Fasting is the act of willingly abstaining from food and in some cases water, or in other cases from certain food groups.
In Hinduism, a religious fast is observed on ekadasi (the fifth day of each lunar fortnight) and—if observed strictly—involves taking no food or water from the previous day's sunset until 48 minutes after the following day's sunrise.
Among Roman Catholics, fasting often refers merely to abstention from meat on Fridays (see the Code of Canon Law, 1250 to 1253). For Orthodox Christians, fasting at various times refers to abstention from animal products, olive oil (or all oils, according to some Orthodox traditions), wine and spirits (click here for more detail).
Fasting for health reasons typically lasts a week or longer and includes some food intake, such as fruit or vegetable juices.
The political fast (today more commonly known as the hunger strike) seems to be an invention of Mohandas Gandhi. Some people see a difference between a hunger strike, a pure political act, and fasting, a political and religious act. By fasting, they intend to take some of the responsibility of the problem in question.
Hunger strikes have been used by personalities all over the world, including Martin Luther King Jr and Lanza del Vasto (during the Algerian War, Vatican II and the struggle of the farmers of the Larzac plateau).
Today, hunger strikes are often used by refugees seeking asylum.