THE INFLUENCE OF AN EXCESSIVE MEAT DIET ON FERTILITY AND LACTATION
BMJ (Clinical Research Edition)
THE problem of the falling birth-rate has for some time occupied the attention of medical men and social workers, and various causes have been assigned to account for it. Chief among these may be mentioned the artificial prevention of conception and the later age of marriage, and these, no doubt, play an important part. The results of the present investigation, however, would seem to open up another line of inquiry, and lead me to ask whether the altered conditions of living, and especially the
... and especially the alteration in the constituents of the daily dietary of the people in the form of the increased consumption of meat, may not have an important rOle. It has been shown by Chalmers Watson' that the consumption of meat in this country has rieen from 3 lb. a head per annum in 1850 to 50 lb. a head per annum in 1902. It is within this period that the decrease in the birth-rate has 4rrested attention. It is chiefly the middle and artisan classes of the population which are responsible for our increased meat consumption, and it is noteworthy that the decrease in the birth-rate chiefly affects them, and that there appears to be no diminution in the size of the families of the poorest classes among whom meat is still only a very occasional article of diet. This class incidence, of course, also supports the preventive and late marriage theories, so too much stress must not be laid upon it as an argument in favour of a dietetic cause. Along with the decline in the birth-rate there has been a notable decrease in the number of mothers who nurse their infants on the breast. While the majority of these mothers wilfully shirk their duty for social or other reasons, it is a matter of common clinical experience, and a fact brought out by the report of the Departmental Committee o,n the subject, that a large and increasing number of women are physically incapable of nursing their children because of the poorness of their mammary development and inadequacy of their supply of milk. HIere again my results raise the question as to the possibility of this being due to a dietetic cause. The idea of testing the effect of an exclusive meat diet on the functions of reproduction and lactation was suggested by Chalmers Watson. In a paper on the Influence of Diet on Growth and Nutrition,2 he showed that in rats a diet of ox0 flesh begun when the animals were weaned interfered with the development of pregnancy, none of the four flesh-fed animals having young, whereas all the control animals from the same litter became pregnant. On the other hand it is stated of three families fed on horse flesh from the age of 2j months approximately that all became pregnant, from which he concludes that " the use of this diet in animals of this age appears not. to affect the supervention of pregnancy." He also noted in the meatfed animals which became pregnant that the mammary tissue was less developed than in control bread and milkfed rats. These observations I have extenled, and with a larger amount of material at my disposal am able to amplify his statements and, as regards the question of fertility, to modify them. ,The method of conducting the investigation was as follows: Twelve female rats and several males were put upon a bread and milk diet, and the females were continued on this throughout pregnancy and lactation. These served as the controls. Seventeen females and five males were put upon an ox-flesh diet, but were otherwise under exactly the same conditions as the animals given bread and milk. The animals were begun on a meat diet at various ages, from the second up to the'fourth month, and some of them were kept on the diet for as long as five months. Of the 17 animals fed upon a meat diet only 8 became pregnant, and of these 4 bore young within twenty-one days (the usual gestation period in the rat) of being put on the diet, so that only 4 actually conceived while on meat feeding. Of these latter 1 had been twenty-four, 1 twenty-five, 1 twenty-seven, and 1 thirty days on an exclusive ox-flesh regimen. The other 9 animals, although r T BRIT LMD=ICAL JOURNAL 193 kept for several months, did not conceive, and this in spite of the fact that they were seen to copulate freely right up to the end of the experiment. This reservation must, however, be made, that one of these 9 animals probably had young which were eaten, and it is possible that this happened in other cases. It is not at all probable, however, as the animals were frequently carefully examined, and if there was any indication of their being pregnant were at once transferred to separate cages. Of the twelve animals fed on a bread and milk diet a]) became pregnant and had young; so that we may conclude that a meat diet is decidedly prejudicial to the occurrence of pregnancy in rats when the diet is begun when the animals are from two to four months old. In order to determine whether the fault resided in both sexes or in only one a fresh male-which had been fed on bread and milk was put beside the sterile females which had been on meat for several months. When the animals were killed some days after, one 6f them was found to be in an early stage of pregnancy and must have been impregnated by the male fed on bread and milk. This woulc appear to indicate that the cause of the sterility is partly due to the male, but we have not had sufficient materia) to form any more definite conclusion regarding this. For the second part of the investigation-the effect of a meat diet on lactation-the same animals were used: the twelve controls fed on bread and milk and the eight meatfed animals which became pregnant. The point specially attended to was the weight of the mammary tissue of the animals killed after suckling their young for varying periods. In the nursing rat the mammary tissue forms a continuous sheet spread under the skin of the abdomen 91) each side of the middle line. In addition there are extensions of it into the axillae, up along the neck and into the groins, while in some cases it spreads out so much laterally as almost to reach the back. The nipples are in a double row extending from thorax to the groins. The animals were killed at different periods during lactation. The weight of the mother and the number and weight of the young at the time of death were ascertained. The skin and subcutaneous tissue of the mother's abdomen was immediately removed down to the muscle, care being taken that no mammary tissue was left behind in the axillae or in the groins. The skin was put into 5 per cent. formalin for a few days, when it was quite easy to separate the mammary tissue from the skin on one hand and from the areolar tissue on the other. If an attempt were made to strip the mammae before first fixing in formalin, it was found that a great deal of milk was squeezed out. The immersion in formalin prevented this, although it extracted a small quantity of milk, as shown by its cloudy appearance at the end of twelve hours. It is to be understood, then, that the mammae were weighed out of formalin.