Synephrine Boosts Metabolic Rate
By Jeff Volek - Chat with Doug on the
ProSource Fitness Forum
Aug 9, 2012
Nutrients that raise metabolic rate hold promise in the battle against the bulge. Although a wide array of nutrients show up in various thermogenic concoctions, few have been evaluated in research studies. A unique compound isolated from peels of immature fruits may be key to sparking a sluggish metabolism.
That compound is synephrine, a protoalkaloid in bitter orange extract which is derived from Citrus aurantium. Chemically, synephrine is very similar to the fight or flight hormone adrenaline (also known as epinephrine). Synephrine is both an Î±-adrenergic and Î²-adrenergic agonist simply meaning that it acts on those receptors in a positive way. Studies have shown synephrine specifically stimulates fat breakdown, an effect that is attributed primarily to stimulation of Î²3 adrenergic receptors, whereas stimulation of Î²1 and Î²2 adrenergic receptors are linked with cardiac effects. Thus synephrine is expected to be associated with less stimulation of heart rate and blood pressure while still promoting fat breakdown and thermogenesis.
In order to evaluate how much synephrine raises metabolic rate, researchers recently tested its effect alone and with other potentially synergistic compounds hesperidin and naringin present in Citrus aurantium. They had subjects consume different combinations of synephrine, hesperidin and naringin and monitored metabolic rate, heart rate, and blood pressure 75 min later. Ingestion of 50 mg of synephrine alone increased metabolic rate by 35 kcal. When the same amount of synephrine was combined with 600 mg of naringin, metabolic rate increased 99 kcal. The addition of 100 mg of hesperidin raised metabolic rate even further (+153 kcal). Importantly there were no changes in heart rate of blood pressure with any of the combinations of nutrients. These findings are consistent with stimulatory effects of synephrine on metabolism, but not the cardiovascular system. The additional benefit synephrine in the presence of both hesperidin and naringin have implications for combining these in weight loss/fat loss supplements.
Stohs SJ, Preuss HG, Keith SC, Keith PL, Miller H, Kaats GR. Effects of p-synephrine alone and in combination with selected bioflavonoids on resting metabolism, blood pressure, heart rate and self-reported mood changes. Int J Med Sci. 2011 Apr 28;8(4):295-301.
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