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.
There is some difference of opinion as to what extent fat may aid or retard the process of digestion, but it is a matter of very common experience that those persons whose digestive organs are feeble do not tolerate fats or oils well when eaten with other forms of food. This is no doubt owing to the fact that fats are practically unaltered in the mouth and stomach, and in the latter, when melted, they coat the mucous membrane and surround the particles of food with a thin film which materially interferes with the normal action of the gastric juice. For this reason fats are to be avoided by dyspeptics, and the fats selected for special nutritive processes should be in the form of good butter, cream, or cod-liver oil. On the other hand, fats may sometimes aid the digestibility of starchy foods by preventing them from forming lumpy masses in the mouth and stomach. For example, a well-roasted mealy potato may be made all the more digestible for an invalid by being mashed with a little butter or cream. The digestibility of fats may be much enhanced by the process of emulsification - i. e., of securing an extremely fine subdivision of the oil globules.
More than fifty years ago Horace Dobell, of London, emulsified beef fat and lard by means of pancreatic juice, and recently John F. Russell, of New York, has modified and extended the principle so as to emulsify all fats, fluid or solid, deriving products of permanent fine emulsion, capable of dilution with hot water, and possessing high nutritive value. These emulsions consist of one half fat, which is predigested and easily assimilated.
It is stated by Ringer that fats taken fasting lessen the secretion of bile, whereas if taken with or after food they increase it, but, as many kinds of food promote the secretion independently of fat, it is doubtful whether the latter possesses any very decided action in relation to bile formation.
Most of the fat used as food melts at the temperature of the body, which facilitates its digestion.
Children often eat butter more readily than any other form of fat.
As a rule, the stomach is less disturbed by animal than by vegetable fats taken in excess, and the former may be tolerated for a longer time. The limit of digestibility of increasing quantities of food is much sooner reached with fats than with other articles of diet, and they produce satiety early in a meal, but, as in the case of many foods, toleration may be acquired for the ingestion of fat, which is exemplified in the fact that many persons who cannot digest cod-liver oil completely at first may do so after two or three weeks' trial. This is, in part, due also to the general improvement in health which follows in some cases the administration of easily digested fat. Overdoses of fat at any time are apt to give rise to the formation of irritating acids which cause nausea and vomiting, with possibly abdominal cramps and loose evacuations. Fat taken too liberally with other food ceases to be economical for the system and becomes positively harmful.
Since fat is exclusively digested in the small intestine, diseases of any part of the alimentary canal are contraindications for its use.
Liquefied fats and oils are usually administered as a matter of routine when corrosive poisons have been swallowed, with the idea that they coat over the mucous membrane of the stomach and oesophagus and protect them from the action of the irritant. This protective action is overestimated, for it is difficult to coat to a sufficient degree a mucous membrane which is already moistened with watery mucus.
The digestibility of all fat depends somewhat upon its cooked state. Many persons are nauseated or made dyspeptic by eating hot mutton fat who can eat the same with impunity when it is cold. In the latter condition it becomes more friable, and, if thoroughly mixed in chewing with starchy food, or used as suet in the form of a farinaceous pudding, it becomes very much more digestible. Children usually dislike fat meat, but they are quite willing to take suet puddings, which, if light and well cooked, are wholesome.
While the various fats and oils, in general, have the same beneficial effect upon nutrition, there is considerable difference in their force value and in the facility with which one variety or another may be assimilated in individual cases. The animal fats have a higher nutritive power than those derived from vegetables, and liver fat, butter and cream, are the most serviceable of all.