Hi. According to Dr. Joel Fuhrman the body shuts down the production of digestive enzymes during a "lengthy" Water Fast
(one of about 2 weeks I guess). As such it is important that food be reintroduced slowly and incrementally. You can break a fast with juices but it's better to start off eating whole, juicy fruits. The fiber in the fruit encourages a bowel movement a little sooner. Watermelon
is ideal, but one can also start with orange slices. On the first day of eating have meals of about half an orange or an equivalent amount of Watermelon
every two hours. On the second day continue the fruit only diet with one medium-sized piece of fruit or melon every three hours. On the third day have 3 fruit only meals and a fourth meal consisting of lettuce. By the fourth day you can resume a three meals per day schedule but the size of your meals should be smaller than the usual prefast amount. At this time a small amount of cooked vegetables such as butternut squash or potato can also be added.
The protective layer of mucus in the stomach thins while fasting; therefore, certain foods should be avoided immediately after a fast to prevent stomach irritation and abdominal cramping. Pineapple and any other fermented food should be avoided. Under and overripe foods and dried herbs and spices can also irritate the digestive system. Dry foods such as baked potato, grains, and dried fruit should not be eaten to break a fast. It is important to eat high-water-content food at first for ease of digestion.
For those of you fasting for weight loss, know that because the body's metabolic rate is slower than normal for the first month after a fast it is better to stick to raw fruits and vegetables for the first month after a fast and small amounts of lightly steamed green vegetables. During this time eating cooked carbohydrates will greatly increase your chance of weight gain. One will definitely gain weight postfast regardless of whether this advice is followed; emphasizing a raw fruits and vegetables diet over cooked carbohydrates will minimize the amount of weight gained, though.
For those of you fasting to remedy irritable bowel disease, it is preferable to start with something gentle on the bowel, like a small, green zucchini, steamed until just soft to break a fast.
Nota Bene: the above information was taken from Fuhrman's "Fasting and Eating for Health"