Carnitine and Energy Mobilization

Stephens et al. (2013) reported new data from a randomized controlled trial by Wall et al. (2011).  In this trial, there were seven participants each in the intervention and in the placebo.  They were all moderately trained recreational athletes.  Both groups drank a beverage containing 80 g of carbohydrate twice a day, in the morning and again four hours later.  The intervention group’s drink also contained 2 g of l-carnitine l-tartrate.  This went on for 24 weeks; however, the results reported by Stephens et al. (2013) were from 12 of the participants at 12 weeks.  Both studies reported a 20% increase in total carnitine in the intervention group.  Wall et al. (2011) reported in their results section that the intervention group had gained 2.4 kg of body mass at 12 weeks, however they did not comment on this in the discussion.  In contrast, the Stephens et al. (2013) report emphasized this result, pointing out that the control group had increased body mass by 1.9 kg and fat mass by 1.8 kg (18%) over 12 weeks compared to zero in the intervention, and they went on to discuss some of the possible mechanisms behind why these gains did not happen in the intervention group.  They reported, with a p value less than 0.05, that the intervention group saw a 200% increase in long-chain acyl-CoA, and a 6% increase in energy expenditure, whereas the placebo group did not see any changes in these three measures.  They also noted changes in gene expression in the intervention group.  They suggest that the upregulated genes are contributing to an ability to increase fat metabolism and energy expenditure while preventing the adverse changes in body composition associated with carbohydrate overfeeding.

References:

Stephens, F. B., Wall, B. T., Marimuthu, K., Shannon, C. E., Constantin-Teodosiu, D., Macdonald, I. A., & Greenhaff, P. L. (2013). Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. The Journal of Physiology, 591(18), 4655–4666. 

Wall, B. T., Stephens, F. B., Constantin-Teodosiu, D., Marimuthu, K., Macdonald, I. A., & Greenhaff, P. L. (2011). Chronic oral ingestion of l-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. (2011).  Journal of Physiology, 589(4), 963–973.