(The following is excerpted from my dissertation, for the reference of those who would like some historical background on Lenten practices in the United States.)
Prior to 1917, general law of the Church required fasting on all the days of Lent, excepting Sunday. This fast included one meal a day, abstinence from meat, and abstinence from eggs and milk.
In 1886, Leo XIII in Indultum Guadragesimale permitted the faithful of the U.S. to use meat, eggs, and milk products at all meals on Sundays during Lent, at the principal meal on Monday, Tuesday, Thursday, and Saturdays, excepting Saturday of Ember week and Holy Week. It also allowed for the use of eggs and milk products at the evening collation daily during Lent and at the principal meal when meat was not allowed. Indultum Quadragesimale also allowed for the use of eggs and milk products at the evening collation daily during Lent and at the principal meal when meat was not allowed. Indultum Quadragesimale further allowed a small piece of bread in the morning with a beverage, the possibility of taking the principal meal at noon or in the evening, and the use of lard an meat drippings in the preparation of foods. Those exempt from the law of fasting were permitted to eat meat, eggs, and milk more than once a day.
The 1895 so-called “Workingmen’s Privilege” allowed the bishops in the United States to permit the use of meat in circumstances where there was difficulty in observing the common law of abstinence, excluding Fridays, Ash Wednesday, Holy Week, and the Vigil of Christmas. This workingmen’s privilege (or indult) allowed only for meat once a day during Lent, taken at the principal meal, and never taken in conjunction with fish. This particular indult was extended not only to the laborer but to his family as well. The motivation of such an indult was no doubt to allow for enough sustenance such that the many Catholic immigrants to the U.S. who worked as manual laborers could perform their difficult, energy-demanding physical work without danger to their health. Moreover, those with little variety in terms of food options would not have it unnecessarily further narrowed.
After the 1917 Code, there were some additional documents modifying fast and abstinence rules, particularly to accommodate difficult wartime conditions that included limitations in food availability. In 1917 Pope Benedict XV granted the faithful of countries in World War I the privilege of transferring Saturday Lenten abstinence to any other day of the week, excepting Friday and Ash Wednesday. In 1919 Cardinal Gibbons was granted his request of transferring Saturday Lenten abstinence to Wednesday for all bishops’ dioceses in the U.S. This permission, as well as the workingmen’s privilege, were frequently renewed, but, after 1931, this was permission was only on the basis of personal requests from individual bishops. During World War II in 1941, Pope Pius XII granted to all bishops the power to dispense entirely from fast and abstinence, excepting Ash Wednesday and Good Friday. He extended this again in 1946. In 1949, several years after the close of World War II, Pius XII placed some restrictions on the earlier granted dispensations, once again requiring yearlong Friday abstinence, fast and abstinence on Ash Wednesday, Good Friday, and the Vigils of Assumption and Christmas, but allowing eggs and milk products at collations on days of fast and abstinence.
In 1951, the bishops prepared a report on the state of Fasting and Abstinence in the U.S. for a bishops’ conference. In it they wrote:
We earnestly exhort the faithful during the periods of fast and abstinence to attend daily Mass; to receive Holy Communion often; to take part more frequently in exercises of piety; to give generously to works of religion and charity; to perform acts of kindness toward the sick, the aged and the poor; to practice voluntary self-denial especially regarding alcoholic drink and worldly amusements; and to pray more frequently, particularly for the intentions of the Holy Father.
The commentary that followed these regulations gave an account of the special faculties granted by the Holy See to bishops in the U.S. Of particular importance was Pius XII’s 1949 decree that set forth a minimum of abstinence and fast for the faithful throughout the world, regardless of prior indults; these regulations were abstinence on all Fridays, fast and abstinence on Ash Wednesday, Good Friday, and the vigils of the Assumption and Christmas. However, this decree also allowed local ordinaries the authority to determine when to dispense from fast or abstinence.
Pius XII’s decree also gave the bishops the authority to determine how best to apply the workingmen’s privilege (or partial abstinence). The U.S. bishops chose to extend this indult to all the faithful in the U.S. in 1951 when they updated the fast and abstinence regulations. The workingmen’s privilege was a relative norm wherein a fast day was defined as allowing one full meal and two collations which together did not total a full meal. The relative norm had long been in use in Europe, until the absolute norm of two ounces (first collation) and eight ounces (second collation) was introduced by Alphonsus Ligouri to assist the scrupulous in deciding how much food they were allowed on a fast day. The bishops thought that the relative norm allowed for the person to take enough food to do his daily work properly, and hence the relative norm “makes it possible for most persons to fast, whereas…most persons cannot fast according to the ‘absolute norm.’” In some places, such as Ireland, a modified relative norm allowed for one full meal (the size of which was to be determined by the individual) and two collations totaling no more than 12 ounces, or 18 total ounces of food for those who needed the sustenance to perform strenuous work. By 1950, however, many other countries had agreed upon uniform fast and abstinence regulations for their regions by also sanctioning the relative norm.
This and the other regulations detailed in the 1951 report were still in effect up until 1966, with a few modifications.
 “Report on Fast and Abstinence,” 5.
 “Report on Fast and Abstinence,” 7.
 It would be interesting to know how many people had access to the weight measurement that would be required by this absolute norm and how this amount compared to the amounts consumed by those using the relative norm.
 “Report on Fast and Abstinence,” 10.
 “Report on Fast and Abstinence,” 14.
 “Report on Fast and Abstinence,” 13-19.