According to findings published in the International Journal of Medical Sciences , consumption of 100 mg hesperidin, 50 mg p-synephrine (from bitter orange), and 600 mg naringin increased the resting metabolic rate by about 18 percent.
“If one assumes that the product was taken twice a day for one year, the theoretical increase in calorie consumption would amount to over 31 pounds,” wrote the researchers, led by Professor Harry Preuss from Georgetown University Medical Center.
“However, the actual extent of weight loss if the product was consumed under these conditions remains to be determined,” they added.
Products reportedly containing bitter orange (Citrus aurantium) or p-synephrine, its predominant alkaloid, are typically positioned in the weight loss segment, and reports also suggest efficacy in the relief of heartburn, and loss of appetite, as well as skin infections such as ringworm and athlete's foot.
The ingredient’s profile has increased since ephedra was banned by the US Food and Drug Administration (FDA) in 2004 as it contains similar compounds and has been favored by dietary supplements manufacturers as an ephedra substitute. It is most often consumed in pill-form but can also be applied to the skin.
The study used the patented bitter orange extract Advantra Z, which is commercialized by Nutratech Inc. The company also funded the study and one of the study authors is affiliated with the New Jersey based company.
Lead author Sidney Stohs from Creighton University and corresponding author Harry Preuss from Georgetown University have both served as consultants to Nutratech.
The bitter orange extract is standardized to 60 percent p-Synephrine.
The researchers tested the potential of p-synephrine alone, or p-synephrine plus naringin, or p-synephrine plus naringin and hesperidin, compared to placebo, on the metabolic rate of 50 volunteers.
Results showed that the p-synephrine alone increased the metabolic rate by 7 percent, compared to placebo. When 50mg of p-synephrine was consumed with 600 mg naringin and 100 mg hesperidin the metabolic rate was almost 18 percent higher than the control group.
“None of the treatment groups exhibited changes in heart rate or blood pressure relative to the control group, nor there were no differences in self-reported ratings of 10 symptoms between the treatment groups and the control group,” report Prof Preuss and his co-workers.
“This unusual finding of a thermogenic combination of ingredients that elevated metabolic rates without corresponding elevations in blood pressure and heart-rates warrants longer term studies to assess its value as a weight control agent,” they added.
Commenting on the potential mechanism, Prof Preuss and his co-workers note that the thermogenic effect of p-synephrine may be increased by naringin and hesperidin via an enhancement in the production of the expression of adiponectin, a hormone released from fat cells, which plays an important role in the regulation of insulin sensitivity and energy.
There have been some questions raised over the safety of bitter orange-containing supplements. Dr Stohs recently reviewed the 22 reports submitted to the Center for Food Safety and Applied Nutrition (CFSAN) of the US Food and Drug Administration (FDA) in the Journal of Functional Foods (doi: 10.1016/j.jff.2010.10.003).
Dr Stohs concluded that, given the “poly-herbal, poly-alkaloidal composition of the products involved” it was “unwarranted and unjustified” to say that bitter orange and p-synephrine were responsible for adverse events.
Source: International Journal of Medical Sciences
Volume 8, Issue 4, Pages 295-301
“Effects of p-Synephrine alone and in Combination with Selected Bioflavonoids on Resting Metabolism, Blood Pressure, Heart Rate and Self-Reported Mood Changes”
Authors: S.J. Stohs, H.G. Preuss, S.C. Keith, P.L Keith, H. Miller, G.R Kaats