In case of an excess of hydrochloric acid in the stomach, lemon juice or citrus fruits are valuable about half an hour before a meal, as when taken on an empty stomach they decrease the secretion of hydrochloric acid.
When the secretion of hydrochloric acid is limited, acids are given after a meal to supplement the deficiency, or stimulate the glands to activity.
Sweet or bland fruits are those containing a lesser percentage of acids. Among these are pears, raspberries, grapes, bananas, blackberries, blueberries, melons, and some peaches, apples, and plums.
Of this class of fruits, dates, figs, prunes, and grapes (raisins), furnish most nutriment, because, as will be noted by Table [III], these fruits contain a large amount of carbohydrates in the form of sugar.
The protein in these sweet fruits is largely in the seeds and, as the seeds are not digested, they have no real food value for the individual.
Figs and prunes, peaches, apples, and berries are laxative—probably the laxative action of figs and berries is due to the seeds, and of the others to the salts and acids they contain, and to the cellulose or fibrous material which furnishes bulk.
TABLE III
Fruits
| FOOD MATERIALS | Water per cent. | Protein per cent. | Ether Extract per cent. | Carbohydrates per cent. | Ash per cent. | Cellulose per cent. | Acids per cent. |
| Apples | 82.50 | 0.40 | 0.5 | 12.5 | 0.4 | 2.7 | 1.0 |
| Apricots | 85.00 | 1.10 | 0.6 | 12.4 | 0.5 | 3.1 | 1.0 |
| Peaches | 88.80 | 0.50 | 0.2 | 5.8 | 0.6 | 3.4 | 0.7 |
| Plums | 78.40 | 1.00 | 0.2 | 14.8 | 0.5 | 4.3 | 1.0 |
| Cherries | 84.00 | 0.80 | 0.8 | 10.0 | 0.6 | 3.8 | 1.0 |
| Gooseberries | 86.00 | 0.40 | 0.8 | 8.9 | 0.5 | 2.7 | 1.5 |
| Currants | 85.20 | 0.40 | 0.8 | 7.9 | 0.5 | 4.6 | 1.4 |
| Strawberries | 89.10 | 1.00 | 0.5 | 6.3 | 0.7 | 2.2 | 1.0 |
| Whortleberries | 76.30 | 0.70 | 3.0 | 5.8 | 0.4 | 12.2 | 1.6 |
| Cranberries | 86.50 | 0.50 | 0.7 | 3.9 | 0.2 | 6.2 | 2.2 |
| Oranges | 86.70 | 0.90 | 0.6 | 8.7 | 0.6 | 1.5 | 1.8 |
| Lemons | 89.3 | 1.00 | 0.9 | 8.3 | 0.5 | 1.5 | 1.8 |
| Pineapples | 89.3 | 0.04 | 0.3 | 9.7 | 0.3 | 1.5 | 7.0 |
| Pears | 83.90 | 0.40 | 0.6 | 11.5 | 0.4 | 3.1 | 0.1 |
| Blackberries | 88.90 | 0.90 | 2.1 | 2.3 | 0.6 | 5.2 | 1.6 |
| Raspberries | 84.40 | 1.00 | 2.1 | 5.2 | 0.6 | 7.4 | 1.4 |
| Mulberries | 84.70 | 0.30 | 0.7 | 11.4 | 0.6 | 0.9 | 1.8 |
| Grapes | 79.00 | 1.00 | 1.0 | 15.5 | 0.5 | 2.5 | 0.5 |
| Watermelons | 92.90 | 0.30 | 0.1 | 6.5 | 0.2 | 1.0 | 0.5 |
| Bananas | 74.00 | 1.50 | 0.7 | 22.9 | 0.9 | 0.2 | 0.5 |
| Dates, dried | 2.08 | 4.40 | 2.1 | 65.1 | 1.5 | 5.5 | 7.0 |
| Figs, dried | 2.00 | 5.50 | 0.9 | 62.8 | 2.3 | 7.3 | 1.2 |
| Prunes, dried | 2.64 | 2.40 | 0.8 | 66.2 | 1.5 | 7.3 | 2.7 |
| Raisins | 10.60 | 2.50 | 4.7 | 74.7 | 3.1 | 1.7 | 2.7 |
The astringent and acid taste of unripe fruits is due to the tannin and the acids. Oxygen is necessary to ripen fruits and the slow natural maturing of the fruit on the tree enables the oxygen to enter into combination with these substances, lessening their reaction and altering the starch into glucose or levulose.
Fruits ripened artificially lack this chemical action of sun and oxygen, hence the decreased palatability and digestibility of fruits so ripened. If underripe fruits are freely eaten they ferment in the alimentary tract and this fermentation causes the colic, vomiting, and diarrhea so often experienced. Overripe fruit, from the decomposition products which have already begun to form and which are further released in the stomach or bowels, may produce the same results.