Digestive speed and efficiency vary with individuals and with circumstances. However, in general, foods leave the average stomach about as follows:–fruits, vegetables, bread, eggs, lamb, beef, pork, chicken, nuts, guinea hen. Carbohydrates usually leave the stomach rapidly, proteins remain longer. Foods requiring longer time for gastric digestion are not necessarily harder to digest; it is often merely that the process of digestion is different.
Foods requiring longer time to digest remain in the stomach longest. Beef requires but slightly longer to digest than lamb. Chicken requires longer than pork despite all of the fat of the latter.
Red beets pass through the stomach rapidly. So do asparagus, raw tomatoes, lettuce (unless delayed by the usual dressings), and most vegetables low in protein and starch. Vegetables containing much starch are held up for more thorough digestion. Low protein vegetables leave the stomach with little change. Raw cabbage leaves the stomach more quickly than cooked cabbage, a thing most people know. Baked beans are slow to leave the stomach. Spinach is slow, compared with other vegetables.
Eggs and milk go more slowly than eggs alone. Old eggs require more time in the stomach than fresh, or even cold storage eggs. Boiled eggs remain in the stomach longer than raw ones. Scrambled eggs remain longer still. Raw egg whites leave the stomach rapidly. Egg white does not encourage gastric secretion, unless taken with orange juice, and is poorly digested and badly assimilated.
Raw milk leaves the stomach slowly. Pasteurized milk more slowly and boiled milk still more slowly. Milk rich in fat leaves the stomach more slowly than milk low in fat content. Buttermilk stimulates gastric secretion.
Bacon digests slowly and, perhaps due to its fat, lowers stomach acidity. It is difficult for most people to digest. Fat markedly inhibits gastric secretion and the movements of the stomach and slows down digestion.
Foods are not digested when they have passed out of the stomach. A large part of the work of digestion takes place in the intestine.
We learned in the previous chapter that such things as coffee, tea, bitters, etc., cause an early emptying of the stomach without, in any way, shortening their digestion time. In other words, foods may be sent out of the stomach before gastric digestion is complete.