Changes in Tissue Lipids in Response to Diet

Abstract

Changes in the fatty acid composition of three selected adipose tissues (subcutaneous, mesenteric and interscapular fat) of rats in response to changes of the dietary fat were determined. Safflower oil, containing about 75% of linoleic acid, and conconut oil, furnishing some 68% of lauric and myristic and less than 3% of linoleic acids, were fed as 10% of adequate semisynthetic diets. Three groups of rats were compared: those fed coconut oil from weaning age, those fed safflower oil after an initial three-week period of coconut oil, and those changed back to coconut oil after a period of safflower oil feeding. Groups of animals were killed, and the tissues were analyzed at intervals of one, three, 6 and 9 weeks after change of diet. Changes in the dietary fat produced changes in the composition of the adipose tissue within one week or less. Most changes observed were in the direction that might have been predicted from the composition of the dietary fat. Some variations from this pattern were evidently due to variations in age, sex and growth rate of the experimental animals. Generally, the changes were qualitatively similar in all three tissues observed. The interscapular fat had higher levels of nitrogen and lower levels of fatty acids than did the other two tissues, and its fat content varied less. Equilibration of the composition of the adipose tissue with that of the dietary fat occurred earlier in female rats than in males. Of the three tissue fats, the interscapular reached an equilibrium level earliest, followed by mesenteric and finally by subcutaneous fat. The half-time of replacement for linoleic acid ranged from 11 to 53 days, depending on the sex of the animals and the tissue in question. Lauric and myristic acids had shorter half-times of replacement and were accumulated in lower proportions in relation to their intake. The most striking difference between male and female rats was a decrease in the total fatty acid content, which occurred only in females at 10 to 14 weeks of age. The decrease was accompanied by an increase in water content. Since the observed ratio of unsaturated to saturated fatty acids was not constant, it is possible that the animal tends instead to maintain adipose tissue of constant physical properties. The data support the hypothesis that the rat can store dietary linoleic acid in its adipose tissue during a period of high intake for slow release when the dietary supply is low.