Maintaining hyperinsulinaemia (150mU·L^-1) during steady-state hypercarnitinaemia (550µmol·L^-1) increases skeletal muscle total carnitine (TC) content by 15% within 5h. The present study aimed to investigate whether an increase in whole-body carnitine retention can be achieved through L-carnitine feeding in conjunction with a dietary-induced elevation in circulating insulin. On two randomized visits (Study A), 8 men ingested 3g·d^-1 L-carnitine followed by 4 x 500mL solutions, each containing flavored water (CON) or 94g simple sugars (glucose syrup; CHO). In addition, 14 men ingested 3g·d^-1 L-carnitine followed by 2 x 500mL of either CON or CHO for 2 weeks (Study B). Carbohydrate ingestion in Study A resulted in a 4-fold greater serum insulin AUC when compared with the CON (P<0.001), and lower plasma TC concentration throughout the CHO visit (P<0.05). Twenty-four h urinary TC excretion in the CHO visit was lower than the CON visit in Study A (155.0 ± 10.7 vs. 212.1 ± 17.2mg, respectively; P<0.05). In Study B, daily urinary TC excretion increased after 3d (65.9 ± 18.0 to 281.0 ± 35.0mg; P<0.001) and remained elevated throughout the CON trial. During the CHO trial, daily urinary TC excretion increased from a similar basal value of 53.8 ± 9.2 to 166.8 ± 17.3mg after 3d (P<0.01), which was less than during the CON trial (P<0.01) and remained lower over the course of the study (P<0.001). The difference in plasma TC concentration in Study A and 24h urinary TC excretion in both studies suggests insulin augmented the retention of carnitine in the CHO trials.