L-Carnitine Supplementation Combined with Aerobic Training Does Not Promote Weight Loss in Moderately Obese Women

Abstract

L-Carnitine (L-C) transports fatty acids into mitochondria for oxidation and is marketed as a weight loss supplement. In a double-blind investigation to test the weight loss efficacy of L-C, 36 moderately overweight premenopausal women were pair matched on Body Mass Index (BMI) and randomly assigned to two groups (N = 18). For 8 weeks the L-C group ingested 2 g twice daily of L-C, while the placebo (P) group ingested the same amount of lactose. All subjects walked for 30 min (60-70% maximum heart rate) 4 days/week. Body composition, resting energy expenditure (REE) and substrate utilization were estimated before and after treatment. For the subjects who completed the study (15 P, 13 L-C), no significant changes in mean total body mass (TBM), fat mass FM, and resting lipid utilization occurred over time, nor were there any significant differences between groups for any variable. Conversely REE increased significantly for all subjects, but no between group differences existed. Five of the L-C group experienced nausea or diarrhea and consequently did not complete the study. Eight weeks of L-C ingestion and walking did not significantly alter the TBM or FM of overweight women, thereby casting doubt on the efficacy of L-C supplementation for weight loss.

Acetyl-l-carnitine supplementation restores decreased tissue carnitine levels and impaired lipid metabolism in aged rats

“…by guest, on May 12, 2018 www.jlr.org Downloaded from liver were increased in aged rats. In the extrahepatic tissues, such as heart, skeletal muscle, and cerebral cortex, carnitine levels in aged rats were significantly decreased compared with those in young rats.…”

“…Brandsch and Eder (51) reported that l-carnitine did not show a positive effect on body weight reduction and body composition among rats fed an energy-deficient diet. Eight weeks of l-carnitine supplementation to moderately overweight premenopausal women did not alter the body weight or fat mass (52). The subjects in these studies were in adult stage and not in senescent stage, so they would have sufficient capacities for carnitine synthesis and transport to ensure competent fatty acid oxidation and lipid metabolism.…”

A suplementação de L-carnitina não promove alterações na taxa metabólica de repouso e na utilização dos substratos energéticos em indivíduos ativos

“…(19), com o objetivo de avaliar o aumento da oxidação de ácidos graxos em repouso, tenha encontrado resultados positivos com doses semelhantes à do presente estudo (aproximadamente 2 gramas/dia), outros, utilizando infusão intravenosa de carnitina (3 g) (17), doses inferiores e semelhantes (20)(21)(22), ou doses superiores (4 a 6 g/dia), não confirmaram tais achados (23)(24).…”

“…(24), seria a presença de concentrações normais musculares de carnitina nos indivíduos participantes. Em ambos os estudos, foram excluídos indivíduos vegetarianos, pois se sabe que a carnitina, além de seus precursores lisina e metionina, está presente em maiores quantidades nos alimentos de origem animal.…”

Efeitos ergogênicos da L-carnitina no metabolismo lipídico

“…Também não foram relacionadas às diferenças metabólicas e bioquímicas (gasto de energia em repouso, QR e ácidos graxos livres) entre os momentos antes e após a suplementação (COELHO et al 2005;COELHO, et al 2010). Da mesma forma, não foram observadas alterações significativas no peso e composição corporal de mulheres na pré-menopausa (19 a 48 anos) com excesso de gordura corporal (média de 35,2%), com a suplementação de L-carnitinia (4g/dia) e realização de exercícios físicos de intensidade moderada, durante um período de 8 semanas (VILLANI, et al 2000).…”