Changes in the food habits of large groups of persons may be brought about by necessity and likewise by altering customs and food preferences. Conditions determined by the war and consequences arising from it have enforced pronounced changes in the dietaries of thousands. What the outcome of this necessary response to the exigency of food situations may be is now being exemplified in the effect of the innovations on the health of the affected nations. Scurvy, beriberi and war edema are conspicuous illustrations of the extreme effects brought about by necessity, that is, by actual shortage of certain foods or by their high cost. A few months of deprivation may suffice to send deficiency diseases broadcast among people previously living in good health and working efficiency.
The other category of change in food habits by which new dietary customs come into vogue and older choices lose their popularity is slower