Medium-chain triglycerides (MCTs, C6–C12 fatty acids) exhibit rapid absorption, preferential portal transport, efficient mitochondrial β-oxidation, promoting acetyl-CoA formation and ketogenesis. Under high lipid flux or impaired β-oxidation, MCTs undergo ω-oxidation, producing dicarboxylic acids further metabolized peroxisomally, preventing fatty acid accumulation. Industrially, MCTs are synthesized via chemical or enzymatic esterification of caprylic (C8) and capric (C10) acids, yielding high-purity triglycerides used in food and medical nutrition. In Germany and across the European Union, they are primarily used in Foods for Special Medical Purposes (FSMPs) for conditions such as fat malabsorption, ketogenic dietary therapy for refractory epilepsy, and inherited disorders of long-chain fatty-acid oxidation. In Japan, MCTs are additionally incorporated into functional food systems, including Foods for Specified Health Uses (FOSHU) and Foods with Function Claims (FFC), targeting generally healthy adults and older populations. In the United States, MCTs are widely marketed as food ingredients, dietary supplements, clinical nutrition products, and medical foods, reflecting their status as generally recognized as safe (GRAS). This review integrates knowledge on MCT metabolism, industrial production, clinical applications, and regulatory frameworks in Germany, Japan, and the United States, highlighting how regulatory environments influence the translation of MCTs from clinical nutrition toward broader preventive health strategies.

Background: In Japan, many individuals experience symptoms of constipation. Medium-chain triglycerides (MCTs), composed solely of medium-chain fatty acids, have been suggested to improve bowel movements in athletes. However, most prior studies have assumed high-dose intake for ergogenic purposes, and evidence on the effects of low-dose interventions in generally healthy Japanese adults with a tendency toward constipation remains limited. In this study, we investigated the effects of consuming a small amount of MCTs on bowel movements, subjective abdominal condition, and health-related quality of life (HRQOL) in Japanese adults prone to constipation. Methods: This randomized, double-blind, long-chain triglyceride (LCT)-controlled, crossover trial with a 2-week washout enrolled 88 healthy Japanese adults aged 20–64 years with three to five bowel movements per week. Participants ingested 2 g/day of MCTs and 2 g/day of LCTs for 2 weeks each. Bowel movement indicators, subjective abdominal condition, and HRQOL were measured. Results: Using a statistical model for within-participant comparisons, significant diet effects were observed for the number of days with bowel movements, bowel movement frequency, and stool volume. A post-hoc analysis further confirmed that the change from baseline in the number of days with bowel movements at week 2 was significantly greater during the MCT intake period than during the LCT intake period. By contrast, although multiple questionnaire-based endpoints showed significant pre–post changes within intervention periods, the corresponding between-diet differences were not clearly demonstrated. Conclusion: Daily intake of even a small amount of MCTs, compared with LCTs, may be helpful in improving bowel movements in Japanese adults prone to constipation. Clinical trial registration: https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000060455 ; identifier UMIN000052997.