Medium-chain triglycerides improve lipid metabolism in obese rats through increasing the browning of adipose tissue via sympathetic regulation.

This study aimed to determine the effect and mechanism of medium-chain triglycerides (MCTs) on promoting the browning of adipose tissue. A high-fat diet was fed to the Sprague-Dawley rats to induce obesity, then caprylic triglycerides (CYTs), capric triglycerides (CTs) and lauric triglycerides (LTs) were used to treat the obese rats for 12 weeks. The obesity phenotype and molecular changes related to browning were determined. The results showed that all three MCTs promoted the browning/beiging of the adipose tissues (brown and white adipose tissue), and lipolysis in these tissues was also increased, which ameliorated high-fat diet-induced lipid metabolic disorders in the obese rats. The LT group showed the highest expression levels of lipolysis- and browning/beiging-related proteins, followed by the CT group and CYT group. We speculate that the browning process may be related to sympathetic regulation and all the three MCT administration increased the secretion of neurotrophic factors both in the hypothalamus and adipose tissue. Then, intra-adipose sympathetic arborization increased, resulting in the activation of the sympathetic regulatory system in MCT groups, and the LT group also showed the highest sympathetic nerve fiber density, followed by the CT group and CYT group. We have for the first time found that the effect of medium-chain fatty acids on adipose tissue browning might be related to the types of fatty acids.