April 8, 2011
BOZEMAN, Mo.A weight-management supplement containing bitter orange, caffeine and green tea does not lead to increased cardiovascular stress, but it may boost fat burning in people who keep caffeine intake low, according to a study that tested Advantra Z from Nutratech Inc., West Caldwell, NJ (Int J Med Sci. 2011 Mar 2;8(3):192-7).
American researchers led by John G. Seifert, Ph.D., from Montana State University, evaluated a dietary supplement that contained Advantra Z (6 percent p-synephrine yielding 13 mg p-synephrine), 176 mg caffeine in the form of guarana extract, 55.5 mg green tea extract and small amounts of other ingredients in 14 overweight females and nine overweight males (age 24.7±7.4 years with a body mass index [BMI] of 26.6±3.8) in a randomized, placebo-controlled, crossover, double blind study.
On day one, subjects entered the laboratory following an overnight fast. Heart rate and blood pressure were recorded and expired air was analyzed for 10 minutes of the session. The non-protein respiratory exchange ratio (RER), calculated from oxygen uptake and carbon dioxide production, was used as an index of fat and carbohydrate oxidation (the burning of fat and calories). The lower the RER, the greater the fat/carbohydrate oxidation.
At each of three meals, subjects ingested one capsule that was either a non-caloric placebo or the dietary supplement. On the following day, the subjects returned and repeated the protocol. Researchers reported, over a 24-hour period, each subject consumed four capsules for a total of 52 mg p-synephrine and 704 mg caffeine as part of the study.
No effects of the dietary supplement on heart rate, systolic and diastolic blood pressure or mean arterial pressure were observed, even in those with hypertension. No between- or within-group differences were observed when data were analyzed for gender and caffeine usage.
However, they did find a small but significant decrease in RER ratio for the low-caffeine user group in response to the supplement, suggesting an increase in fat/carbohydrate oxidation.
The researchers noted confusion and controversy exist regarding the cardiovascular effects of dietary supplements containing caffeine and bitter orange (Citrus aurantium). The primary protoalkaloidal ingredient in bitter orange extract is p-synephrine, which has some structural similarities to ephedrine and norepinehrine, but exhibits markedly different pharmacokinetic and receptor binding properties.
Nutratech noted this study used a larger number of subjects than other frequently referenced studies involving Advantra Z/bitter orange. In addition, the company pointed out this study employed a protocol that closely represents the way people take dietary supplements for weight loss/management: ingesting the supplement or placebo with each meal. In the past, most studies administered only a single dose.
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