Carbohydrate ingestion augmentsl-carnitine retention in humans

Abstract

Maintaining hyperinsulinemia (∼150 mU/l) during steady-state hypercarnitinemia (∼550 μmol/l) increases skeletal muscle total carnitine (TC) content by ∼15% within 5 h. 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), eight men ingested 3 g/day l-carnitine followed by 4 × 500-ml solutions, each containing flavored water (Con) or 94 g simple sugars (glucose syrup; CHO). In addition, 14 men ingested 3 g/day l-carnitine followed by 2 × 500 ml of either Con or CHO for 2 wk ( study B). Carbohydrate ingestion in study A resulted in a fourfold greater serum insulin area under the curve when compared with Con ( P < 0.001) and in a lower plasma TC concentration throughout the CHO visit ( P < 0.05). Twenty-four-hour urinary TC excretion in the CHO visit was lower than in the Con visit in study A (155.0 ± 10.7 vs. 212.1 ± 17.2 mg; P < 0.05). In study B, daily urinary TC excretion increased after 3 days (65.9 ± 18.0 to 281.0 ± 35.0 mg; 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 ± 17.3 mg after 3 days ( P < 0.01), which was less than during the Con trial ( P < 0.01), and it remained lower over the course of the study (P < 0.001). The difference in plasma TC concentration in study A and 24-h urinary TC excretion in both studies suggests that insulin augmented the retention of carnitine in the CHO trials.