Effects of oral L-Carnitine supplementation on insulin sensitivity indices in response to glucose feeding in lean and overweight/obese males

Abstract

Infusion of carnitine has been observed to increase non-oxidative glucose disposal in several studies but the effect of oral carnitine on glucose disposal in non-diabetic lean vs. overweight/obese humans has not been examined. This study examined the effects of 14 days L-Carnitine L-Tartrate oral supplementation (LC) on blood glucose, insulin, NEFA and GLP-1 responses to an oral glucose tolerance test (OGTT). Sixteen male participants were recruited (lean (n=8) and overweight/obese (n=8)). After completing a submaximal predictive exercise test, participants were asked to attend three experimental sessions. These three visits were conducted, in the morning to obtain fasting blood samples and to conduct 2hr OGTT’s. The first visit was a familiarisation trial and the final two visits were conducted two weeks apart following 14 days of ingestion of placebo (PL, 3g glucose/day) then LC (3g LC/day) ingested as 2 capsules 3x/day with meals. On each visit blood was drawn at rest, at intervals during the OGTT for analysis of glucose, insulin, non-esterified fatty acids (NEFA) and total glucagon-like peptide-1 (GLP-1). Data obtained were used for determination of usual insulin sensitivity indices (HOMA-IR, AUC glucose, AUC insulin, 1st phase and 2nd phase β-cell function, estimated insulin sensitivity index, and estimated metabolic clearance rate). Data were analysed using RMANOVA and post-hoc comparisons where appropriate. There was a significant difference between groups for body mass, % fat and BMI with no significant difference in age and height. Mean (SEM) plasma glucose concentration at 30 minutes was significantly lower (p