More than 90 percent of Greeks are members of the Greek Orthodox Church, and faith plays an important role in Greek life. The Greek Orthodox faith observes several fasts during the year, which means abstinence from foods derived from animals containing red blood (cephalopods are allowed, since they do not have red blood), from dairy products, and at times from olive oil, and wine as well.
Strict observers of all fasting periods and fast days will follow these guidelines for over 180 days a year.
Total fasting (no food at all) is reserved for a period of time before taking Holy Communion. 

Foods allowed during fast periods are called nistisima (νηστίσιμα, pronounced nee-STEE-see-mah) and they are eaten during the Great Lent and other fasts. The Greek Orthodox Paschal (Easter) season starts with The Great Lent, beginning on a Monday (Clean Monday) seven weeks before Easter Sunday. The Greek Orthodox faith. The weeks of the Great Lent are: 

1. First Sunday (Sunday of Orthodoxy)
2. Second Sunday (St. Gregory Palamas)
3. Third Sunday (Adoration of Cross)
4. Fourth Sunday (St. John of Climax)
5. Fifth Sunday (St. Mary of Egypt)
6. Palm Sunday through Holy Saturday and Easter Sunday

 

Fasting

Greek Orthodox Lent is a time of fasting, which means abstaining from foods that contain animals with red blood (meats, poultry, game) and products from animals with red blood (milk, cheese, eggs, etc.), and fish and seafood with backbones. Olive oil and wine are also restricted. The number of meals on each day is also limited.