It is also noteworthy that despite the
Walford, 2002.
severe weight loss, none of the four women crew members
missed a menstrual period.
Walford, 2002:
The subjects of the Keys report (all male) suffered lethargy, mental confusion, weakness, and peripheral edema, that is, the classic signs of a starving malnourished population, and they performed no
work activities. None of these signs appeared in the Biosphere 2 crew members, who in fact performed extensive
physical and mental labor throughout the 2 years (1,2). The
degree of physical activity is reflected by the fact that even
on the 1750–2100 kcal daily intake, the lightest woman,
weighing in at 110 lb (50 kg), lost 12 lb (5.5 kg),
whereas the heaviest man, weighing in at 208 lb (94 kg),
lost 58 lb (26 kg). (It is also noteworthy that despite the
severe weight loss, none of the four women crew members
missed a menstrual period.)
Food type and quantity, as well as nutrient content, of the diet in Biosphere-2 can be found in the screenshots below.
Analysis.
The man in the photo below, Walford, one of the study participants, lost too much weight and, as it appears, most of the fat. The lean version of Walford does not look healthy.
It is surprising that women who underwent a similar transformation did not lose a single menstrual cycle. This hints at the role of carbohydrates in the regulation of human hormones. If there is enough carbohydrates in the diet, fertility can be maintained, despite caloric restriction and considerable loss of body mass.
In the picture gallery below, there are some pictures of the Biosphere-2 complex and the study participants.
Biosphere-2 experiment participants experienced an unplanned caloric restriction. 
Note that women participating in the study were actually quite lean. Two of the four women had a BMI of 19. Yet, they all maintained their menstrual cycle during two years of caloric restriction.
The next part is our traditional test that we insert in order to stimulate curiosity and thinking of our readers.
A Test of Physiological Literacy:
1. How do several days of fasting affect follicle-stimulating hormone (FSH) in men in and in women?