This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
In Germany fruit soups are more in vogue for general use than in this country, and they are often prescribed in fevers when diarrhoea does not exist. Uffelmann directs that for making a fruit soup one part of fruit to four or five of water may be used, and Bauer recommends soups "made by boiling fresh or dried fruits with water, with or without the addition of sugar, lemon peel, etc., and freed from the solid residue by pressure".
Dried Fruits can be eaten less abundantly than fresh fruits. Some of the dried fruits are wholly indigestible; such are currants and citrons. Others, like figs or prunes, are wholesome, and raisins, sultanas, dates, etc., contain considerable nourishment. All these dried fruits are preserved in their own sugar (glucose), which forms a sticky, gummy, non-crystallised mass. Dried apples, peaches, prunelles, etc., are preserved simply by the evaporation of the excess of water which they contain.
Dried "currants" are the berries of a vine cultivated in the Ionian Islands. The word currant is a corruption of Corinth. The fruit in its dried state is wholly indigestible.
When dried fruits, such as figs or dates, have become too hard they may be softened and made more palatable by pouring boiling water over them and allowing them to soak for a few hours, or the fruit may be put into cold milk and brought to the boiling point over the fire. This method will soften them in a quarter of an hour.
A simple fruit diet which has been advocated for the cure of obesity and other ailments is the following: Three meals a day are eaten, consisting of half a pint to a pint of milk, with from two to six ounces of whole-meal bread and a similar quantity of figs or dates, prepared in milk as above described. Obviously this diet is not sufficiently sustaining to be long endured.
Among the commoner fruits of easy digestion are grapes, oranges, grape fruit, lemons, cooked apples, figs, peaches, strawberries, and raspberries.
Somewhat less digestible are melons, prunes, raw apples, pears, apricots, bananas, and fresh currants.
Of course the digestibility depends very much upon ripeness and freshness of the fruit as well as personal idiosyncrasy, and any classification can only be approximate.
The most useful fruits for the sick are lemons, oranges, baked apples, stewed prunes, grapes, banana meal (not the fruit pulp).