For the two days of the year when the Church requires fasting of Catholics (Ash Wednesday and Good Friday), the parameters of the fast are given as: “When fasting, a person is permitted to eat one full meal. Two smaller meals may also be taken, but not to equal a full meal.” Catholics may, of course, eat less, but this is considered the minimum required.
The fasting for Syria on September 7 is not obligatory and so can follow the guidelines of each Catholic’s conscience, ranging from a “black fast” (no food or drink) to a fast of abstinence from one or more items (e.g., no meat, or no dessert, etc.). If one chooses to fast, however, it should be a sacrifice which includes some degree of hunger and self-restraint.
In addition, prayer should be included as part of the fast. Certainly, the prayer for peace in Syria from the USCCB’s website would be appropriate. Other suggestions include praying with Scripture, praying the Liturgy of the Hours, praying the rosary, spontaneous prayer, quiet or contemplative prayer, meditation, etc.