The Absorption of Soluble, Volatile Fatty Acids*

Experimental investigations show clearly that the absorption and metabolism of the short chain, water-soluble fatty acids differ in some way from those of the long chain fatty acids insoluble in water. Experiments by Lebedeff (1883), Leube (1895), Zunts (1901), and Eckstein (1929) show no evidence of the butyryl radical in the deposited fat when fed either as a fat or in the form of tributyrin. Davis (1930) found the butyryl radical present in the body fat if tributyrin was injected subcutaneously. Powell (1932) showed that fatty acids containing 8 carbon atoms arc not deposited in the animal when fed as glycerides, while fatty acids of 10 or more carbon atoms fed under the same conditions are deposited. None, so far, has suggested any satisfactory explanation for this difference in absorption. One possible explanation may be the difference in the mode of absorption of lipids and non-lipids, the non-lipids being water-soluble are absorbed by the intestinal capillaries and carried by the portal blood, while the lipids are absorbed by the lacteals and enter the blood by way of the thoracic duct. This is true of the watersoluble acetic acid which is known to be absorbed by the blood. Since butyric, caproic, and caprylic acids are all relatively soluble in water, it is quite possible that they might follow the path of absorption of non-lipids and might thus escape the glyceride synthesis. If this be true, these water-soluble fatty acids should not be found as glycerides in the lymph. It was to test the validity of this assumption that the following investigation was undertaken.