Oral hydroxycitrate supplementation enhances glycogen synthesis in exercised human skeletal muscle

Abstract

Glycogen stored in skeletal muscle is the main fuel for endurance exercise. The present study examined the effects of oral hydroxycitrate (HCA) supplementation on post-meal glycogen synthesis in exercised human skeletal muscle. Eight healthy male volunteers (aged 22·0 (SE 0·3) years) completed a 60-min cycling exercise at 70-75 % _ VO 2 max and received HCA or placebo in a crossover design repeated after a 7 d washout period. They consumed 500 mg HCA or placebo with a high-carbohydrate meal (2 g carbohydrate/kg body weight, 80 % carbohydrate, 8 % fat, 12 % protein) for a 3-h post-exercise recovery. Muscle biopsy samples were obtained from vastus lateralis immediately and 3 h after the exercise. We found that HCA supplementation significantly lowered post-meal insulin response with similar glucose level compared to placebo. The rate of glycogen synthesis with the HCA meal was approximately onefold higher than that with the placebo meal. In contrast, GLUT4 protein level after HCA supplementation was significantly decreased below the placebo level, whereas expression of fatty acid translocase (FAT)/CD36 mRNA was significantly increased above the placebo level. Furthermore, HCA supplementation significantly increased energy reliance on fat oxidation, estimated by the gaseous exchange method. However, no differences were found in circulating NEFA and glycerol levels with the HCA meal compared with the placebo meal. The present study reports the first evidence that HCA supplementation enhanced glycogen synthesis rate in exercised human skeletal muscle and improved post-meal insulin sensitivity.Key words: Insulin resistance: Ergogenic aids: GLUT4: FAT/CD36: Hydroxycitrate Hydroxycitrate (HCA), a compound having a structure similar to citrate, is enriched in an Indian fruit known as Garcinia cambogia (1,2) , which is commonly used as a traditional Indian medicine. It is generally known that citrate is an allosteric regulator for a number of enzymes that are involved in carbohydrate and fat metabolism, such as phosphofructokinase, a key enzyme regulating glycolysis (3) , and acetyl Co-A carboxylase, a key enzyme regulating fatty acid synthesis (4) .HCA can also serve as a competitive inhibitor for ATP-citrate lyase (5) , which directs energy metabolism towards fatty acid oxidation. Therefore, administration of HCA is expected to cause metabolic ramification in vivo. The results of several mouse studies support the idea that oral HCA supplementation lowered plasma insulin concentration (6) , enhanced the whole-body fatty acid oxidation and spared muscle glycogen (7) . There is a paucity of information regarding the effects of HCA supplementation on fat metabolism in human subjects. Lim et al. (8) have previously reported that short-term HCA supplementation significantly lowered respiratory quotient (RQ) during exercise. Reduced RQ reflects energy reliance towards fat metabolism. In contrast, Kriketos et al. performed a double-blind, randomised, crossover study involving 3-d supplementation of HCA or placebo for ...

Effects of Taurine Administration on Carbohydrate Metabolism in Skeletal Muscle during the Post-Exercise Phase

“…Recent studies suggested that during the postexercise recovery, reducing carbohydrate utilization as a fuel effectively enhances skeletal muscle glycogen repletion. For example, oral administration of hydroxycitrate, which increases energy reliance on fat oxidation during the post-exercise phase, improved glycogen repletion in skeletal muscle (24). In contrast, accelerating carbohydrate oxidation by exposure to hot conditions impaired post-exercise glycogen resynthesis (25).…”

(-)-Hydroxycitric Acid Reduced Lipid Droplets Accumulation Via Decreasing Acetyl-Coa Supply and Accelerating Energy Metabolism in Cultured Primary Chicken Hepatocytes

“…Previous studies had reported that (-)-HCA increases weight loss [19, 20], promotes energy expenditure [21-23], increases the rate of glycogen synthesis [24] and suppresses de novo fatty acid synthesis [25-27]. Recently, our laboratory found that (-)-HCA treatment promoted protein synthesis and enhanced energy expenditure in male rats [28].…”

Oral conjugated linoleic acid supplementation enhanced glycogen resynthesis in exercised human skeletal muscle

“…Besides, increased ability of skeletal muscle to oxidise fat and sparing of muscle glycogen stores is an important phenomenon to improve the endurance performance. In this context, oral administration of hydroxycitrate has been shown to enhance the glycogen synthesis in exercised human skeletal muscle (Cheng et al, 2012). Glycogen synthesis is regulated by a number of physiological events, including training status, exercise routines and diet (Ivy, 1991).…”