Carbohydrate Foods.
The idea of starchy foods is usually connected with such substances as laundry starch, cornstarch, arrow root, etc. These are, of course, more concentrated forms of starch than potatoes, rice, etc. Many starchy foods contain other ingredients, and some are especially rich in proteids.
The following table may help to make this clear (Atwater):—
Percentage of Starch in Vegetable Foods.
| Per Cent. | |
| Wheat bread | 55.5 |
| Wheat flour | 75.6 |
| Graham flour | 71.8 |
| Rye flour | 78.7 |
| Buckwheat flour | 77.6 |
| Beans | 57.4 |
| Oatmeal | 68.1 |
| Cornmeal | 71.0 |
| Rice | 79.4 |
| Potatoes | 21.3 |
| Sweet Potatoes | 21.1 |
| Turnips | 6.9 |
| Carrots | 10.1 |
| Cabbage | 6.2 |
| Melons | 2.5 |
| Apples | 14.3 |
| Pears | 16.3 |
| Bananas | 23.3 |
It is estimated that starch composes one-half of peas, beans, wheat, oats and rye, three-fourths of corn and rice, one-fifth of potatoes. Vegetable proteids, as already stated, are less easily digested than those belonging to the animal kingdom, therefore it must be remembered that a purely vegetable diet, even though it may be so arranged as to provide the necessary protein, is apt to over-tax the digestive organs more than a mixed diet from both the animal and vegetable kingdoms. Much depends upon the cooking of the starchy foods in order to render them digestible. (Study chapter on Digestion in the Public School Physiology.)
STARCH.
The digestion of starch—which is insoluble in cold water—really begins with the cooking, which by softening the outer coating or fibre of the grains, causes them to swell and burst, thereby preparing them for the chemical change which is caused by the action of the saliva in converting the starch into a species of sugar before it enters the stomach. Substances which are insoluble in cold water cannot be absorbed into the blood, therefore are not of any value as food until they have become changed, and made soluble, which overtaxes the digestive organs and causes trouble. The temperature of the saliva is too low to dissolve the starch fibre unaided. Each of the digestive juices has its own work to do, and the saliva acts directly upon the starchy food; hence the importance of thoroughly masticating such food as bread, potatoes, rice, cereals, etc. The action of heat, in baking, which causes the vapor to rise, and forms the crust of starchy food, produces what is called dextrine, or partially digested starch. Dextrine is soluble in cold water, hence the ease with which crust and toast—when properly made—are digested. It is more important to thoroughly chew starchy food than meat, as it is mixed with another digestive juice, which acts upon it in the stomach.