This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
If fasting is necessary during lactation, it should be done, but if not necessary it should be avoided, for the reason that it stops the secretion of milk and even the diminution of this secretion resulting from a fast of three or four days is seldom overcome by a return to eating.
If only one of the essential elements of nutrition is withdrawn from the diet of hens, they immediately cease laying. By these means the great amount of food lost to the body through the production of eggs is conserved and life prolonged. A similar thing is seen in fasting mammals in which milk production ceases. In all animals, scarcity of food limits reproduction.