Effect of a Lard, Soybean-oil and Fish-oil Diet during the Growth Period on Preferential Fish-oil Diet Intake by Rats in Later Life

Abstract

We previously reported that fish oil is nutritionally less desirable than lard and soybean oil. In the present study, to investigate the reasons for this, three groups of 4-week-old male Fischer 344 rats were fed one of three diets: a lard diet, a soybean-oil diet or a fish-oil diet (experimental period). After 8 weeks, all rats were placed on a self-select regimen and allowed to choose a lard diet or a fish-oil diet for 3 weeks (self-selection period). After the experimental period, plasma lipid concentrations were lower in the fish-oil diet group than in the other two groups. At the beginning of the self-selection period, the ratio of the fish-oil diet intake [fish-oil diet intake (g) /total intake (g)] was highest in rats fed the lard diet and lowest in rats fed the fish-oil diet. However, the ratio in rats fed the lard diet and the soybean-oil diet decreased, and that in rats fed the fish-oil diet increased gradually, so that by the 7-9th day of the self-selection period no significant difference in the ratio was evident among these three groups. After the self-selection period, no significant difference in the plasma lipid concentration was observed among these three groups. Therefore, these 3 groups of rats counteracted the shortage of fatty acids at the beginning of the self-selection period and then self-selected the lard diet and the fish-oil diet to maintain n-6/n-3=3. These findings suggest that rats have an ability to consume a lard diet and a fish-oil diet to obtain an adequate ratio of essential fatty acids.