Dietary combination of sucrose and linoleic acid synergistically accumulates the intramuscular lipid and decreases the muscle strength in Zucker diabetic fatty rats

Background and objectives: We have previously found that the dietary combination of sucrose and linoleic acid synergistically induces glucose and lipid metabolism abnormalities, endoplasmic reticulum stress, and inflammatory responses in the skeletal muscle of rats with obesity. We hypothesized that such interactions in skeletal muscle may also affect muscle function. In the present study, we examined the effects of the dietary combinations of carbohydrates and lipids on muscle mass and motor function. Methods: Five-week-old, female Zucker diabetic fatty rats were fed experimental diets (PO, PL, SO, SL) combining palatinose (P) or sucrose (S) and oleic acid (O) or linoleic acid (L) as major carbohydrate and lipid sources, respectively, for 12 weeks. The motor functions were measured by handgrip and treadmill test. Results: The SL group showed the synergistic decrease in grip strength compared with the other groups, but there were no differences in muscle weight or mRNA expression of MuRF-1 and Atrogin-1. Interestingly, intramuscular neutral lipids accumulation in the extensor digitorum longus (EDL) muscle, a fast-twitch muscle, was significantly increased in the SL group. Furthermore, a negative correlation was observed between the amount of intramuscular lipid in the EDL muscle and grip strength, suggesting that the SL diet promotes intramuscular lipid accumulation as well as the loss of muscle strength. We examined the expression of genes involved in intracellular uptake and accumulation of lipids and found that they were elevated not only in the SL group but also in the PL group. On the other hand, the expression of genes involved in lipolysis and fatty acid oxidation was not elevated in the SL group, but only in the PL group. Conclusions: It can be considered that simultaneous ingestion of sucrose and linoleic acid would result in relatively higher lipid synthesis in the EDL muscle, which leads to intramuscular lipid accumulation and that could decrease muscle strength. It was suggested that the dietary combinations of carbohydrates and lipids may contribute to muscle function by differentially affecting lipid metabolism and intramuscular lipid accumulation in obesity.