If one reviews the current literature as presented in the text-books on the effect of menstruation on breast milk he is struck with the fact that opinions are very diverse and that many statements are made without sufficient scientific foundation. In an endeavor to obtain scientific facts on this subject we quite carefully looked through the literature and were able to find only a few articles of any scientific value.
In 1853 Vernois and Becquerel1 in three cases examined the milk secreted before and during menstruation. They found that taken as a whole there was a lower specific gravity with a decrease of water and sugar content and an increasing total solid and casein, while the fats and ash remained about the same during the menstrual period. But a closer inspection of their cases shows that while Cases 1 and 3 agreed with these findings, Case 2 showed opposite
GRULEE CG, CALDWELL FC. THE INFLUENCE OF MENSTRUATION ON BREAST MILK. Am J Dis Child. 1915;IX(5):374-380. doi:10.1001/archpedi.1915.04100470023003