Synephrine fights fat
by Jeff S. Volek, Ph.D., R.D.
Weight loss supplements often contain a variety of compounds promoted as thermogenics, which simply means they raise your metabolic rate.
Synephrine is a nutrient isolated from peels of immature fruits. The most common source of synephrine is bitter orange extract derived from Citrus aurantium. Chemically, synephrine is very similar to adrenaline (or epinephrine). Synephrine stimulates both a-adrenergic and ß-adrenergic receptors in the body. Studies have shown synephrine specifically stimulates ß3-adrenergic receptors, which regulate fat breakdown, whereas stimulation of ß1-and ß2-adrenergic receptors is 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 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 minutes after ingestion.
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 or 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.