Tisha B'Av is the saddest day in the Jewish calendar. Tradition holds that both Temples were destroyed on this day. The spies defamed the Land of Israel and the expulsion of the Jews from Spain was decreed.
We read the book of Eichah (Lamentations), fast for a full day and observe the other strictures of mourning.
Here are some suggestions for an easier fast:
If you drink coffee or other caffeinated beverages regularly, start tapering off a week before the fast. This should help minimize or avoid caffeine-withdrawal headaches.
Drink plenty of water – even more than you're used to, starting several days before the fast. If you live in a hot climate, this is especially important.
For a day or two before the fast, avoid eating heavily salted, spicy and fried foods.
Eat a light meal just before the fast, including protein, carbohydrate and a little fat. Fish is a good main-course. Add pasta, potato or a cooked grain, vegetables, and fruit for dessert. Herbal tea is a relaxing way to finish the meal.
After the fast, don't stress your system by eating too much. Some people like to break the fast with tea and cookies or a bit of cake, followed a little later by dinner. My preference is for a light, simple dairy meal. Blintzes, a vegetable omelet, quiche, bagels and lox, soup and muffins, and salmon, tuna or egg salad are all good choices. And don't forget to re-hydrate with plenty of water, juice or tea.