Glucogenic and ketogenic capacities of lard, safflower oil, and triumdecanoin in fasting rats.

The glucogenic and ketogenic capicities of lard, safflower oil, and triundecanoin were compared. Rats were fed diets containing 30 percent of either lard (a ketogenic fat), triundercanoin (a glucogenic fat), or safflower oil (a fat high in linoleic acid). After 61 days, the rats were fasted for 72 hours. Plasma glucose and ketone body concentrations and carcass fatty acid loss were measured during fasting. The lard-fed animals, which lost mostly saturated even-chain length fatty acids during fasting, did not maintain their prefasting plasma glucose levels and became ketotic. The animals that had been fed triundecanoin (which mobilized considerable odd-chain fatty acid) maintained their prefasting plasma glucose levels and did not become ketotic. The animals fed safflower oil (which mobilized massive amounts of linoleic acid) showed even lower levels of plasma glucose and higher levels of ketone bodies than did the animals fed lard. This failure of safflower oil to avert fasting hypoglycemia suggests that linoleic acid is oxidized in a manner more like the saturated fatty acid of lard than like the glucogenic odd-chain fatty acid (undecanoic).