Majid Koozehchian, MS
L-Carnitine and Weight Loss:
L-carnitine (CARN) is a trimethylamine molecule being synthesized in mammals from essential amino acids lysine and methionine in the kidney, liver, and brain or ingested through diet. CARN is a cofactor of carnitine palmitoyl transferase and serves as a transporter of long-chain fatty acids such as triglycerides across the mitochondria for β-oxidation (1, 2); therefore, CARN supplementation may increase lipid metabolism and promotes a decrease in fat mass. CARN ingestion may influence plasma CARN concertation, stimulate weight loss in animals (3), and improve β-oxidation in adults (4). The rationale for CARN ingestion as a weight-loss agent is based on the assumption that elevated cellular levels of CARN could theoretically increase transport of fats into the mitochondria and thus provide more substrates for fat metabolism (5). This would stimulate elevated β-oxidation and gradual reduction of fat reserves; however, the use of CARN as a weight loss dietary supplement yields inconsistent results. The results of some studies indicated that oral CARN ingestion does not stimulate weight loss in overweight or trained subjects (6-8). This is not in line with clinical studies finding the beneficial role of supplementary CARN in the management of obese individuals (9). It has been indicated that inhibition of hypothalamic carnitine palmitoyltransferase-1 decreases food intake (10). Dietary CARN stimulates function and transcriptional rate of carnitine palmitoyltransferanse (11), which explains a stimulation of appetite by CARN supplementation. Consequently, claims that CARN supplementation promotes weight loss in humans are not sufficiently evidenced and need to be investigated in more detail.
L-Carnitine and Recovery from Exercise:
CARN is important for normal muscle bioenergetics for at least three reactions: CARN transports required fatty acid for β-oxidation; it assists in regulation of the mitochondrial acyl-Co A / CoA ratio, and stabilization of cell membranes; and it assists in detoxification of potentially toxic metabolites, and stabilization of cell membranes (12). The ideal performance of metabolic processes is essential during severe exercise. Hypothetically, CARN availability may be the limiting factor for β-oxidation or the removal of acyl-CoA during exercise. If this is true, CARN supplementation in healthy individuals should improve exercise performance. The ergogenic benefits of CARN for endurance exercise is based on three assumptions. The first hypothesis mentions that the existing CARN concentration in muscles would be too low to allow carnitine acyltransferases to function at a high rate and to support the elevated rate of fat oxidation during exercise. Second, oral ingestion of CARN should increase total muscle CARN concentration. Third, this increase in muscle CARN should elevate rate of oxidation of intramuscular fatty
acids during exercise, thereby reducing muscle glycogen depletion and delaying fatigue (13). During severe exercise, the free CARN concentration in muscle will decrease because the compound reacts with acetyl-CoA. During severe exercise, the free CARN concentration may drop to very low levels, which is a possible mechanism for the reduction of plasma fatty acid and intramuscular triacylglycerol oxidation during severe exercise (14).
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