Trafficking of dietary oleic, linolenic, and stearic acids in fasted or fed lean rats

Abstract

Increasing evidence supports the notion that there are significant differences in the health effects of diets enriched in saturated, as opposed to monounsaturated or polyunsaturated fat. However, the current understanding of how these types of fat differ in their handling by relevant tissues is incomplete. To examine the effects of fat type and nutritional status on the metabolic fate of dietary fat, we administered (14)C-labeled oleic, linolenic, or stearic acid with a small liquid meal to male Sprague-Dawley rats previously fasted for 15 h (fasted) or previously fed ad libitum (fed). (14)CO(2) production was measured for 8 h after tracer administration. The (14)C content of gastrointestinal tract, serum, liver, skeletal muscle (soleus, lateral, and medial gastrocnemius), and adipose tissue (omental, retroperitoneal, and epididymal) was measured at six time points (2, 4, 8, 24, and 48 h and 10 days) after tracer administration. Plasma levels of glucose, insulin, and triglyceride were also measured. Oxidation of stearic acid was significantly less than that of either linolenic or oleic acid in both the fed and fasted states. This reduction was in part explained by a greater retention of stearic acid within skeletal muscle and liver. Oxidation of oleate and stearate were significantly lower in the fed state than in the fasted state. In the fasted state, liver and skeletal muscle were quantitatively more important than adipose tissue in the uptake of dietary fat tracers during the immediate postprandial period. In contrast, adipose tissue was quantitatively more important than skeletal muscle or liver in the fed state. The movement of carbons derived from dietary fat between tissues is a complex time-dependent process, which varies in response to the type of fat ingested and the metabolic state of the organism.

Triglyceride Synthesis in Epididymal Adipose Tissue

“…1). The latter was independent of dietary fat composition and further supports observations regarding bias when using one labeled fatty acid to trace the fate of other fatty acids (27,28). The 2 H labeling of triglyceride palmitate was consistent with the generally accepted hypothesis that dietary carbohydrate provides an excellent substrate for de novo lipogenesis (Fig.…”

Prior Exercise Increases Dietary Oleate, but Not Palmitate Oxidation

“…We compared the effects of rest, light intensity exercise, moderate intensity exercise, and heavy exercise on the oxidation of dietary fat given in a meal after the completion of exercise and tested whether this associated with body fatness. Monounsaturated, [1-13 C]oleate, and saturated, [d 31 ]palmitate, fatty acids were used because they represent the most common fatty acids in the average U.S. diet (16) and because Bessesen et al have demonstrated that the degree of saturation is important in the organ distribution of dietary fats (17). Previous studies have shown differential oxidation of dietary fatty acids based on chain length and degree of saturation (18).…”

Sustained increase in dietary oleic acid oxidation following morning exercise

“…36 Although we could not identify a mechanism at this time to explain the increased partitioning of dietary oleate to oxidation after exercise, the findings of the current study and our previous studies 5,6 do suggest that at least some of the protective effect of exercise on weight control may be due to the altered trafficking. 37 The results indicate that the level of exercise is not as important as the volume of exercise, as long as a difference in energy balance can be maintained over the long term. In addition, our findings suggest that individuals attempting to control weight with exercise would benefit with the replacement of dietary saturated fats by monounsaturated fats.…”