Endogenous synthesis cannot compensate for absence of dietary oleic acid in rats

It is important to know whether an organism is able to synthesize all the oleic acid it needs. To determine this, it is sufficient to feed animals a diet containing essential fatty acids but totally lacking oleic acid, and then determine whether tissue concentrations of fatty acids of the (n-9) series are altered due to insufficient endogenous synthesis of oleic acid from stearic acid. In fact, the effects of a total oleic acid deficiency have not previously been studied because all the vegetable oils used in human and animal nutrition contain this fatty acid in variable amounts. Thus, we fed rats semipurified diets whose lipids (triglycerides) were synthesized chemically. Female rats were fed the diets for 3 wk before mating, and their pups (fed the same diets) were killed when 21 and 60 d old. Generally speaking, oleic acid deficiency resulted in a lower level of this acid in the various organs examined (liver, kidney, testes, heart, muscle and sciatic nerve in 21-d-old rats and liver, kidney, heart, muscle and sciatic nerve in 60-d-old rats). Brain, myelin and nerve endings were not affected at either age. This lower level was accompanied by a higher level of 16:1(n-7) and, to a lesser extent, 18:1(n-7). Dietary supplementation with oleic acid (1666 mg/100 g diet) for up to 21 d resulted in normal levels of this fatty acid in some organs (liver, heart, sciatic nerve) but not in others (kidney, muscle, testes) and a decrease in 16:1(n-7), which returned to about the same levels as in the control group in all organs except liver. Adding small or large amounts of stearic acid to the oleic acid-deficient diet had little or no effect on oleic acid levels in the tissues. We conclude that rats (particularly in liver) do not have sufficient synthesizing potential to guarantee the normal fatty acid composition of certain organs if oleic acid is totally absent in the diet.