The Ninth of Av fast is the same as that on Yom Kippur – nearly 25 hours – but physically it is regarded as the most difficult of the year because it comes at the height of summer, when even those abstaining from food and water move around rather than stay inside air-conditioned synagogues.It begins at 7.41 p.m. on Saturday and ends at 8.09 p.m. the next day.Postponed from Shabbat to Saturday night and Sunday this year, Tisha Be’av requires preparation if you fast, says Magen David Adom. The meal before the fast should include carbohydrates like potatoes or pasta, as well as vegetables and proteins like eggs, fish or chicken. It is best with no salt, sugar or carbonated drinks. Drink a lot of cold water.The elderly and those with chronic diseases should consult with a doctor about whether they are fit to take part in the fast and whether they must continue to take medications. Pregnant women in their third trimester should not fast, according to MDA, which has vast experience from treating hundreds during and after fast days. At any other stage of pregnancy, seek medical advice.Kidney stones might appear during a fast, according to MDA. Headaches, fuzzy vision and, later, difficulty in urinating could mean dehydration, so seek medical help.The Meteorological Service predicts high temperatures all around the country on the fast day, so as much as possible stay in cool rooms or, if outdoors, in the shade. Anyone suffering from chest pains, weakness, respiratory difficulties or excessive sweating, or noting signs of dehydration, should call MDA at 101.MDA recommends ending the fast with a light meal – first a tepid drink, and then a piece of cake or two slices of bread with cheese, for example. Only an hour later should one eat a regular meal.