Literature Briefs-With Analysis by Cydney E. McQueen, PharmD
Testing for Thermogenic Herbs
Source: Martinet A, et al. Thermogenic effects of commercially available plant preparations aimed at treating human obesity. Phytomedicine 1999;6:231-238.
Objective: To examine acute effects of 12 herbs on energy expenditure (EE) and respiratory quotient (RQ), a measure of the proportion of fat oxidization (burning fat as opposed to carbohydrates or other energy sources).
Design and Setting: Testing was done in a university medical school physiology lab in Switzerland. Thermogenicity of six herbs showing potential in early studies (n = 6 for each) was compared to placebo (n = 6 for each) in a double-blind trial; six herbs (n = 4 or 5) were tested in an open-label trial. In order to avoid boredom and "fidgeting," recumbent subjects watched "non-thermogenic" (no sex or violence) movies. Baseline measurements were taken for 30 minutes, the dose was given, then measurements were taken for either four or five periods of 45 minutes each.
Subjects: Ninety-seven healthy, non-smoking, non-obese men and women, ages 18-36. Patients had not had caffeine in 12-16 hours and arrived fasting.
Treatment: For the controlled trial: maté (Ilex paraguariensis), guarana (Paullinia cupana), ma huang (Ephedra sinica), blue flag (Iris versicolor), hazel (Corylus avellana), and sea fennel (Crithum maritimum). For the open trial: Malabar tamarind (Garcinia cambogia), green tea (Camellia thea), artichoke (Cynara scolymus), bladderwrack (Fucus vesiculosis), pokeweed (Phytolacca decandra), and brown algae (Laminaria digitata).
Dose/Route/Duration: One dose, ap-proximately one hour after awakening. Some herbs were taken in liquid extract or tincture form and others were in dry extract or whole powder form in capsules.
Outcome Measures: Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, EE, and RQ. Two types of calorimeters were used.
Results: In the open-label trial, all parameters remained unchanged with the exception of increased HR with brown algae. In the controlled trial, EE was unchanged or significantly decreased (sea fennel) in all groups. RQ was unchanged for blue flag and sea fennel; significantly increased for guarana, ephedra, and hazel, indicating a smaller proportion of fat oxidization; and significantly decreased for maté, indicating a larger proportion of fat oxidization. Maté and ephedra increased HR, guarana increased SBP, sea fennel decreased SBP, and hazel decreased DBP.
Strengths/Limitations: The study used commonly accepted, objective measurements: EE and RQ. Investigators discussed possible limitations, such as bioavailability. They stated "statistical power ... was adequate," although there was no mention of the number of patients needed for a specified power. Low doses were discussed as a possible limitation; however, plants with dosing information were taken at or near commonly recommended doses. A primary limitation is that the non-obese study patients are not the patients who will be likely to use these herbs and so any differences in effects could not be observed.
Level of Evidence: Level II, major limitations
Comments: The data are far from conclusive. The fact that ephedra, known to increase metabolic rate by sympathetic stimulation, caused no change in EE lends credence to the idea that there may be long-term effects not visible in acute testing. Maté extract does seem to deserve additional study.
Clinical Impact: Despite many limitations, results might be used to guide patients away from products containing sea fennel, guarana, ephedra, and hazel that are, at least based on these results, least likely to aid weight loss and may produce more side effects.
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