orbit and beyond. The more fuel required, the more expensive the launch becomes.