Stress on a woman's body is more apt to stop her menstrual cycles then to enhance her fertility. It is a survival mechanism.

During times of high physical stress even without the presence of malnutrition a woman will cease her cycles. This is seen often in women athletes. The body reacts in much the same way to intense emotional stress.

As for the "medical" data gathered during the Nazi's regimen in WW2, it must be remembered that the men performing these experiments were intent on proving race superiority. That the data may be skewed by these views have to be considered.